Epilepsy Research (2014) 108, 909—916
journal homepage: www.elsevier.com/locate/epilepsyres
Reassessment of stiripentol pharmacokinetics in healthy adult volunteers Sophie Peigné a, Elisabeth Rey a,b, Marie-Emmanuelle Le Guern c, Olivier Dulac a,d, Catherine Chiron a, Gerard Pons a,b, Vincent Jullien a,b,∗ a
Inserm U1129, Paris, France; University Paris Descartes, PRES Sorbonne Paris Cité, France; CEA Gif-sur-Yvette, France b Service de Pharmacologie, Hôpital Européen Georges Pompidou, Paris, France c Laboratoires BIOCODEX, 7 avenue Gallieni, 94250 Gentilly, France d Service de Neuropédiatrie, Groupe Hospitalier Necker—Enfants Malades, 149 rue de Sèvres, 75015 Paris, France Received 6 December 2013; received in revised form 17 February 2014; accepted 16 March 2014 Available online 26 March 2014
KEYWORDS Stiripentol; Pharmacokinetics; Adults
Summary Because children who have been receiving stiripentol for the treatment of Dravet syndrome for more than 10 years are now becoming young adults, it is important to accurately characterize stiripentol pharmacokinetics in this age range. A double-blind placebo-controlled dose ranging study was therefore conducted to investigate the pharmacokinetics and tolerability of stiripentol in 12 healthy volunteers. Each subject received 3 single doses of stiripentol (500, 1000, and 2000 mg) separated by a wash-out period of 1 week. Pharmacokinetics of stiripentol was analyzed for each dose by non-compartmental analysis. Median area under the curve (AUC), terminal elimination half-life (t1/2,z ) and maximal concentration (Cmax ) were calculated for between-dose comparison. Safety was evaluated based on both clinical and biological criteria. Oppositely to previous results, there was no concentration rebounds in the elimination phase, which could be the consequence of the food intake. A more than proportional increase in the AUC was observed, associated with a significant increase in the t1/2,z , for increasing doses (median AUC of 8.3, 31 and 88 mg h/L, and median t1/2,z of 2, 7.7 and 10 h for the 500, 1000, and 2000 mg doses respectively), which confirmed the Michaelis—Menten pharmacokinetics of Stiripentol. However, dose-normalized Cmax did not significantly vary between doses. Median
∗ Corresponding author at: Service de Pharmacologie, Hôpital Européen Georges Pompidou, 20 rue Leblanc, 75015 Paris, France. Tel.: +33 1 56 09 39 77; fax: +33 1 56 09 39 93. E-mail address: [email protected] (V. Jullien).
http://dx.doi.org/10.1016/j.eplepsyres.2014.03.009 0920-1211/© 2014 Elsevier B.V. All rights reserved.
910
S. Peigné et al. Michaelis—Menten parameters were 117 mg/h for Vmax and 1.9 mg/L for Km. No safety concern was observed during the study. The present study allowed a better characterization of the disposition phase of stiripentol and confirmed its non-linear pharmacokinetic behaviour. Further pharmacokinetic/pharmacodynamic studies would be useful to determine the optimal dose of stiripentol for the treatment of Dravet patients in adulthood. © 2014 Elsevier B.V. All rights reserved.
Introduction Stiripentol is a major drug for the treatment of Dravet Syndrome, a highly pharmacoresistant epilepsy in childhood (Chiron and Dulac, 2011). Its efficacy in combination with valproate and clobazam was evidenced in a randomized placebo-controlled paediatric trial, and a dose of 50 mg/kg/day is now recommended in children (Chiron et al., 2000). Efficacy is persisting at long term, but since the patients are not seizure free, stiripentol tends to be maintained for a long time (Thanh et al., 2002). As a result, 13 years after this seminal study, stiripentol is now administered in young adults with persisting Dravet Syndrome, despite the fact that its pharmacokinetics is poorly understood in this population. The dose currently used in adults is the 50 mg/kg/day dose directly derived from paediatric studies. To date, three studies have investigated stiripentol pharmacokinetics in adults, in small series (6 subjects per study), two in healthy subjects, one in epileptic patients (Levy et al., 1983, 1984a,b). In these studies, stiripentol, administered as its capsule form, was found to follow a Michaelis—Menten kinetics with a decrease in its apparent clearance for increasing doses. However, stiripentol pharmacokinetics was also characterized by the presence of concentration rebounds during the elimination phase, which might have precluded an accurate description of its pharmacokinetics. For instance, because of this phenomenon, it was not possible to determine the terminal elimination half-life of the drug and only mean residence times were determined (Levy et al., 1984a,b). It seems important to check these results in order to verify whether an accurate description of stiripentol pharmacokinetics is possible. Achieving a satisfying exposure is probably mandatory because stiripentol is now known to act directly via the improvement of the GABAergic neurotransmission (Fisher, 2011), and not only via the pharmacokinetic enhancement of norclobazam (Giraud et al., 2006). Knowing the pharmacokinetics of stiripentol in the adult population is therefore a prerequisite for the optimization of stiripentol therapy in adult patients with Dravet syndrome. We report here PK data of stiripentol based on its 500 mg capsule dosage form in 12 healthy adults.
