Clin Drug Investig (2014) 34:173–182 DOI 10.1007/s40261-013-0161-2
ORIGINAL RESEARCH ARTICLE
Pharmacokinetic Drug Interactions of Afatinib with Rifampicin and Ritonavir Sven Wind • Thomas Giessmann • Arvid Jungnik Tobias Brand • Kristell Marzin • Julia Bertulis • Julia Hocke • Dietmar Gansser • Peter Stopfer
•
Published online: 8 January 2014 Ó Springer International Publishing Switzerland 2014
Abstract Background and Objective Afatinib is a potent, irreversible, ErbB family blocker in clinical development for the treatment of advanced non-small cell lung cancer, metastatic head and neck cancer, and other solid tumours. As afatinib is a substrate for the P-glycoprotein (P-gp) pump transporter the three studies presented here investigated the pharmacokinetics of afatinib in the presence of a potent inhibitor (ritonavir) or inducer [rifampicin (rifampin)] of P-gp. Methods We conducted phase I, open-label, single-centre studies in healthy male volunteers who received a single once-daily oral dose of afatinib (20 or 40 mg) together with either ritonavir or rifampicin; two studies had a randomised, two- and three-way crossover design and the third was a non-randomised, two-period sequential study.
Electronic supplementary material The online version of this article (doi:10.1007/s40261-013-0161-2) contains supplementary material, which is available to authorized users. S. Wind (&) T. Giessmann A. Jungnik T. Brand K. Marzin J. Bertulis P. Stopfer Translational Medicine and Clinical Pharmacology, Boehringer Ingelheim Pharma GmbH & Co KG, Birkendorfer Strasse 65, 88397 Biberach an der Riss, Germany e-mail: [email protected] J. Hocke Biostatistics Europe, Boehringer Ingelheim Pharma GmbH & Co KG, Biberach an der Riss, Germany D. Gansser Drug Metabolism and Pharmacokinetics, Boehringer Ingelheim Pharma GmbH & Co KG, Biberach an der Riss, Germany
Results When afatinib 20 mg was administered 1 h after ritonavir, afatinib geometric mean (gMean) maximum plasma concentration (Cmax) and area under the plasma concentration–time curve from time zero to infinity (AUC?) increased by 38.5 and 47.6 %, respectively. Coadministration of ritonavir either simultaneously or 6 h later than afatinib 40 mg resulted in minimal increase in the afatinib gMean Cmax and AUC? (4.1 and 18.6 % for simultaneous administration with AUC? not completely within the bioequivalence limits; 5.1 and 10.8 % for timed administration within the bioequivalence limits). Administration of afatinib 40 mg in the presence of rifampicin led to reduction in Cmax and AUC? by 21.6 and 33.8 %, respectively. In all studies, P-gp modulation mainly affected the extent of absorption of afatinib; there was no change in the terminal elimination half-life. The overall safety profile of afatinib was acceptable. Conclusion Coadministration of potent P-gp modulators had no clinically relevant effect on afatinib exposure. Effects of potent P-gp inhibitors were minimal at higher afatinib doses and can be readily managed by the timing of concomitant therapy. As afatinib is not a relevant modulator or substrate of cytochrome P450 enzymes, the drug– drug interaction potential is considered to be low.
1 Introduction Afatinib is a potent and selective, irreversible blocker of the ErbB family of transmembrane tyrosine kinase receptors, which includes epidermal growth factor receptor (EGFR, also known as ErbB1), ErbB2 (HER2), ErbB3 and ErbB4 [1, 2]. It has activity in a wide range of tumour cell lines that harbour a hyperactivated ErbB signalling network.
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Afatinib has been studied in patients with various solid tumours, including advanced non-small cell lung cancer (NSCLC) and metastatic head and neck cancer [3–5]. Afatinib is under regulatory review for treatment of patients with EGFR mutation-positive NSCLC and has already been approved for use in some countries [6]. Following administration in patients with solid tumours, afatinib is absorbed with maximum plasma concentration (Cmax) achieved at 2–5 h. Exposure [Cmax and area under the plasma concentration–time curve (AUC)] values increase slightly more than proportionally in the dose range of 20–50 mg of afatinib [7]. Afatinib exhibits bi-exponential elimination and an apparent terminal elimination half-life (t) around 37 h [7]. Afatinib undergoes minimal metabolism governed mainly by non-enzyme-catalysed Michael adduct formation to proteins and nucleophilic small molecules. Oxidative metabolism mediated via cytochrome P450 (CYP) is of negligible importance for the elimination of afatinib. Most of the dose is eliminated unchanged via the faeces, while contribution of renal excretion is low [8]. In recent years, there has been growing interest in the role of the P-glycoprotein (P-gp) pump and other transporters in the pharmacokinetics of drugs and how these transporters can modulate drug–drug interactions [9–11]. P-gp is a member of the adenosine triphosphate (ATP)binding (ABC) cassette transporters and is one of the best characterised human efflux transporters. However, understanding drug–drug interactions mediated by P-gp is often complicated by the overlap in substrate specificity between P-gp and CYP3A enzyme (CYP3A4) [9]. Afatinib was found to be a substrate of P-gp in vitro [estimated Michaelis–Menten constant (Km) 10–30 lmol/L in CaCo-2 cells and 9.3 lmol/L in human P-gp-expressing LLC-PK1 cells] [12], and thus modulators of P-gp may influence the absorption, distribution and elimination of afatinib in vivo. Therefore, drug–drug interaction studies were conducted in healthy subjects to assess the effects of coadministration with representative examples of a potent inhibitor (ritonavir) or potent inducer [rifampicin (rifampin)] of P-gp on afatinib exposure.
2 Subjects and Methods 2.1 Subjects Healthy male subjects aged 18–55 years with a body mass index between 18.5 and 29.9 kg/m2 were eligible for inclusion. All studies were conducted with approval of the relevant local ethics committee and written informed consent was obtained from all subjects before study entry. The main exclusion criteria included gastrointestinal,
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hepatic, renal, respiratory, cardiovascular, metabolic, skin, immunological or hormonal disorders; use of any drugs within 14 days prior to the first dose of study medication or during the trial (study 1 only); and use of drugs with a t of [24 h within 1 month prior to administration of trial medication or during the trial. 2.2 Study Design and Treatments Three phase I, single-centre, open-label studies were performed (Fig. 1), as outlined below. Study 1 had a randomised, 2-way crossover design. During the test treatment period, subjects received ritonavir 200 mg twice daily on 3 consecutive days and a single oral dose of afatinib 20 mg in the morning of the second day 1 h after ritonavir. During the reference treatment, subjects received a single dose of afatinib 20 mg on the second day. There was a washout of at least 21 days between the two doses of afatinib. Study 2 (NCT01426958) had a randomised, three-way crossover design. Subjects received one of the following treatments: a single dose of afatinib 40 mg was given either alone (Treatment A), together with (Treatment B) or 6 h before (Treatment C) ritonavir. In Treatments B and C, ritonavir 200 mg was given twice daily for 3 days (with pharmacokinetic profiling of afatinib on the second day). There was a washout period of at least 21 days between the three doses of afatinib. Study 3 (NCT01396265) had a two-period, fixedsequence design. In the first period, subjects received a single oral dose of afatinib 40 mg on the first day (reference treatment), and in the second period, oral rifampicin 600 mg was given in the evening for 7 days prior to a single oral dose of afatinib 40 mg the next morning (test treatment). There was a washout of at least 21 days between the afatinib doses. Afatinib was supplied as 20 or 40 mg film-coated tablets (Boehringer Ingelheim Pharma GmbH & Co KG, Biberach, Germany), ritonavir as 100 mg capsules (study 1) and 100 mg tablets (study 2) (NorvirÒ, Abbott Laboratories Limited, Maidenhead, UK), and rifampicin as 600 mg filmcoated tablets (EremfatÒ, RIEMSER Arzneimittel AG, Greifswald, Germany). In all studies, oral doses of afatinib were administered after an overnight fast (at least 10 h) at approximately 08:00 h (09:00 h in study 1) with 240 mL of tap water. Water was allowed ad libitum except 1 h before and after drug administration. Lunch was served not before 3 h following afatinib administration. 2.3 Pharmacokinetic Assessment and Analysis The primary endpoints in all three studies were the AUC from time zero to infinity (AUC?), the AUC from time
Pharmacokinetic Drug Interactions of Afatinib Study 1
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22 healthy male volunteers Randomisation
Group 1
Period 1: 3 days
Group 2
Ritonavir 200 mg twice-daily on days 1-3 + afatinib 20 mg on day 2
Afatinib 20 mg on day 2
21 day washout period
Period 2: 3 days
Afatinib 20 mg
Ritonavir 200 mg twice-daily on days 1-3 + afatinib 20 mg on day 2
24 healthy male volunteers
Study 2
Randomisation
Period 1: 3 days
Treatment A
Treatment B
Treatment C
Single dose of afatinib 40 mg
Ritonavir 200 mg twice-daily on days 1-3 + simultaneous afatinib 40 mg on day 2
Ritonavir 200 mg twice-daily on days 1-3 + afatinib 40 mg 6 h before dose on day 2
21 day washout period
Period 2: 3 days
Ritonavir 200 mg twice-daily on days 1-3 + afatinib 40 mg 6 h before dose on day 2
Single dose of afatinib 40 mg
Ritonavir 200 mg twice-daily on days 1-3 + simultaneous afatinib 40 mg on day 2
21 day washout period
Period 3: 3 days
Ritonavir 200 mg twice-daily on days 1-3 + simultaneous afatinib 40 mg on day 2
Ritonavir 200 mg twice-daily on days 1-3 + afatinib 40 mg 6 h before dose on day 2
Study 3 22 healthy male volunteers
Period 1: 1 day
Afatinib 40 mg on day 1
21 day washout period
Period 2: 8 days
Fig. 1 Study design
Rifampicin 600 mg daily nocte on days 1-7 and afatinib 40 mg mane on day 8
Single dose of afatinib 40 mg
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zero to the last quantifiable datapoint (AUClast) and Cmax. Secondary pharmacokinetic endpoints included the time to Cmax (tmax) and t. The ratio of urinary concentrations of 6-b-hydroxycortisol to cortisol, a marker of human hepatic induction of CYP3A4 by rifampicin, was another parameter of interest in study 3. In all three studies, venous blood samples for measurement of afatinib plasma concentrations were collected in potassium-EDTA-anticoagulant tubes pre-dose and at 0.5, 1, 2, 3, 4, 5, 6, 7, 12, 24, 48, 72, 96 and 120 h after administration of a single dose of afatinib. In study 1, samples were also collected at 9 and 35 h post-dose, and in studies 2 and 3 they were collected at 8, 10 and 36 h postdose. Samples were centrifuged within 30 to 40 min of collection and plasma stored at -20 °C until analysis. Plasma concentrations of afatinib were analysed using validated high-performance liquid chromatography–mass spectrometry (HPLC–MS/MS) methods at Boehringer Ingelheim Pharma GmbH & Co. KG, Biberach, Germany (study 1) and at Nuvisan GmbH & Co. KG, Neu-Ulm, Germany (studies 2 and 3). The calibration curves for afatinib covered ranges of 0.100–20.0 (study 1), 0.500–250 (study 2) and 0.100–50.0 (study 3) ng/mL plasma in undiluted samples. In study 3, the 6-b-hydroxycortisol/cortisol ratio was assessed in morning spot urine samples collected after the first morning voids, but before administration of afatinib in each treatment period. Urinary concentrations of cortisol and 6-b-hydroxycortisol were analysed by a validated HPLC–MS/MS method at SGS Cephac Europe, St. Benoıˆt, France. The calibration curves for cortisol and 6-b-hydroxycortisol ranged between 1–100 and 10–3,000 ng/mL, respectively. Induction of CYP3A4 by rifampicin was assessed by the change in the ratio of 6-b-hydroxycortisol/ cortisol after 7 days treatment with rifampicin relative to baseline (before rifampicin). 2.4 Statistical Analyses Non-compartmental analysis of plasma concentration–time data was performed using WinNonlinÒ Professional Network Version 5.2 software (Pharsight Corporation, Cary,
NC, USA). Standard non-compartmental methods were used to calculate pharmacokinetic parameters as described previously [7]. Statistical analyses were performed using SASÒ, version 8.2 and 9.2 (SAS Institute Inc., Cary, NC, USA). The log-transformed AUC?, AUClast and Cmax values for afatinib either alone or with coadministered treatments were analyzed using an ANOVA model with the following sources of variation: treatment, subject (or subject within sequence in studies 1 and 2), as well as period and sequence for studies 1 and 2. Afatinib alone was the reference treatment, while afatinib with coadministration was the test treatment. For the primary endpoints, 90 % confidence intervals (CIs) were computed, then backtransformed to the original scale to provide the point estimator and interval estimates for the geometric mean (gMean) of intra-subject test/reference ratio. For all other parameters, descriptive statistics were presented.
3 Results The baseline demographics of the 68 Caucasian subjects included in the three studies are shown in Table 1. 3.1 Effect of Ritonavir on the Pharmacokinetics of Afatinib 20 mg Twenty-two healthy male volunteers were enrolled and completed study 1. The afatinib plasma concentration–time profiles are shown in Fig. 2 and summarised pharmacokinetic parameters are given in Table 2. Absorption of afatinib 20 mg was moderately slow, with Cmax reached a median of 4 h after administration with and without ritonavir. Coadministration of ritonavir increased the gMean afatinib exposure by 47.6 % (90 % CI for gMean ratio 1.337–1.629) based on AUC?, and by 38.5 % (90 % CI for gMean ratio 1.206–1.589) based on Cmax. The plasma concentration–time curves of afatinib (with or without ritonavir) exhibited a parallel decline, indicating that the distribution and elimination phases of afatinib appeared to be unaffected by ritonavir cotreatment (Fig. 2). The gMean terminal t of afatinib was unchanged (34.1 h with ritonavir vs. 35.9 h without ritonavir). Intra-individual
Table 1 Baseline characteristics of the male study populations Characteristic
Study 1 (n = 22)
Study 2 (n = 24)
Study 3 (n = 22)
Age (years)
38.2 ± 8.8 (21–49)
38.0 ± 8.3 (18–51)
32.7 ± 8.3 (22–48)
Weight (kg)
82.5 ± 9.4
87.0 ± 10.3
80.8 ± 7.4
BMI (kg/m2)
25.6 ± 2.1
26.0 ± 2.2
25.2 ± 1.7
Data shown as mean ± standard deviation (range) BMI body mass index
Afatinib plasma concentration [ng/mL]
Pharmacokinetic Drug Interactions of Afatinib
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100
10
1
0.1 0
12
24
36
48
60
72
84
96
108
120
Time [hours] Afatinib 20 mg (n=22)
Afatinib 20 mg + ritonavir (n=22)
Fig. 2 Geometric mean plasma concentrations of afatinib versus time after single oral administration of afatinib 20 mg alone or with ritonavir 200 mg to healthy male volunteers (semi-logarithmic scale)
comparisons of the exposure parameter AUC? between treatments show an increase in the majority of subjects when afatinib was given in combination with ritonavir (see Fig. S1 in the Electronic Supplementary Material 1). 3.2 Effect of Simultaneous and Timed Administration of Ritonavir on the Pharmacokinetics of Afatinib 40 mg Of 24 subjects enrolled in study 2, two discontinued due to adverse events (see Safety section for further details). Available data from all 24 subjects were included in the pharmacokinetic analysis. Plasma concentration–time profiles of afatinib were similar when given alone or with ritonavir (Fig. S2 in the Electronic Supplementary Material 1). Table 3 shows a comparison of gMean pharmacokinetic parameters of afatinib for the three treatment periods.
With simultaneous administration of ritonavir, gMean afatinib AUC? increased by 18.6 % (90 % CI for gMean ratio 1.117–1.258), and Cmax was within the standard bioequivalence limits (0.8–1.25) with an increase of 4.1 % (90 % CI for gMean ratio 0.967–1.120). Intra-individual variability was low [geometric coefficient of variation (gCV) values between 11.5 and 14.2 %]. With ritonavir administered 6 h later, afatinib pharmacokinetic parameters were completely within the bioequivalence limits: gMean afatinib AUC? increased by 10.8 % (90 % CI for gMean ratio 1.049–1.169), and Cmax increased by 5.1 % (90 % CI for gMean ratio 0.964–1.145). Intra-individual variability was low (gCV values between 10.0 and 16.1 %). Intra-individual comparisons between AUC? for the three treatments are shown in Fig. 3, and demonstrate that for most subjects, afatinib exposure was somewhat higher for administration of concomitant ritonavir or timed ritonavir than for afatinib alone. The tmax and gMean terminal t of afatinib was not affected by ritonavir (Table 3). 3.3 Effect of Rifampicin on the Pharmacokinetics of Afatinib 40 mg Twenty-two healthy male volunteers were enrolled in and completed study 3. The afatinib plasma concentration–time profile is shown in Fig. 4 (see Fig. S3 in the Electronic Supplementary Material 1 for linear scale) and pharmacokinetic parameters are summarised in Table 4. In combination with rifampicin, afatinib AUC? decreased by 33.8 % (90 % CI for gMean ratio 0.608–0.721), and Cmax decreased by 21.6 % (90 % CI for gMean ratio 0.724–0.850). Inter-individual variability of exposure parameters was moderate and similar for the two treatments (gCV values ranging from 32.1 to 39.8 %), and intra-individual variability was low (gCV
Table 2 Pharmacokinetic parameters of afatinib after single oral administration of afatinib 20 mg alone (reference), and together with ritonavir 200 mg twice-daily for 3 days, when the third ritonavir dose was administered 1 h before afatinib (test) Parameter and unit
Afatinib 20 mga Alone (n = 22) (reference)
? Ritonavir (n = 22) (test)
Adjusted gMean ratios (90 % CI)
Intra-individual gCV (%)
19.2
AUC? (ngh/mL)
165 (37.9)
243 (26.0)
1.476 (1.337–1.629)
AUClast (ngh/mL)
153 (39.7)
228 (27.1)
1.490 (1.345–1.651)
19.9
Cmax (ng/mL)
7.71 (47.4)
10.7 (30.0)
1.385 (1.206–1.589)
27.0
tmaxb (h)
4.0 (0.5–5.0)
4.0 (3.98–5.0)
t (h)
35.9 (25.1)
34.1 (16.8)
AUC? area under the plasma concentration–time curve from time zero to infinity, AUClast area under the plasma concentration–time curve from time zero to the last quantifiable drug plasma concentration, Cmax maximum observed plasma concentration, CI confidence interval, gCV (%) geometric coefficient of variation (%), gMean geometric mean, tmax time to reach Cmax, t terminal elimination half-life a
Results are presented as gMean (gCV%) unless specified
b
These values are expressed as median (range)
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Table 3 Pharmacokinetic parameters of afatinib after single oral administration of afatinib 40 mg alone (reference) and together with ritonavir 200 mg twice daily for 3 days, when the third ritonavir dose was administered together with (simultaneous) or 6 h after afatinib (timed) Parameter and unit
Afatinib 40 mga Alone (n = 22)
? Simultaneous ritonavir (n = 24)
? Timed ritonavir (n = 22)
Simultaneous ritonavir/afatinib alone
Timed ritonavir/afatinib alone
Adjusted gMean ratio (90 % CI)
Adjusted gMean ratio (90 % CI)
Intraindividual gCV (%)
Intraindividual gCV (%)
AUC? (ngh/mL)
426 (22.8)
515 (27.5)
475 (19.4)
1.186 (1.117–1.258)
11.5
1.108 (1.049–1.169)
10.0
AUClast (ngh/mL)
392 (26.2)b
478 (27.9)
438 (20.3)
1.193 (1.122–1.268)
11.5
1.102 (1.038–1.170)
10.9
Cmax (ng/mL)
19.5 (33.5)
20.7 (29.4)
20.7 (24.4)
1.041 (0.967–1.120)
14.2
1.051 (0.964–1.145)
16.1
tmaxc
(h)
t (h)
6.0 (4.0–8.0)
6.0 (3.0–8.0)
6.0 (0.5–8.0)
33.0 (25.8)
32.5 (18.2)
33.9 (24.5)
AUC? area under the plasma concentration–time curve from time zero to infinity, AUClast area under the plasma concentration–time curve from time zero to the last quantifiable drug plasma concentration, Cmax maximum observed plasma concentration, CI confidence interval, gCV (%) geometric coefficient of variation (%), gMean geometric mean, tmax time to reach Cmax, t terminal elimination half-life Results are presented as gMean (gCV%) unless specified
b
n = 21
c
These values are expressed as median (range)
Afatinib plasma concentration [ng/mL]
a
Afatinib AUC∞ [ng•h/mL]
900 750 600 450 300 150
100
10
1
0.1 0
12
24
36
0
48
60
72
84
96
108
120
Time [hours] Afatinib 40 mg (n=22)
Afatinib 40 mg + simultaneous ritonavir (n=24)
Individual data
Afatinib 40 mg + timed ritonavir (n=22)
gMean
Fig. 3 Intra-individual comparison of afatinib AUC? after single oral administration of 40 mg afatinib alone, together with 200 mg ritonavir (simultaneous), or 6 h before 200 mg ritonavir (timed). AUC? area under the plasma concentration–time curve from time zero to infinity, gMean geometric mean
values between 15.6 and 16.5 %). Intra-individual comparisons of AUC? demonstrated that for almost all subjects, exposure decreased for the test treatment compared with the reference treatment (Fig. 5). The median tmax and the gMean terminal t of afatinib were comparable between the treatments. Compared with day 1, the urinary 6-b-hydroxycortisol/ cortisol ratio was increased by approximately 4.5-fold after 7 days’ treatment with rifampicin, from a gMean (gCV) 6-b-hydroxycortisol/cortisol ratio of 5.02 (66.2 %) to 22.5 (61.7 %).