Materials and methods Subjects and treatments This study was conducted in one investigation centre: ASTER-CEPHAC, Paris, France, after approval had been obtained from the Ethics Committee of Ambroise-Paré Hospital (Boulogne-Billancourt, France).
Twelve non-smoking male healthy Caucasian volunteers were recruited. Subjects had to be between 18 and 40 years old, to drink less than 20 g of alcohol per day, to display no anomaly at clinical and biological examinations, and to have a BMI comprised between 18 and 28 and a QT interval ≤440 ms. Medical treatments within the 2 weeks prior to the theoretical day of inclusion were not allowed. All subjects had to sign an individual consent before inclusion in the study. Stiripentol (500 mg capsules) and the corresponding placebo were provided by Biocodex.
Study design A double-blind cross-over study with 3 different periods was performed. Each subject received, in a randomized design, 3 different doses of stiripentol: 500, 1000, and 2000 mg. Each dose was followed by a 1 week wash-out period. Each intake consisted of 4 tablets in order to be able to fulfil the doubleblind aspect of the study: for the 500, 1000 and 2000 mg doses the subjects received 1 tablet of stiripentol plus 3 tablets of placebo, 2 tablets of stiripentol plus 2 tablets of placebo, and 4 tablets of stiripentol respectively. The volunteers were hospitalized the day before each administration and stayed for at least 24 h each day of intake. They had to come back at the 30th hour for a blood sampling. The tablets were administered with 100 mL of water. Administrations occurred at 7 A.M. and subjects were fasted overnight. A breakfast was given before the intake, followed by lunch at 12.00, and dinner at 20.00. Pharmacokinetic study After each administration, blood samples (4 mL) were collected just before the intake (T0) and 0.33, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, 8, 10, 12, 18, 24 and 30 h after. Blood samples were immediately centrifuged and the plasma was stored at −20 ◦ C until analysis. Concentrations of stiripentol were measured in plasma by HPLC-UV method that was validated according to FDA guidelines. The lower limit of quantitation was 0.025 mg/L. Concentrations that were below the limit of quantification of the method (BLQ data) were substituted by zero if they corresponded to samples drawn before the first measurable concentration, and were treated as missing in other cases. Non-compartmental pharmacokinetic analysis was performed with WinNonlin 6.1 (Pharsight corporation). The following pharmacokinetic parameters were estimated: - The maximum observed concentration: Cmax , - The time corresponding to Cmax : tmax ,
Stiripentol pharmacokinetics - The terminal half-life: t1/2,z , calculated as follows:
t1/2,z =
ln 2 z
were z is the first order rate constant of the terminal phase calculated, using linear regression, as the slope of the terminal portion of the logarithmically transformed concentration—time curve. A minimum number of three data points (not including Cmax ) were required for the calculation of z. - The area under the concentration—time curve from zero (time of drug administration) to the time of the last quantifiable concentration (tlast ): AUClast . It was calculated using a combined linear and logarithmic trapezoidal rule; the interpolation is linear in the constant and ascending parts of the concentration—time profiles, while the interpolation is logarithmic in the descending parts.