Afatinib 40 mg (n=22)
Afatinib 40 mg + rifampicin (n=22)
Fig. 4 Geometric mean plasma concentrations of afatinib versus time after single oral administration of afatinib 40 mg alone (reference) or after single oral administration of afatinib 40 mg after 7 days’ treatment with rifampicin 600 mg/day (test) (semi-logarithmic scale)
3.4 Safety Across the three trials, 36.4–83.3 % of healthy male subjects reported one or more adverse events. The most common adverse events with afatinib were diarrhoea and headache. Most adverse events were of mild or moderate intensity (National Cancer Institute Common Terminology Criteria for Adverse Events Version 3.0 grade 1 or 2) and no serious adverse events were reported. A total of 14 (21.5 %) subjects had possible drug-related adverse events. Eight of these subjects experienced diarrhoea (seven in combination with ritonavir) and three subjects were noted to have an increase in lipase concentration [3 times the upper limit of normal (ULN). Asymptomatic increase in
Pharmacokinetic Drug Interactions of Afatinib
179
Table 4 Pharmacokinetic parameters of afatinib after single oral administration of afatinib 40 mg alone (reference) or after single oral administration of afatinib 40 mg after 7 days treatment with rifampicin (rifampin) 600 mg/day (test) Parameter and unit
Afatinib 40 mga
Adjusted gMean ratios (90 % CI)
Intra-individual gCV (%)
Alone (n = 22) (reference)
? Rifampicin (n = 21) (test)
Cmax (ng/mL)
38.3 (38.4)
30.0 (34.1)b
0.784 (0.724–0.850)
15.6
AUC? (ngh/mL)
912 (38.3)
610 (32.1)
0.662 (0.608–0.721)
16.1
AUClast (ngh/mL) tmaxc (h)
860 (39.8) 6.0 (5.0–7.0)
575 (32.3) 6.0 (3.0–8.0)b
0.662 (0.607––0.722)
16.5
t (h)
32.8 (18.4)
36.0 (15.1)
AUC? area under the plasma concentration–time curve from time zero to infinity, AUClast area under the plasma concentration–time curve from time zero to the last quantifiable drug plasma concentration, Cmax maximum observed plasma concentration, CI confidence interval, gCV (%) geometric coefficient of variation (%), tmax time to reach Cmax, t terminal elimination half-life a Results are presented as gMean (gCV%) unless specified b
n = 22
c
These values are expressed as median (range)
confirmed no pathological findings. In addition, one subject in study 3 with an abnormal baseline lipase concentration developed a transient increase in lipase 3 9 ULN after a single dose of afatinib (40 mg), which returned to normal within 24 h. A further dose of afatinib in combination with rifampicin was given in the second treatment period without any increase in lipase concentration.
2250
Afatinib AUC∞ [ng•h/mL]
2000 1750 1500 1250 1000 750
4 Discussion
500 250 0 Afatinib 40 mg (n=22)
Individual data
Afatinib 40 mg + rifampicin (n=21)
gMean
Fig. 5 Intra-individual comparisons of afatinib AUC? for test (afatinib 40 mg after 7 days’ treatment with rifampicin 600 mg/ day) and reference (afatinib 40 mg alone) treatments. AUC? area under the plasma concentration–time curve from time zero to infinity, gMean geometric mean
gamma-glutamyltransferase [2 9 ULN and rash were experienced by a further one subject each, and one subject reported dizziness, headache, nausea and vomiting. Two subjects in study 2 were withdrawn from treatment because of asymptomatic lipase elevation (grade 4); one of these subjects received cumulative doses of afatinib 80 mg and ritonavir 1,400 mg and the other received afatinib 40 mg and ritonavir 1,200 mg. One subject had a lipase concentration 8 9 ULN, which returned to normal at follow-up. The other subject had a lipase concentration up to 11 9 ULN. Lipase levels remained elevated after discontinuation of study treatment and were accompanied by a mild increase in amylase (\3 9 ULN), although C-reactive protein was normal. An ultrasound of the pancreas
Preclinical investigations have demonstrated that afatinib is a substrate for the efflux transporter protein P-gp. Therefore, these three studies aimed to investigate the pharmacokinetic drug–drug interactions of afatinib during coadministration with a potent P-gp inhibitor (ritonavir) and potent inducer (rifampicin). The first study investigated the effect of P-gp inhibition on afatinib exposure. A dose of afatinib 20 mg was used as higher doses had not been tested in healthy volunteers at this timepoint in clinical development and the effect of P-gp inhibition on afatinib exposure was unknown. Ritonavir was used as P-gp inhibitor, as it has been identified as a highly potent inhibitor of both P-gp and CYP3A4 [13– 15], and is considered an appropriate P-gp inhibitor to estimate the maximum increase in exposure of a drug [16, 17]. In view of the short t for ritonavir (3–5 h) [18], twice-daily administration (200 mg) would likely result in steady-state levels 1 day after administration. In line with this, afatinib was administered on day 2 of the 3-day ritonavir treatment period, which was chosen to avoid any inductive effects described for this compound and thereby diminish the inhibitory effect on P-gp [19]. The rate and extent of absorption of afatinib were increased by coadministration with ritonavir by 47.6 % for
180 Fig. 6 Effect of ritonavir and rifampicin (rifampin) on afatinib exposure. AUC area under the plasma concentration– time curve, CI confidence interval, Cmax maximum plasma concentration
S. Wind et al. Reference
Test
Afatinib 20 mg
with ritonavir [-1 h]
Afatinib 40 mg
with ritonavir [0 h]
Afatinib 40 mg
with ritonavir [+6 h]
Afatinib 40 mg
with rifampicin 0.80
1.00
1.25
Test/reference ratio ± 90% CI AUC test/reference ratio ± 90% CI Cmax test/reference ratio ± 90% CI
AUC? and 38.5 % for Cmax, which can be classified as mild according to current guidelines [17]. However, ritonavir did not influence the time to Cmax or the distribution and elimination phases of afatinib. Previous studies have shown that CYP3A4 enzyme-catalysed metabolic reactions play a subordinate role in the metabolism of afatinib in vivo and CYP3A4-dependent N-demethylation is too low to be quantitatively detected in healthy volunteers [8]. Therefore, the increase in afatinib exposure in the presence of ritonavir can most likely be attributed to increased bioavailability resulting from inhibition of intestinal P-gp-mediated transport processes during the absorption phase of afatinib. The second study investigated the effect of P-gp inhibition with ritonavir (200 mg twice daily for 3 days) when administered simultaneously or 6 h after afatinib. This design was chosen to be clinically more meaningful (simultaneous administration with a P-gp inhibitor) and to define a dosing schedule for a safe combination of the clinically more relevant 40 mg dose of afatinib with a potent P-gp inhibitor. As both ritonavir treatments (either simultaneous or timed administration) had little influence on afatinib exposure (adjusted gMean ratios of AUC parameters and Cmax for afatinib were bioequivalent and well within 0.80–1.25; only the upper 90 % CI of AUC parameters for the simultaneous ritonavir administration was slightly above 1.25) (Fig. 6), it can be concluded that there was no clinically relevant drug–drug interaction with ritonavir. The negligible effects on afatinib exposure in this trial compared with study 1 are likely due to differences in the trial design. First, the effect of P-gp transport on afatinib bioavailability is likely to be lower for the 40 mg than the 20 mg dose, consistent with a known slight over-proportional increase in exposure over the afatinib dose range of 20–50 mg [7]. This non-linear behaviour could potentially be caused by saturation of the P-gp transporter, which would explain increased effects
of ritonavir at lower doses of afatinib. Second, the staggered dosing of ritonavir applied in study 2 may have contributed to the negligible effect; afatinib absorption is assumed to be mainly complete when ritonavir was administered 6 h later. In contrast, the first study had a ‘‘maximum inhibition scenario’’, in which ritonavir was administered 1 h before afatinib to ensure there was optimal inhibition of intestinal P-gp transport at the time of afatinib administration. This maximal P-gp inhibition might have been already impacted by simultaneous administration of afatinib with ritonavir. The change of two parameters, dose and administration schedule, in parallel between studies 1 and 2 may limit a definitive assessment about why the treatment effect in study 2 was lower than in study 1. The effect observed could have been due to the higher dose or the different timing of ritonavir administration, or a mixture of both. The third study investigated the effect of potent induction of P-gp expression by pre-treatment for 7 days with rifampicin, which induces a number of drug-metabolising enzymes, including intestinal and hepatic P-gp and CYP3A in the liver and in the small intestine [14, 15]. Full induction of P-gp is reached about 1 week after starting rifampicin treatment (600 mg daily) and the induction dissipates in roughly 2 weeks after discontinuing rifampicin [20]. Measurement of a surrogate endpoint, the urinary 6-b-hydroxycortisol/cortisol ratio, confirmed this effect [21, 22]. Pre-treatment with rifampicin moderately decreased the exposure to afatinib by 33.8 % (based on AUC) and by 21.6 % (based on Cmax). This effect is presumably related to elevated P-gp expression levels leading to an increased efflux transport of afatinib. As coadministration of rifampicin did not influence tmax or terminal t of afatinib, the effects may be mainly explained by a decreased fraction of afatinib reaching systemic circulation due to increased intestinal efflux transport.