911 - The area under the concentration—time curve from zero (time of drug administration) to infinity with extrapolation of the terminal phase: AUC. Extrapolation of AUC from the last observation to infinity, expressed as a percentage of the total AUC as follows: AUCext =
(AUC − AUClast ) × 100 AUC
if AUCext was greater than 20%, the corresponding AUC was reported but considered unreliable and not taken into account in statistical calculations. Such cases are flagged in the table with a comment: ‘‘Not taken into account in statistical calculations as AUCext > 20%’’. The maximum rate of elimination (Vm) and the Michaelis—Menten constant (Km) were determined for each subject by linear regression of AUC vs AUC normalized by dose (AUC/Dose). A squared coefficient of correlation
Figure 1 Mean (+SD) plasma concentration versus time profiles of Stiripentol after single oral administration of 500 (blue), 1000 (red) or 2000 (black) mg of Stiripentol. (A) Linear scale, (B) semi-logarithmic scale. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
tmax (h) Cmax (mg/L)
12 12 5.9 7.2 10 25 49 12 78 24 47 80 127 31 12 NA NA 1.0 3.0 3.0 —
12 8.3 3.6 3.3 7.7 15 43
12 2.6 1.4 1.1 2.0 6.3 56
12 8.8 3.7 3.7 8.3 15 42
12 6.6 1.8 3.9 6.5 10 28
12 NA NA 1.0 2.0 4.0 —
12 31 11 17 29 51 34
12 7.8 1.9 4.4 7.7 12 24
12 33 11 19 31 55 33 12 2.6 1.2 1.2 2.1 4.9 45
Cmax (mg/L) tmax (h)
AUClast (mg h/L)
t1/2,z (h)
AUC (mg h/L)
1000 mg
tmax (h)
AUClast (mg h/L)
t1/2,z (h)
N MEAN STD MIN MEDIAN MAX CV%
AUC (mg h/L)
2000 mg
Cmax (mg/L)
Oral administration of 500 mg of Stiripentol resulted in a median (range) of 3.0 (1.0—3.0) h for tmax , 2.0 (1.1—6.3) mg/L for Cmax , 7.7 (3.3—14.9) mg h/L for AUClast , 8.3 (3.7—15.3) mg h/L for AUC. The median (range) terminal elimination half-life, t1/2,z , of Stiripentol was 2 (1.1—6.25) h. Oral administration of 1000 mg of Stiripentol resulted in a median (range) of 2.0 (1.0—4.0) h for tmax , 6.5 (3.9—10.4) mg/L for Cmax , 29 (17.3—50.6) mg h/L for AUClast , 31 (18.6—55.5) mg h/L for AUC, 7.7 (4.4—11.8) h for t1/2,z . Oral administration of 2000 mg of Stiripentol resulted in a median (range) of 3.0 (1.5—4.0) h for tmax , 14.1 (8.3—24.0)
ID
PK study
500 mg
Twelve healthy volunteers were included in the study. Their mean (range) age was 29 (22—37) years, mean (range) weight was 78 (68—92) kg, mean (range) height was 180 (170—192) cm and mean (range) IMC was 24 (20—28) kg/m2 . All the subjects completed the study.
Dose
Subjects
Plasma pharmacokinetic parameters of Stiripentol after a 500, 1000 or 2000 mg single oral administration.
Results
Table 1
Statistical analysis Descriptive statistics (N, arithmetic mean, standard deviation (SD), minimum, median, maximum, coefficient of variation (CV) were used to summarize the PK parameters. Median, minimum and maximum only were calculated for tmax ) The possible influence of the order of administration of the 3 doses (sequence effect) on the following PK parameters: Cmax , tmax , AUC, t1/2,z , was investigated by a Kruskral—Wallis test with a significance level set at 0.05. The parameters used to compare exposure among doses were dose-normalized Cmax and AUC (Cmax /Dose, AUC/Dose) and t1/2,z . If the Kruskral—Wallis test was significant, Cmax /Dose, AUC/Dose, and t1/2,z were compared between the 1000 and 2000 mg doses by a Wilcoxon test for paired observations.
AUClast (mg h/L)
A clinical examination was performed during each day of hospitalization. Furthermore, blood pressure, heart rate and ECG (including QT interval) were measured just before and 1, 2, 3, 4, 12 and 24 h after the administration. Each subject had also to complete at the end of each period a questionnaire about the possible occurrence of adverse effects. Biological events were also investigated using the following parameters: haemoglobin, hematocrit, red and white blood cells count, thrombocytes count, blood ionogram, cholesterol and triglycerides level, glycaemia, blood proteins and hepatic enzymes.
12 NA NA 1.5 3.0 4.0 —
Safety assessment
12 14 4.8 8.3 14 24 35
t1/2,z (h)
AUC (mg h/L)
(r2 ) > 0.7 was required for the acceptance of this linear regression model. The values for Vm and Km corresponded to the slopes and the intercepts of the regression curves respectively.
N: Number if subjects; STD: standard deviation; Cmax : maximal concentration; tmax : time of the maximal concentration; AUClast : area under the curve from time zero to the last quantifiable concentration; t1/2,z : terminal elimination half-life; AUC: area under the curve extrapolated from time zero to infinity; NA: not applicable. a Denotes data from 2 subjects were not taken into account in statistical calculations because of an AUC ext > 20%.
S. Peigné et al.
10a 86 27 50 88 132 31
912
Stiripentol pharmacokinetics mg/L for Cmax , 80.5 (46.7—127) mg h/L for AUClast , 88.4 (49.8—132) mg h/L for AUC, 10.0 (7.2—24.9) h for t1/2,z . The order of administration of the 3 doses had no significant influence on the PK parameters. Mean plasma concentrations for each dose of stiripentol are displayed in Fig. 1 and the corresponding pharmacokinetic parameters are summarized in Table 1. AUCext was >20% at the 2000 mg dose for 2 subjects. The dosenormalized concentrations increased with the dose (Fig. 2). Cmax /Dose values were not significantly different between the three doses (Kruskal—Wallis test; p = 0.08), whereas AUC/Dose and t1/2,z were significantly different between the three doses (Kruskal—Wallis test; p = 5 × 10−05 and 2 × 10−06 respectively) (Fig. 3). AUC/Dose and t1/2,z were significantly different between the 1000 and 2000 mg doses (p = 0.002, and p = 0.012 respectively). The linear regressions of AUC vs AUC/Dose allowed an estimation of Vm and Km for all subjects but 1 (Table 2). Indeed, for this remaining subject, the linear regression
913 Table 2 Value of maximum rate of elimination (Vm) and Michaelis—Menten constant (Km). ID
Vmax (mg/h)
Km (mg/L)
N MEAN STD MIN MEDIAN MAX CV%
11 123 20 102 117 164 16
11 2.1 1.1 0.76 1.9 3.9 51
N: number of subjects; STD: Standard deviation.
model could not fit the observed data (r2 = 0.57). Thus, descriptive statistics were computed for 11 subjects instead of 12. The mean (± SD) r2 for these 11 subjects was 0.92 (± 0.08) and the mean (± SD) values for Vm and Km were 123 ± 20 mg/h and 2.1 ± 1.1 mg/L respectively.
Figure 2 Mean (+SD) dose-normalized plasma concentration versus time profiles of Stiripentol after single oral administration of 500 (blue), 1000 (red) or 2000 (black) mg of Stiripentol. (A) Linear scale, (B) semi-logarithmic scale. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
914
S. Peigné et al.
Figure 3
Dose-normalized Cmax (A), dose-normalized AUC (B), and t1/2,z with respect to the dose (C).
Safety Only two adverse effects (one rhinitis and one pharyngitis) were observed. The subjects completed the study and the relationship with the treatment was considered as unlikely. No clinical or biological change was observed during the study regarding arterial pressure, heart rate and ECG parameters (PR, QRS, QT, QTc), no modification was observed during the study.