Pharmacokinetic Drug Interactions of Afatinib
Taken together, observations from these three studies suggest that P-gp modulation mainly affects the extent of absorption of afatinib. Considering the effect size of P-gp induction or inhibition in relation to the variability in afatinib exposure, it can be inferred that coadministration with any P-gp inducer or inhibitor (potent, moderate or mild) would not require any adjustment to the starting dose of afatinib. Although other strong P-gp inhibitors (including but not limited to cyclosporine, erythromycin, ketoconazole, itraconazole, quinidine, valspodar, verapamil, tacrolimus, nelfinavir, saquinavir and amiodarone) have not been studied, pharmacologically, any interactions are likely to be similar to that for ritonavir [6]. In order to further reduce the risk of any interaction, it is recommended to administer strong P-gp inhibitors, using staggered dosing. A similar effect with the use of staggered dosing was observed for the oral anticoagulant dabigatran etexilate (a P-gp substrate) when coadministered with verapamil [23]. Besides P-gp interactions, other transporters that may have clinically important effects on the drug absorption and disposition of afatinib have been studied [24]. In vitro, afatinib is a substrate as well as an inhibitor of the breast cancer resistance protein (BCRP) ([12]). As ritonavir was shown to be an inhibitor of BCRP in vitro [25] and its exposure should have been sufficiently high to inhibit BCRP in studies 1 and 2 [26], it is assumed that any effects on afatinib exposure based on BCRP inhibition were covered in both studies. Therefore, afatinib exposure should be at maximum mildly, if at all, increased by BCRP inhibition. Single doses of afatinib were well-tolerated when given alone and in combination with multiple doses of rifampicin or ritonavir to healthy male volunteers. The adverse events were in line with the known safety profile of afatinib. In two subjects, combined administration of ritonavir and afatinib was associated with asymptomatic lipase increases of 8 and 11 9 ULN. The study design did not allow definitive assessment of whether the effects were related to ritonavir and/or afatinib, and the observed increases were therefore considered as possibly related to both medications. Pancreatitis is considered a common adverse effect of ritonavir [18] and in afatinib-treated patients lipase elevation/pancreatitis has been reported infrequently. We acknowledge a number of limitations in these studies. First, the subjects included in each of the studies were all healthy male Caucasian subjects. Sex and ethnic differences in the therapeutic response to drug treatment are well-recognised but difficult to predict due to the large number of genetic and environmental factors that may influence drug disposition [27]. However, exploratory analyses looking at genetic P-gp polymorphisms do not suggest any correlation, and any significant afatinib
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exposure differences for race are not expected. Second, only single doses of afatinib were administered to all subjects. However, considering the over-proportional pharmacokinetics of afatinib in the therapeutic dose range of 20–50 mg, which are likely due to saturation of P-gp transport [7], it is expected that effects are more pronounced at lower, single doses. Thus, the effects of P-gp inhibition on afatinib exposure in patients after multiple dosing would be expected to be lower than in study 1 and be more in the range of study 2. In addition, multiple-dose administration of afatinib to healthy volunteers was not considered feasible due to the safety of the subjects. As the maximum effect of P-gp modulators was expected after single dosing of afatinib, the effects on afatinib exposure are over- rather than underestimated in the present studies, providing the most conservative approach for evaluation.
5 Conclusion Maximum inhibition or induction of P-gp as tested by coadministration of ritonavir and rifampicin had no clinically relevant effect on exposure to afatinib. Ritonavir administration simultaneously or 6 h after afatinib 40 mg had no relevant impact on afatinib exposure, indicating that P-gp inhibitors can be safely combined with afatinib while considering the timing of coadministration. The results of this study provide valuable information for the safe and effective use of afatinib in combination with potent P-gp inhibitors and inducers. As afatinib has no CYP liability and efflux transporter liability is mild and can be handled by timing of concomitant therapy, the drug–drug interaction potential of afatinib is considered to be low. Acknowledgments These studies were sponsored by Boehringer Ingelheim Pharma GmbH & Co. KG, Germany. The studies were conducted at the Human Pharmacology Centre, Boehringer Ingelheim Pharma GmbH & Co. KG, Biberach, Germany (principal investigator, Mario Iovino). Boehringer Ingelheim was responsible for the design and conduct of all of the studies, and the collection and management of the data. The authors were responsible for the analysis and interpretation of the data and the preparation of the manuscript. All authors are employees of Boehringer Ingelheim and were fully responsible for all content and editorial decisions, and were involved at all stages of the manuscript development.
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182 3. Sequist LV, Yang JC, Yamamoto N, et al. Phase III study of afatinib or cisplatin plus pemetrexed in patients with metastatic lung adenocarcinoma with EGFR mutations. J Clin Oncol. 2013;31:3327–34. 4. Wu YL, Zhou C, Hu CP, et al. LUX-Lung 6: a randomized, openlabel, phase III study of afatinib (A) versus gemcitabine/cisplatin (GC) as first-line treatment for Asian patients (pts) with EGFR mutation-positive (EGFR M?) advanced adenocarcinoma of the lung. J Clin Oncol 2013;31(Suppl):abstract 8016. 5. Cohen EEW, Fayette J, Cupissol D, et al. A randomized, openlabel, phase II study of afatinib (BIBW 2992) versus cetuximab in recurrent or metastatic squamous cell carcinoma of the head and neck: final data [abstract no. PP101]. Eur Arch Otorhinolaryngol. 2012;269:1374. 6. GilotrifTM (afatinib) tablet for oral use: US prescribing information. Ridgefield: Boehringer Ingelheim Pharmaceuticals, Inc.; 2013 Oct. http://www.gilotrif.com/. Accessed 21 Nov 2013. 7. Wind S, Schmid M, Erhardt J, et al. Pharmacokinetics of afatinib, a selective irreversible ErbB family blocker, in patients with advanced solid tumours. Clin Pharmacokinet. 2013;52:1101–9. 8. Stopfer P, Marzin K, Narjes H, et al. Afatinib pharmacokinetics and metabolism after oral administration to healthy male volunteers. Cancer Chemother Pharmacol. 2012;69:1051–61. 9. Lin JH, Yamazaki M. Role of P-glycoprotein in pharmacokinetics: clinical implications. Clin Pharmacokinet. 2003;42:59–98. 10. Mizuno N, Niwa T, Yotsumoto Y, et al. Impact of drug transporter studies on drug discovery and development. Pharmacol Rev. 2003;55:425–61. 11. Marzolini C, Paus E, Buclin T, et al. Polymorphisms in human MDR1 (P-glycoprotein): recent advances and clinical relevance. Clin Pharmacol Ther. 2004;75:13–33. 12. European Medicines Agency. Committee for Medicinal Products for Human Use (CHMP) assessment report for Giotrif (afatinib). 16 October 2013. http://www.ema.europa.eu/docs/en_GB/ document_library/EPAR_-_Public_assessment_report/human/ 002280/WC500152394.pdf. Accessed 20 Nov 2013. 13. Zhang L, Strong JM, Qiu W, et al. Scientific perspectives on drug transporters and their role in drug interactions. Mol Pharm. 2006;3:62–9. 14. Backman JT, Olkkola KT, Ojala M, et al. Concentrations and effects of oral midazolam are greatly reduced in patients treated with carbamazepine or phenytoin. Epilepsia. 1996;37:253–7. 15. Backman JT, Kivisto KT, Olkkola KT, et al. The area under the plasma concentration-time curve for oral midazolam is 400-fold larger during treatment with itraconazole than with rifampicin. Eur J Clin Pharmacol. 1998;54:53–8.