Discussion The present study confirmed the Michaelis—Menten pharmacokinetic profile of stiripentol that was previously described in adult healthy volunteers and epileptic patients (Levy et al., 1983, 1984a,b; May et al., 2012). Nevertheless, stiripentol PK profile in the present study was not characterized by the occurrence of concentration rebounds in the elimination phase, which is different from what was previously described (Levy et al., 1983, 1984a,b). This lack of rebound allowed the calculation of stiripentol elimination half-life for each dose. The significant increase in this parameter from a dose to another is a supplemental
argument supporting a Michaelis—Menten pharmacokinetic behaviour for this drug. It is possible that the 2.0 h median elimination half-life obtained for the 500 mg dose was underestimated because some stiripentol concentrations were inferior to the LOQ of our method (0.025 mg/L) more than 10 h after drug intake. However, a significant increase in the terminal half-life was observed between the 1000 and 2000 mg doses, for which all the concentrations could be quantified. The median elimination half-lives obtained for the 1000 and 2000 mg doses (7.7 and 10 h) are higher than the mean residence times of about 4 h that were previously described for doses of 300, 600 and 1200 mg (Levy et al., 1983). Besides, our mean Cmax values for the 500 and 1000 mg doses (2.6 and 7.8 mg/L) seem higher than the values previously found in healthy subjects for the 600 and 1200 mg doses (1.6 and 3.43 mg/L) (Levy et al., 1983). These discrepancies are likely the consequence of the differences in the absorption profile of stiripentol observed in the present study, compared to what was described in the previous studies (Levy et al., 1983, 1984a,b). A possible explanation could consist in food intake which was allowed only 3 h after stiripentol in the study by Levy et al. (1983), whereas it
Stiripentol pharmacokinetics was permitted immediately before stiripentol in the present study (Levy et al., 1983). Our mean Vm, Km and Vm/Km ratio (2952 mg/day, 2.13 mg/L, and 1386 L/day) were nevertheless similar to the reported values in healthy volunteers (2299 mg/day, 2.20 mg/L, and 1241 L/day) (Levy et al., 1984a,b). The values of these parameters are known to be modified when stiripentol is combined to AEDs that are enzyme-inducers, like phenobarbitone, carabamazepine and phenytoin (Levy et al., 1984a,b). In the case of Dravet syndrome, stiripentol is frequently combined with valproate and clobazam which are not enzyme inducers and are not expected to significantly modify the pharmacokinetics of stiripentol. In a retrospective study based on therapeutic drug monitoring data, phenytoin and phenobarbitone decreased stiripentol concentrations by 63%, valproic acid had no influence on stiripentol concentrations, and clobazam slightly increased stiripentol concentrations by 25% (May et al., 2012). This latter result is not supported by theoretical considerations. Indeed, the main metabolic route of stiripentol, which is responsible for the transformation of 67% of the dose, involves CYP 450 enzymes that are not inhibited or induced by clobazam (Johannessen and Landmark, 2010; Moreland et al., 1986). Anyway, because the influence of clobazam on stiripentol PK is at best modest, the PK parameter values reported in the present work should be relevant for young adults receiving stiripentol for the treatment of Dravet syndrome. A surprising result was the lack of significant change in the Cmax/dose ratio between the 3 doses. In the context of a non-linear pharmacokinetic secondary to a saturable metabolism, a dose-related increase in the Cmax /dose ratio was indeed expected. However, such a result could be explained if stiripentol follows a zero-order absorption process (i.e. infusion-like profile). Absorption of stiripentol via an active transporter could lead to such a zero-order process. To date, as far as we know, the potential affinity of stiripentol to the currently known active transporters has not been investigated. Anyway, the fact the Cmax /dose ratio did not vary between doses suggests that the Cmax increased proportionally with dose and, since the linear model of AUC vs AUC/Dose satisfyingly fitted the individual data in 11 subjects (mean r2 = 0.92), it can be concluded that the bioavailability of stiripentol was not modified within the investigated dose range. So, the Vm and Km values we determined seem reliable to calculate the AUCs that would be obtained with doses
journal homepage: www.elsevier.com/locate/epilepsyres
Reassessment of stiripentol pharmacokinetics in healthy adult volunteers Sophie Peigné a, Elisabeth Rey a,b, Marie-Emmanuelle Le Guern c, Olivier Dulac a,d, Catherine Chiron a, Gerard Pons a,b, Vincent Jullien a,b,∗ a
Inserm U1129, Paris, France; University Paris Descartes, PRES Sorbonne Paris Cité, France; CEA Gif-sur-Yvette, France b Service de Pharmacologie, Hôpital Européen Georges Pompidou, Paris, France c Laboratoires BIOCODEX, 7 avenue Gallieni, 94250 Gentilly, France d Service de Neuropédiatrie, Groupe Hospitalier Necker—Enfants Malades, 149 rue de Sèvres, 75015 Paris, France Received 6 December 2013; received in revised form 17 February 2014; accepted 16 March 2014 Available online 26 March 2014
KEYWORDS Stiripentol; Pharmacokinetics; Adults
Summary Because children who have been receiving stiripentol for the treatment of Dravet syndrome for more than 10 years are now becoming young adults, it is important to accurately characterize stiripentol pharmacokinetics in this age range. A double-blind placebo-controlled dose ranging study was therefore conducted to investigate the pharmacokinetics and tolerability of stiripentol in 12 healthy volunteers. Each subject received 3 single doses of stiripentol (500, 1000, and 2000 mg) separated by a wash-out period of 1 week. Pharmacokinetics of stiripentol was analyzed for each dose by non-compartmental analysis. Median area under the curve (AUC), terminal elimination half-life (t1/2,z ) and maximal concentration (Cmax ) were calculated for between-dose comparison. Safety was evaluated based on both clinical and biological criteria. Oppositely to previous results, there was no concentration rebounds in the elimination phase, which could be the consequence of the food intake. A more than proportional increase in the AUC was observed, associated with a significant increase in the t1/2,z , for increasing doses (median AUC of 8.3, 31 and 88 mg h/L, and median t1/2,z of 2, 7.7 and 10 h for the 500, 1000, and 2000 mg doses respectively), which confirmed the Michaelis—Menten pharmacokinetics of Stiripentol. However, dose-normalized Cmax did not significantly vary between doses. Median
∗ Corresponding author at: Service de Pharmacologie, Hôpital Européen Georges Pompidou, 20 rue Leblanc, 75015 Paris, France. Tel.: +33 1 56 09 39 77; fax: +33 1 56 09 39 93. E-mail address: [email protected] (V. Jullien).
http://dx.doi.org/10.1016/j.eplepsyres.2014.03.009 0920-1211/© 2014 Elsevier B.V. All rights reserved.
910
S. Peigné et al. Michaelis—Menten parameters were 117 mg/h for Vmax and 1.9 mg/L for Km. No safety concern was observed during the study. The present study allowed a better characterization of the disposition phase of stiripentol and confirmed its non-linear pharmacokinetic behaviour. Further pharmacokinetic/pharmacodynamic studies would be useful to determine the optimal dose of stiripentol for the treatment of Dravet patients in adulthood. © 2014 Elsevier B.V. All rights reserved.
Introduction Stiripentol is a major drug for the treatment of Dravet Syndrome, a highly pharmacoresistant epilepsy in childhood (Chiron and Dulac, 2011). Its efficacy in combination with valproate and clobazam was evidenced in a randomized placebo-controlled paediatric trial, and a dose of 50 mg/kg/day is now recommended in children (Chiron et al., 2000). Efficacy is persisting at long term, but since the patients are not seizure free, stiripentol tends to be maintained for a long time (Thanh et al., 2002). As a result, 13 years after this seminal study, stiripentol is now administered in young adults with persisting Dravet Syndrome, despite the fact that its pharmacokinetics is poorly understood in this population. The dose currently used in adults is the 50 mg/kg/day dose directly derived from paediatric studies. To date, three studies have investigated stiripentol pharmacokinetics in adults, in small series (6 subjects per study), two in healthy subjects, one in epileptic patients (Levy et al., 1983, 1984a,b). In these studies, stiripentol, administered as its capsule form, was found to follow a Michaelis—Menten kinetics with a decrease in its apparent clearance for increasing doses. However, stiripentol pharmacokinetics was also characterized by the presence of concentration rebounds during the elimination phase, which might have precluded an accurate description of its pharmacokinetics. For instance, because of this phenomenon, it was not possible to determine the terminal elimination half-life of the drug and only mean residence times were determined (Levy et al., 1984a,b). It seems important to check these results in order to verify whether an accurate description of stiripentol pharmacokinetics is possible. Achieving a satisfying exposure is probably mandatory because stiripentol is now known to act directly via the improvement of the GABAergic neurotransmission (Fisher, 2011), and not only via the pharmacokinetic enhancement of norclobazam (Giraud et al., 2006). Knowing the pharmacokinetics of stiripentol in the adult population is therefore a prerequisite for the optimization of stiripentol therapy in adult patients with Dravet syndrome. We report here PK data of stiripentol based on its 500 mg capsule dosage form in 12 healthy adults.
Materials and methods Subjects and treatments This study was conducted in one investigation centre: ASTER-CEPHAC, Paris, France, after approval had been obtained from the Ethics Committee of Ambroise-Paré Hospital (Boulogne-Billancourt, France).
Twelve non-smoking male healthy Caucasian volunteers were recruited. Subjects had to be between 18 and 40 years old, to drink less than 20 g of alcohol per day, to display no anomaly at clinical and biological examinations, and to have a BMI comprised between 18 and 28 and a QT interval ≤440 ms. Medical treatments within the 2 weeks prior to the theoretical day of inclusion were not allowed. All subjects had to sign an individual consent before inclusion in the study. Stiripentol (500 mg capsules) and the corresponding placebo were provided by Biocodex.