S. Wind et al. 16. FDA Center for Drug Evaluation and Research (CDER). Guidance for industry. Drug interaction studies—study design, data analysis, implications for dosing, and labeling recommendations. US FDA draft guidance, Feb 2012. http://www.fda.gov/ downloads/Drugs/GuidanceComplianceRegulatoryInformation/ Guidances/ucm292362.pdf Accessed 27 Aug 2013. 17. European Medicines Agency. Committee for Human Medicinal Products (CHMP). Guideline on the investigation of drug interactions, 21 June 2012. http://www.ema.europa.eu/docs/en_GB/ document_library/Scientific_guideline/2012/07/WC500129606. pdf. Accessed 27 Aug 2013. 18. NorvirÒ (ritonavir) tablet for oral use: US prescribing information. North Chicago: AbbVie Inc.; 2013 Nov. http://www.norvir. com/. Accessed 21 Nov 2013. 19. Hsu A, Granneman GR, Bertz RJ. Ritonavir. Clinical pharmacokinetics and interactions with other anti-HIV agents. Clin Pharmacokinet. 1998;35:275–91. 20. Niemi M, Backman JT, Fromm MF, et al. Pharmacokinetic interactions with rifampicin: clinical relevance. Clin Pharmacokinet. 2003;42:819–50. 21. Galteau MM, Shamsa F. Urinary 6beta-hydroxycortisol: a validated test for evaluating drug induction or drug inhibition mediated through CYP3A in humans and in animals. Eur J Clin Pharmacol. 2003;59:713–33. 22. Tran JQ, Kovacs SJ, McIntosh TS, et al. Morning spot and 24-hour urinary 6 beta-hydroxycortisol to cortisol ratios: intraindividual variability and correlation under basal conditions and conditions of CYP 3A4 induction. J Clin Pharmacol. 1999;39:487–94. 23. Ha¨rtter S, Sennewald R, Nehmiz G, et al. Oral bioavailability of dabigatran etexilate (PradaxaÒ) after co-medication with verapamil in healthy subjects. Br J Clin Pharmacol. 2013;75:1053–62. 24. International Transporter Consortium, Giacomini KM, Huang SM, et al. Membrane transporters in drug development. Nat Rev Drug Discov 2010;9:215–36. 25. Gupta A, Zhang Y, Unadkat JD, et al. HIV protease inhibitors are inhibitors but not substrates of the human breast cancer resistance protein (BCRP/ABCG2). J Pharmacol Exp Ther. 2004;310: 334–41. 26. Tachibana T, Kato M, Watanabe T, et al. Method for predicting the risk of drug–drug interactions involving inhibition of intestinal CYP3A4 and P-glycoprotein. Xenobiotica. 2009;39:430–43. 27. Yasuda SU, Zhang L, Huang SM. The role of ethnicity in variability in response to drugs: focus on clinical pharmacology studies. Clin Pharmacol Ther. 2008;84:417–23.
ORIGINAL RESEARCH ARTICLE
Pharmacokinetic Drug Interactions of Afatinib with Rifampicin and Ritonavir Sven Wind • Thomas Giessmann • Arvid Jungnik Tobias Brand • Kristell Marzin • Julia Bertulis • Julia Hocke • Dietmar Gansser • Peter Stopfer
•
Published online: 8 January 2014 Ó Springer International Publishing Switzerland 2014
Abstract Background and Objective Afatinib is a potent, irreversible, ErbB family blocker in clinical development for the treatment of advanced non-small cell lung cancer, metastatic head and neck cancer, and other solid tumours. As afatinib is a substrate for the P-glycoprotein (P-gp) pump transporter the three studies presented here investigated the pharmacokinetics of afatinib in the presence of a potent inhibitor (ritonavir) or inducer [rifampicin (rifampin)] of P-gp. Methods We conducted phase I, open-label, single-centre studies in healthy male volunteers who received a single once-daily oral dose of afatinib (20 or 40 mg) together with either ritonavir or rifampicin; two studies had a randomised, two- and three-way crossover design and the third was a non-randomised, two-period sequential study.
Electronic supplementary material The online version of this article (doi:10.1007/s40261-013-0161-2) contains supplementary material, which is available to authorized users. S. Wind (&) T. Giessmann A. Jungnik T. Brand K. Marzin J. Bertulis P. Stopfer Translational Medicine and Clinical Pharmacology, Boehringer Ingelheim Pharma GmbH & Co KG, Birkendorfer Strasse 65, 88397 Biberach an der Riss, Germany e-mail: [email protected] J. Hocke Biostatistics Europe, Boehringer Ingelheim Pharma GmbH & Co KG, Biberach an der Riss, Germany D. Gansser Drug Metabolism and Pharmacokinetics, Boehringer Ingelheim Pharma GmbH & Co KG, Biberach an der Riss, Germany
Results When afatinib 20 mg was administered 1 h after ritonavir, afatinib geometric mean (gMean) maximum plasma concentration (Cmax) and area under the plasma concentration–time curve from time zero to infinity (AUC?) increased by 38.5 and 47.6 %, respectively. Coadministration of ritonavir either simultaneously or 6 h later than afatinib 40 mg resulted in minimal increase in the afatinib gMean Cmax and AUC? (4.1 and 18.6 % for simultaneous administration with AUC? not completely within the bioequivalence limits; 5.1 and 10.8 % for timed administration within the bioequivalence limits). Administration of afatinib 40 mg in the presence of rifampicin led to reduction in Cmax and AUC? by 21.6 and 33.8 %, respectively. In all studies, P-gp modulation mainly affected the extent of absorption of afatinib; there was no change in the terminal elimination half-life. The overall safety profile of afatinib was acceptable. Conclusion Coadministration of potent P-gp modulators had no clinically relevant effect on afatinib exposure. Effects of potent P-gp inhibitors were minimal at higher afatinib doses and can be readily managed by the timing of concomitant therapy. As afatinib is not a relevant modulator or substrate of cytochrome P450 enzymes, the drug– drug interaction potential is considered to be low.
1 Introduction Afatinib is a potent and selective, irreversible blocker of the ErbB family of transmembrane tyrosine kinase receptors, which includes epidermal growth factor receptor (EGFR, also known as ErbB1), ErbB2 (HER2), ErbB3 and ErbB4 [1, 2]. It has activity in a wide range of tumour cell lines that harbour a hyperactivated ErbB signalling network.
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Afatinib has been studied in patients with various solid tumours, including advanced non-small cell lung cancer (NSCLC) and metastatic head and neck cancer [3–5]. Afatinib is under regulatory review for treatment of patients with EGFR mutation-positive NSCLC and has already been approved for use in some countries [6]. Following administration in patients with solid tumours, afatinib is absorbed with maximum plasma concentration (Cmax) achieved at 2–5 h. Exposure [Cmax and area under the plasma concentration–time curve (AUC)] values increase slightly more than proportionally in the dose range of 20–50 mg of afatinib [7]. Afatinib exhibits bi-exponential elimination and an apparent terminal elimination half-life (t) around 37 h [7]. Afatinib undergoes minimal metabolism governed mainly by non-enzyme-catalysed Michael adduct formation to proteins and nucleophilic small molecules. Oxidative metabolism mediated via cytochrome P450 (CYP) is of negligible importance for the elimination of afatinib. Most of the dose is eliminated unchanged via the faeces, while contribution of renal excretion is low [8]. In recent years, there has been growing interest in the role of the P-glycoprotein (P-gp) pump and other transporters in the pharmacokinetics of drugs and how these transporters can modulate drug–drug interactions [9–11]. P-gp is a member of the adenosine triphosphate (ATP)binding (ABC) cassette transporters and is one of the best characterised human efflux transporters. However, understanding drug–drug interactions mediated by P-gp is often complicated by the overlap in substrate specificity between P-gp and CYP3A enzyme (CYP3A4) [9]. Afatinib was found to be a substrate of P-gp in vitro [estimated Michaelis–Menten constant (Km) 10–30 lmol/L in CaCo-2 cells and 9.3 lmol/L in human P-gp-expressing LLC-PK1 cells] [12], and thus modulators of P-gp may influence the absorption, distribution and elimination of afatinib in vivo. Therefore, drug–drug interaction studies were conducted in healthy subjects to assess the effects of coadministration with representative examples of a potent inhibitor (ritonavir) or potent inducer [rifampicin (rifampin)] of P-gp on afatinib exposure.
2 Subjects and Methods 2.1 Subjects Healthy male subjects aged 18–55 years with a body mass index between 18.5 and 29.9 kg/m2 were eligible for inclusion. All studies were conducted with approval of the relevant local ethics committee and written informed consent was obtained from all subjects before study entry. The main exclusion criteria included gastrointestinal,
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hepatic, renal, respiratory, cardiovascular, metabolic, skin, immunological or hormonal disorders; use of any drugs within 14 days prior to the first dose of study medication or during the trial (study 1 only); and use of drugs with a t of [24 h within 1 month prior to administration of trial medication or during the trial. 2.2 Study Design and Treatments Three phase I, single-centre, open-label studies were performed (Fig. 1), as outlined below. Study 1 had a randomised, 2-way crossover design. During the test treatment period, subjects received ritonavir 200 mg twice daily on 3 consecutive days and a single oral dose of afatinib 20 mg in the morning of the second day 1 h after ritonavir. During the reference treatment, subjects received a single dose of afatinib 20 mg on the second day. There was a washout of at least 21 days between the two doses of afatinib. Study 2 (NCT01426958) had a randomised, three-way crossover design. Subjects received one of the following treatments: a single dose of afatinib 40 mg was given either alone (Treatment A), together with (Treatment B) or 6 h before (Treatment C) ritonavir. In Treatments B and C, ritonavir 200 mg was given twice daily for 3 days (with pharmacokinetic profiling of afatinib on the second day). There was a washout period of at least 21 days between the three doses of afatinib. Study 3 (NCT01396265) had a two-period, fixedsequence design. In the first period, subjects received a single oral dose of afatinib 40 mg on the first day (reference treatment), and in the second period, oral rifampicin 600 mg was given in the evening for 7 days prior to a single oral dose of afatinib 40 mg the next morning (test treatment). There was a washout of at least 21 days between the afatinib doses. Afatinib was supplied as 20 or 40 mg film-coated tablets (Boehringer Ingelheim Pharma GmbH & Co KG, Biberach, Germany), ritonavir as 100 mg capsules (study 1) and 100 mg tablets (study 2) (NorvirÒ, Abbott Laboratories Limited, Maidenhead, UK), and rifampicin as 600 mg filmcoated tablets (EremfatÒ, RIEMSER Arzneimittel AG, Greifswald, Germany). In all studies, oral doses of afatinib were administered after an overnight fast (at least 10 h) at approximately 08:00 h (09:00 h in study 1) with 240 mL of tap water. Water was allowed ad libitum except 1 h before and after drug administration. Lunch was served not before 3 h following afatinib administration. 2.3 Pharmacokinetic Assessment and Analysis The primary endpoints in all three studies were the AUC from time zero to infinity (AUC?), the AUC from time
Pharmacokinetic Drug Interactions of Afatinib Study 1
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22 healthy male volunteers Randomisation
Group 1
Period 1: 3 days
Group 2
Ritonavir 200 mg twice-daily on days 1-3 + afatinib 20 mg on day 2
Afatinib 20 mg on day 2
21 day washout period
Period 2: 3 days
Afatinib 20 mg
Ritonavir 200 mg twice-daily on days 1-3 + afatinib 20 mg on day 2
24 healthy male volunteers
Study 2
Randomisation
Period 1: 3 days
Treatment A
Treatment B
Treatment C
Single dose of afatinib 40 mg
Ritonavir 200 mg twice-daily on days 1-3 + simultaneous afatinib 40 mg on day 2
Ritonavir 200 mg twice-daily on days 1-3 + afatinib 40 mg 6 h before dose on day 2
21 day washout period
Period 2: 3 days
Ritonavir 200 mg twice-daily on days 1-3 + afatinib 40 mg 6 h before dose on day 2
Single dose of afatinib 40 mg
Ritonavir 200 mg twice-daily on days 1-3 + simultaneous afatinib 40 mg on day 2
21 day washout period
Period 3: 3 days
Ritonavir 200 mg twice-daily on days 1-3 + simultaneous afatinib 40 mg on day 2
Ritonavir 200 mg twice-daily on days 1-3 + afatinib 40 mg 6 h before dose on day 2
Study 3 22 healthy male volunteers
Period 1: 1 day
Afatinib 40 mg on day 1
21 day washout period
Period 2: 8 days
Fig. 1 Study design
Rifampicin 600 mg daily nocte on days 1-7 and afatinib 40 mg mane on day 8
Single dose of afatinib 40 mg
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zero to the last quantifiable datapoint (AUClast) and Cmax. Secondary pharmacokinetic endpoints included the time to Cmax (tmax) and t. The ratio of urinary concentrations of 6-b-hydroxycortisol to cortisol, a marker of human hepatic induction of CYP3A4 by rifampicin, was another parameter of interest in study 3. In all three studies, venous blood samples for measurement of afatinib plasma concentrations were collected in potassium-EDTA-anticoagulant tubes pre-dose and at 0.5, 1, 2, 3, 4, 5, 6, 7, 12, 24, 48, 72, 96 and 120 h after administration of a single dose of afatinib. In study 1, samples were also collected at 9 and 35 h post-dose, and in studies 2 and 3 they were collected at 8, 10 and 36 h postdose. Samples were centrifuged within 30 to 40 min of collection and plasma stored at -20 °C until analysis. Plasma concentrations of afatinib were analysed using validated high-performance liquid chromatography–mass spectrometry (HPLC–MS/MS) methods at Boehringer Ingelheim Pharma GmbH & Co. KG, Biberach, Germany (study 1) and at Nuvisan GmbH & Co. KG, Neu-Ulm, Germany (studies 2 and 3). The calibration curves for afatinib covered ranges of 0.100–20.0 (study 1), 0.500–250 (study 2) and 0.100–50.0 (study 3) ng/mL plasma in undiluted samples. In study 3, the 6-b-hydroxycortisol/cortisol ratio was assessed in morning spot urine samples collected after the first morning voids, but before administration of afatinib in each treatment period. Urinary concentrations of cortisol and 6-b-hydroxycortisol were analysed by a validated HPLC–MS/MS method at SGS Cephac Europe, St. Benoıˆt, France. The calibration curves for cortisol and 6-b-hydroxycortisol ranged between 1–100 and 10–3,000 ng/mL, respectively. Induction of CYP3A4 by rifampicin was assessed by the change in the ratio of 6-b-hydroxycortisol/ cortisol after 7 days treatment with rifampicin relative to baseline (before rifampicin). 2.4 Statistical Analyses Non-compartmental analysis of plasma concentration–time data was performed using WinNonlinÒ Professional Network Version 5.2 software (Pharsight Corporation, Cary,
NC, USA). Standard non-compartmental methods were used to calculate pharmacokinetic parameters as described previously [7]. Statistical analyses were performed using SASÒ, version 8.2 and 9.2 (SAS Institute Inc., Cary, NC, USA). The log-transformed AUC?, AUClast and Cmax values for afatinib either alone or with coadministered treatments were analyzed using an ANOVA model with the following sources of variation: treatment, subject (or subject within sequence in studies 1 and 2), as well as period and sequence for studies 1 and 2. Afatinib alone was the reference treatment, while afatinib with coadministration was the test treatment. For the primary endpoints, 90 % confidence intervals (CIs) were computed, then backtransformed to the original scale to provide the point estimator and interval estimates for the geometric mean (gMean) of intra-subject test/reference ratio. For all other parameters, descriptive statistics were presented.
3 Results The baseline demographics of the 68 Caucasian subjects included in the three studies are shown in Table 1. 3.1 Effect of Ritonavir on the Pharmacokinetics of Afatinib 20 mg Twenty-two healthy male volunteers were enrolled and completed study 1. The afatinib plasma concentration–time profiles are shown in Fig. 2 and summarised pharmacokinetic parameters are given in Table 2. Absorption of afatinib 20 mg was moderately slow, with Cmax reached a median of 4 h after administration with and without ritonavir. Coadministration of ritonavir increased the gMean afatinib exposure by 47.6 % (90 % CI for gMean ratio 1.337–1.629) based on AUC?, and by 38.5 % (90 % CI for gMean ratio 1.206–1.589) based on Cmax. The plasma concentration–time curves of afatinib (with or without ritonavir) exhibited a parallel decline, indicating that the distribution and elimination phases of afatinib appeared to be unaffected by ritonavir cotreatment (Fig. 2). The gMean terminal t of afatinib was unchanged (34.1 h with ritonavir vs. 35.9 h without ritonavir). Intra-individual
Table 1 Baseline characteristics of the male study populations Characteristic
Study 1 (n = 22)
Study 2 (n = 24)
Study 3 (n = 22)
Age (years)
38.2 ± 8.8 (21–49)
38.0 ± 8.3 (18–51)
32.7 ± 8.3 (22–48)
Weight (kg)
82.5 ± 9.4
87.0 ± 10.3
80.8 ± 7.4
BMI (kg/m2)
25.6 ± 2.1
26.0 ± 2.2
25.2 ± 1.7
Data shown as mean ± standard deviation (range) BMI body mass index
Afatinib plasma concentration [ng/mL]
Pharmacokinetic Drug Interactions of Afatinib
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100
10
1
0.1 0
12
24
36
48
60
72
84
96
108
120
Time [hours] Afatinib 20 mg (n=22)
Afatinib 20 mg + ritonavir (n=22)
Fig. 2 Geometric mean plasma concentrations of afatinib versus time after single oral administration of afatinib 20 mg alone or with ritonavir 200 mg to healthy male volunteers (semi-logarithmic scale)
comparisons of the exposure parameter AUC? between treatments show an increase in the majority of subjects when afatinib was given in combination with ritonavir (see Fig. S1 in the Electronic Supplementary Material 1). 3.2 Effect of Simultaneous and Timed Administration of Ritonavir on the Pharmacokinetics of Afatinib 40 mg Of 24 subjects enrolled in study 2, two discontinued due to adverse events (see Safety section for further details). Available data from all 24 subjects were included in the pharmacokinetic analysis. Plasma concentration–time profiles of afatinib were similar when given alone or with ritonavir (Fig. S2 in the Electronic Supplementary Material 1). Table 3 shows a comparison of gMean pharmacokinetic parameters of afatinib for the three treatment periods.
With simultaneous administration of ritonavir, gMean afatinib AUC? increased by 18.6 % (90 % CI for gMean ratio 1.117–1.258), and Cmax was within the standard bioequivalence limits (0.8–1.25) with an increase of 4.1 % (90 % CI for gMean ratio 0.967–1.120). Intra-individual variability was low [geometric coefficient of variation (gCV) values between 11.5 and 14.2 %]. With ritonavir administered 6 h later, afatinib pharmacokinetic parameters were completely within the bioequivalence limits: gMean afatinib AUC? increased by 10.8 % (90 % CI for gMean ratio 1.049–1.169), and Cmax increased by 5.1 % (90 % CI for gMean ratio 0.964–1.145). Intra-individual variability was low (gCV values between 10.0 and 16.1 %). Intra-individual comparisons between AUC? for the three treatments are shown in Fig. 3, and demonstrate that for most subjects, afatinib exposure was somewhat higher for administration of concomitant ritonavir or timed ritonavir than for afatinib alone. The tmax and gMean terminal t of afatinib was not affected by ritonavir (Table 3). 3.3 Effect of Rifampicin on the Pharmacokinetics of Afatinib 40 mg Twenty-two healthy male volunteers were enrolled in and completed study 3. The afatinib plasma concentration–time profile is shown in Fig. 4 (see Fig. S3 in the Electronic Supplementary Material 1 for linear scale) and pharmacokinetic parameters are summarised in Table 4. In combination with rifampicin, afatinib AUC? decreased by 33.8 % (90 % CI for gMean ratio 0.608–0.721), and Cmax decreased by 21.6 % (90 % CI for gMean ratio 0.724–0.850). Inter-individual variability of exposure parameters was moderate and similar for the two treatments (gCV values ranging from 32.1 to 39.8 %), and intra-individual variability was low (gCV
Table 2 Pharmacokinetic parameters of afatinib after single oral administration of afatinib 20 mg alone (reference), and together with ritonavir 200 mg twice-daily for 3 days, when the third ritonavir dose was administered 1 h before afatinib (test) Parameter and unit
Afatinib 20 mga Alone (n = 22) (reference)
? Ritonavir (n = 22) (test)
Adjusted gMean ratios (90 % CI)
Intra-individual gCV (%)
19.2
AUC? (ngh/mL)
165 (37.9)
243 (26.0)
1.476 (1.337–1.629)
AUClast (ngh/mL)
153 (39.7)
228 (27.1)
1.490 (1.345–1.651)
19.9
Cmax (ng/mL)
7.71 (47.4)
10.7 (30.0)
1.385 (1.206–1.589)
27.0
tmaxb (h)
4.0 (0.5–5.0)
4.0 (3.98–5.0)
t (h)
35.9 (25.1)
34.1 (16.8)
AUC? area under the plasma concentration–time curve from time zero to infinity, AUClast area under the plasma concentration–time curve from time zero to the last quantifiable drug plasma concentration, Cmax maximum observed plasma concentration, CI confidence interval, gCV (%) geometric coefficient of variation (%), gMean geometric mean, tmax time to reach Cmax, t terminal elimination half-life a
Results are presented as gMean (gCV%) unless specified
b
These values are expressed as median (range)
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Table 3 Pharmacokinetic parameters of afatinib after single oral administration of afatinib 40 mg alone (reference) and together with ritonavir 200 mg twice daily for 3 days, when the third ritonavir dose was administered together with (simultaneous) or 6 h after afatinib (timed) Parameter and unit
Afatinib 40 mga Alone (n = 22)
? Simultaneous ritonavir (n = 24)
? Timed ritonavir (n = 22)
Simultaneous ritonavir/afatinib alone
Timed ritonavir/afatinib alone
Adjusted gMean ratio (90 % CI)
Adjusted gMean ratio (90 % CI)
Intraindividual gCV (%)
Intraindividual gCV (%)
AUC? (ngh/mL)
426 (22.8)
515 (27.5)
475 (19.4)
1.186 (1.117–1.258)
11.5
1.108 (1.049–1.169)
10.0
AUClast (ngh/mL)
392 (26.2)b
478 (27.9)
438 (20.3)
1.193 (1.122–1.268)
11.5
1.102 (1.038–1.170)
10.9
Cmax (ng/mL)
19.5 (33.5)
20.7 (29.4)
20.7 (24.4)
1.041 (0.967–1.120)
14.2
1.051 (0.964–1.145)
16.1
tmaxc
(h)
t (h)
6.0 (4.0–8.0)
6.0 (3.0–8.0)
6.0 (0.5–8.0)
33.0 (25.8)
32.5 (18.2)
33.9 (24.5)
AUC? area under the plasma concentration–time curve from time zero to infinity, AUClast area under the plasma concentration–time curve from time zero to the last quantifiable drug plasma concentration, Cmax maximum observed plasma concentration, CI confidence interval, gCV (%) geometric coefficient of variation (%), gMean geometric mean, tmax time to reach Cmax, t terminal elimination half-life Results are presented as gMean (gCV%) unless specified
b
n = 21
c
These values are expressed as median (range)
Afatinib plasma concentration [ng/mL]
a
Afatinib AUC∞ [ng•h/mL]
900 750 600 450 300 150
100
10
1
0.1 0
12
24
36
0
48
60
72
84
96
108
120
Time [hours] Afatinib 40 mg (n=22)
Afatinib 40 mg + simultaneous ritonavir (n=24)
Individual data
Afatinib 40 mg + timed ritonavir (n=22)
gMean
Fig. 3 Intra-individual comparison of afatinib AUC? after single oral administration of 40 mg afatinib alone, together with 200 mg ritonavir (simultaneous), or 6 h before 200 mg ritonavir (timed). AUC? area under the plasma concentration–time curve from time zero to infinity, gMean geometric mean
values between 15.6 and 16.5 %). Intra-individual comparisons of AUC? demonstrated that for almost all subjects, exposure decreased for the test treatment compared with the reference treatment (Fig. 5). The median tmax and the gMean terminal t of afatinib were comparable between the treatments. Compared with day 1, the urinary 6-b-hydroxycortisol/ cortisol ratio was increased by approximately 4.5-fold after 7 days’ treatment with rifampicin, from a gMean (gCV) 6-b-hydroxycortisol/cortisol ratio of 5.02 (66.2 %) to 22.5 (61.7 %).
Afatinib 40 mg (n=22)
Afatinib 40 mg + rifampicin (n=22)
Fig. 4 Geometric mean plasma concentrations of afatinib versus time after single oral administration of afatinib 40 mg alone (reference) or after single oral administration of afatinib 40 mg after 7 days’ treatment with rifampicin 600 mg/day (test) (semi-logarithmic scale)
3.4 Safety Across the three trials, 36.4–83.3 % of healthy male subjects reported one or more adverse events. The most common adverse events with afatinib were diarrhoea and headache. Most adverse events were of mild or moderate intensity (National Cancer Institute Common Terminology Criteria for Adverse Events Version 3.0 grade 1 or 2) and no serious adverse events were reported. A total of 14 (21.5 %) subjects had possible drug-related adverse events. Eight of these subjects experienced diarrhoea (seven in combination with ritonavir) and three subjects were noted to have an increase in lipase concentration [3 times the upper limit of normal (ULN). Asymptomatic increase in
Pharmacokinetic Drug Interactions of Afatinib
179
Table 4 Pharmacokinetic parameters of afatinib after single oral administration of afatinib 40 mg alone (reference) or after single oral administration of afatinib 40 mg after 7 days treatment with rifampicin (rifampin) 600 mg/day (test) Parameter and unit
Afatinib 40 mga
Adjusted gMean ratios (90 % CI)
Intra-individual gCV (%)
Alone (n = 22) (reference)
? Rifampicin (n = 21) (test)
Cmax (ng/mL)
38.3 (38.4)
30.0 (34.1)b
0.784 (0.724–0.850)
15.6
AUC? (ngh/mL)
912 (38.3)
610 (32.1)
0.662 (0.608–0.721)
16.1
AUClast (ngh/mL) tmaxc (h)
860 (39.8) 6.0 (5.0–7.0)
575 (32.3) 6.0 (3.0–8.0)b
0.662 (0.607––0.722)
16.5
t (h)
32.8 (18.4)
36.0 (15.1)
AUC? area under the plasma concentration–time curve from time zero to infinity, AUClast area under the plasma concentration–time curve from time zero to the last quantifiable drug plasma concentration, Cmax maximum observed plasma concentration, CI confidence interval, gCV (%) geometric coefficient of variation (%), tmax time to reach Cmax, t terminal elimination half-life a Results are presented as gMean (gCV%) unless specified b
n = 22
c
These values are expressed as median (range)
confirmed no pathological findings. In addition, one subject in study 3 with an abnormal baseline lipase concentration developed a transient increase in lipase 3 9 ULN after a single dose of afatinib (40 mg), which returned to normal within 24 h. A further dose of afatinib in combination with rifampicin was given in the second treatment period without any increase in lipase concentration.
2250
Afatinib AUC∞ [ng•h/mL]
2000 1750 1500 1250 1000 750
4 Discussion
500 250 0 Afatinib 40 mg (n=22)
Individual data
Afatinib 40 mg + rifampicin (n=21)
gMean
Fig. 5 Intra-individual comparisons of afatinib AUC? for test (afatinib 40 mg after 7 days’ treatment with rifampicin 600 mg/ day) and reference (afatinib 40 mg alone) treatments. AUC? area under the plasma concentration–time curve from time zero to infinity, gMean geometric mean
gamma-glutamyltransferase [2 9 ULN and rash were experienced by a further one subject each, and one subject reported dizziness, headache, nausea and vomiting. Two subjects in study 2 were withdrawn from treatment because of asymptomatic lipase elevation (grade 4); one of these subjects received cumulative doses of afatinib 80 mg and ritonavir 1,400 mg and the other received afatinib 40 mg and ritonavir 1,200 mg. One subject had a lipase concentration 8 9 ULN, which returned to normal at follow-up. The other subject had a lipase concentration up to 11 9 ULN. Lipase levels remained elevated after discontinuation of study treatment and were accompanied by a mild increase in amylase (\3 9 ULN), although C-reactive protein was normal. An ultrasound of the pancreas
Preclinical investigations have demonstrated that afatinib is a substrate for the efflux transporter protein P-gp. Therefore, these three studies aimed to investigate the pharmacokinetic drug–drug interactions of afatinib during coadministration with a potent P-gp inhibitor (ritonavir) and potent inducer (rifampicin). The first study investigated the effect of P-gp inhibition on afatinib exposure. A dose of afatinib 20 mg was used as higher doses had not been tested in healthy volunteers at this timepoint in clinical development and the effect of P-gp inhibition on afatinib exposure was unknown. Ritonavir was used as P-gp inhibitor, as it has been identified as a highly potent inhibitor of both P-gp and CYP3A4 [13– 15], and is considered an appropriate P-gp inhibitor to estimate the maximum increase in exposure of a drug [16, 17]. In view of the short t for ritonavir (3–5 h) [18], twice-daily administration (200 mg) would likely result in steady-state levels 1 day after administration. In line with this, afatinib was administered on day 2 of the 3-day ritonavir treatment period, which was chosen to avoid any inductive effects described for this compound and thereby diminish the inhibitory effect on P-gp [19]. The rate and extent of absorption of afatinib were increased by coadministration with ritonavir by 47.6 % for
180 Fig. 6 Effect of ritonavir and rifampicin (rifampin) on afatinib exposure. AUC area under the plasma concentration– time curve, CI confidence interval, Cmax maximum plasma concentration
S. Wind et al. Reference
Test
Afatinib 20 mg
with ritonavir [-1 h]
Afatinib 40 mg
with ritonavir [0 h]
Afatinib 40 mg
with ritonavir [+6 h]
Afatinib 40 mg
with rifampicin 0.80
1.00
1.25
Test/reference ratio ± 90% CI AUC test/reference ratio ± 90% CI Cmax test/reference ratio ± 90% CI
AUC? and 38.5 % for Cmax, which can be classified as mild according to current guidelines [17]. However, ritonavir did not influence the time to Cmax or the distribution and elimination phases of afatinib. Previous studies have shown that CYP3A4 enzyme-catalysed metabolic reactions play a subordinate role in the metabolism of afatinib in vivo and CYP3A4-dependent N-demethylation is too low to be quantitatively detected in healthy volunteers [8]. Therefore, the increase in afatinib exposure in the presence of ritonavir can most likely be attributed to increased bioavailability resulting from inhibition of intestinal P-gp-mediated transport processes during the absorption phase of afatinib. The second study investigated the effect of P-gp inhibition with ritonavir (200 mg twice daily for 3 days) when administered simultaneously or 6 h after afatinib. This design was chosen to be clinically more meaningful (simultaneous administration with a P-gp inhibitor) and to define a dosing schedule for a safe combination of the clinically more relevant 40 mg dose of afatinib with a potent P-gp inhibitor. As both ritonavir treatments (either simultaneous or timed administration) had little influence on afatinib exposure (adjusted gMean ratios of AUC parameters and Cmax for afatinib were bioequivalent and well within 0.80–1.25; only the upper 90 % CI of AUC parameters for the simultaneous ritonavir administration was slightly above 1.25) (Fig. 6), it can be concluded that there was no clinically relevant drug–drug interaction with ritonavir. The negligible effects on afatinib exposure in this trial compared with study 1 are likely due to differences in the trial design. First, the effect of P-gp transport on afatinib bioavailability is likely to be lower for the 40 mg than the 20 mg dose, consistent with a known slight over-proportional increase in exposure over the afatinib dose range of 20–50 mg [7]. This non-linear behaviour could potentially be caused by saturation of the P-gp transporter, which would explain increased effects
of ritonavir at lower doses of afatinib. Second, the staggered dosing of ritonavir applied in study 2 may have contributed to the negligible effect; afatinib absorption is assumed to be mainly complete when ritonavir was administered 6 h later. In contrast, the first study had a ‘‘maximum inhibition scenario’’, in which ritonavir was administered 1 h before afatinib to ensure there was optimal inhibition of intestinal P-gp transport at the time of afatinib administration. This maximal P-gp inhibition might have been already impacted by simultaneous administration of afatinib with ritonavir. The change of two parameters, dose and administration schedule, in parallel between studies 1 and 2 may limit a definitive assessment about why the treatment effect in study 2 was lower than in study 1. The effect observed could have been due to the higher dose or the different timing of ritonavir administration, or a mixture of both. The third study investigated the effect of potent induction of P-gp expression by pre-treatment for 7 days with rifampicin, which induces a number of drug-metabolising enzymes, including intestinal and hepatic P-gp and CYP3A in the liver and in the small intestine [14, 15]. Full induction of P-gp is reached about 1 week after starting rifampicin treatment (600 mg daily) and the induction dissipates in roughly 2 weeks after discontinuing rifampicin [20]. Measurement of a surrogate endpoint, the urinary 6-b-hydroxycortisol/cortisol ratio, confirmed this effect [21, 22]. Pre-treatment with rifampicin moderately decreased the exposure to afatinib by 33.8 % (based on AUC) and by 21.6 % (based on Cmax). This effect is presumably related to elevated P-gp expression levels leading to an increased efflux transport of afatinib. As coadministration of rifampicin did not influence tmax or terminal t of afatinib, the effects may be mainly explained by a decreased fraction of afatinib reaching systemic circulation due to increased intestinal efflux transport.
Pharmacokinetic Drug Interactions of Afatinib
Taken together, observations from these three studies suggest that P-gp modulation mainly affects the extent of absorption of afatinib. Considering the effect size of P-gp induction or inhibition in relation to the variability in afatinib exposure, it can be inferred that coadministration with any P-gp inducer or inhibitor (potent, moderate or mild) would not require any adjustment to the starting dose of afatinib. Although other strong P-gp inhibitors (including but not limited to cyclosporine, erythromycin, ketoconazole, itraconazole, quinidine, valspodar, verapamil, tacrolimus, nelfinavir, saquinavir and amiodarone) have not been studied, pharmacologically, any interactions are likely to be similar to that for ritonavir [6]. In order to further reduce the risk of any interaction, it is recommended to administer strong P-gp inhibitors, using staggered dosing. A similar effect with the use of staggered dosing was observed for the oral anticoagulant dabigatran etexilate (a P-gp substrate) when coadministered with verapamil [23]. Besides P-gp interactions, other transporters that may have clinically important effects on the drug absorption and disposition of afatinib have been studied [24]. In vitro, afatinib is a substrate as well as an inhibitor of the breast cancer resistance protein (BCRP) ([12]). As ritonavir was shown to be an inhibitor of BCRP in vitro [25] and its exposure should have been sufficiently high to inhibit BCRP in studies 1 and 2 [26], it is assumed that any effects on afatinib exposure based on BCRP inhibition were covered in both studies. Therefore, afatinib exposure should be at maximum mildly, if at all, increased by BCRP inhibition. Single doses of afatinib were well-tolerated when given alone and in combination with multiple doses of rifampicin or ritonavir to healthy male volunteers. The adverse events were in line with the known safety profile of afatinib. In two subjects, combined administration of ritonavir and afatinib was associated with asymptomatic lipase increases of 8 and 11 9 ULN. The study design did not allow definitive assessment of whether the effects were related to ritonavir and/or afatinib, and the observed increases were therefore considered as possibly related to both medications. Pancreatitis is considered a common adverse effect of ritonavir [18] and in afatinib-treated patients lipase elevation/pancreatitis has been reported infrequently. We acknowledge a number of limitations in these studies. First, the subjects included in each of the studies were all healthy male Caucasian subjects. Sex and ethnic differences in the therapeutic response to drug treatment are well-recognised but difficult to predict due to the large number of genetic and environmental factors that may influence drug disposition [27]. However, exploratory analyses looking at genetic P-gp polymorphisms do not suggest any correlation, and any significant afatinib
181
exposure differences for race are not expected. Second, only single doses of afatinib were administered to all subjects. However, considering the over-proportional pharmacokinetics of afatinib in the therapeutic dose range of 20–50 mg, which are likely due to saturation of P-gp transport [7], it is expected that effects are more pronounced at lower, single doses. Thus, the effects of P-gp inhibition on afatinib exposure in patients after multiple dosing would be expected to be lower than in study 1 and be more in the range of study 2. In addition, multiple-dose administration of afatinib to healthy volunteers was not considered feasible due to the safety of the subjects. As the maximum effect of P-gp modulators was expected after single dosing of afatinib, the effects on afatinib exposure are over- rather than underestimated in the present studies, providing the most conservative approach for evaluation.
5 Conclusion Maximum inhibition or induction of P-gp as tested by coadministration of ritonavir and rifampicin had no clinically relevant effect on exposure to afatinib. Ritonavir administration simultaneously or 6 h after afatinib 40 mg had no relevant impact on afatinib exposure, indicating that P-gp inhibitors can be safely combined with afatinib while considering the timing of coadministration. The results of this study provide valuable information for the safe and effective use of afatinib in combination with potent P-gp inhibitors and inducers. As afatinib has no CYP liability and efflux transporter liability is mild and can be handled by timing of concomitant therapy, the drug–drug interaction potential of afatinib is considered to be low. Acknowledgments These studies were sponsored by Boehringer Ingelheim Pharma GmbH & Co. KG, Germany. The studies were conducted at the Human Pharmacology Centre, Boehringer Ingelheim Pharma GmbH & Co. KG, Biberach, Germany (principal investigator, Mario Iovino). Boehringer Ingelheim was responsible for the design and conduct of all of the studies, and the collection and management of the data. The authors were responsible for the analysis and interpretation of the data and the preparation of the manuscript. All authors are employees of Boehringer Ingelheim and were fully responsible for all content and editorial decisions, and were involved at all stages of the manuscript development.
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