Study design A double-blind cross-over study with 3 different periods was performed. Each subject received, in a randomized design, 3 different doses of stiripentol: 500, 1000, and 2000 mg. Each dose was followed by a 1 week wash-out period. Each intake consisted of 4 tablets in order to be able to fulfil the doubleblind aspect of the study: for the 500, 1000 and 2000 mg doses the subjects received 1 tablet of stiripentol plus 3 tablets of placebo, 2 tablets of stiripentol plus 2 tablets of placebo, and 4 tablets of stiripentol respectively. The volunteers were hospitalized the day before each administration and stayed for at least 24 h each day of intake. They had to come back at the 30th hour for a blood sampling. The tablets were administered with 100 mL of water. Administrations occurred at 7 A.M. and subjects were fasted overnight. A breakfast was given before the intake, followed by lunch at 12.00, and dinner at 20.00. Pharmacokinetic study After each administration, blood samples (4 mL) were collected just before the intake (T0) and 0.33, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, 8, 10, 12, 18, 24 and 30 h after. Blood samples were immediately centrifuged and the plasma was stored at −20 ◦ C until analysis. Concentrations of stiripentol were measured in plasma by HPLC-UV method that was validated according to FDA guidelines. The lower limit of quantitation was 0.025 mg/L. Concentrations that were below the limit of quantification of the method (BLQ data) were substituted by zero if they corresponded to samples drawn before the first measurable concentration, and were treated as missing in other cases. Non-compartmental pharmacokinetic analysis was performed with WinNonlin 6.1 (Pharsight corporation). The following pharmacokinetic parameters were estimated: - The maximum observed concentration: Cmax , - The time corresponding to Cmax : tmax ,
Stiripentol pharmacokinetics - The terminal half-life: t1/2,z , calculated as follows:
t1/2,z =
ln 2 z
were z is the first order rate constant of the terminal phase calculated, using linear regression, as the slope of the terminal portion of the logarithmically transformed concentration—time curve. A minimum number of three data points (not including Cmax ) were required for the calculation of z. - The area under the concentration—time curve from zero (time of drug administration) to the time of the last quantifiable concentration (tlast ): AUClast . It was calculated using a combined linear and logarithmic trapezoidal rule; the interpolation is linear in the constant and ascending parts of the concentration—time profiles, while the interpolation is logarithmic in the descending parts.
911 - The area under the concentration—time curve from zero (time of drug administration) to infinity with extrapolation of the terminal phase: AUC. Extrapolation of AUC from the last observation to infinity, expressed as a percentage of the total AUC as follows: AUCext =
(AUC − AUClast ) × 100 AUC
if AUCext was greater than 20%, the corresponding AUC was reported but considered unreliable and not taken into account in statistical calculations. Such cases are flagged in the table with a comment: ‘‘Not taken into account in statistical calculations as AUCext > 20%’’. The maximum rate of elimination (Vm) and the Michaelis—Menten constant (Km) were determined for each subject by linear regression of AUC vs AUC normalized by dose (AUC/Dose). A squared coefficient of correlation
Figure 1 Mean (+SD) plasma concentration versus time profiles of Stiripentol after single oral administration of 500 (blue), 1000 (red) or 2000 (black) mg of Stiripentol. (A) Linear scale, (B) semi-logarithmic scale. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
tmax (h) Cmax (mg/L)
12 12 5.9 7.2 10 25 49 12 78 24 47 80 127 31 12 NA NA 1.0 3.0 3.0 —
12 8.3 3.6 3.3 7.7 15 43
12 2.6 1.4 1.1 2.0 6.3 56
12 8.8 3.7 3.7 8.3 15 42
12 6.6 1.8 3.9 6.5 10 28
12 NA NA 1.0 2.0 4.0 —
12 31 11 17 29 51 34
12 7.8 1.9 4.4 7.7 12 24
12 33 11 19 31 55 33 12 2.6 1.2 1.2 2.1 4.9 45
Cmax (mg/L) tmax (h)
AUClast (mg h/L)
t1/2,z (h)
AUC (mg h/L)
1000 mg
tmax (h)
AUClast (mg h/L)
t1/2,z (h)
N MEAN STD MIN MEDIAN MAX CV%
AUC (mg h/L)
2000 mg
Cmax (mg/L)
Oral administration of 500 mg of Stiripentol resulted in a median (range) of 3.0 (1.0—3.0) h for tmax , 2.0 (1.1—6.3) mg/L for Cmax , 7.7 (3.3—14.9) mg h/L for AUClast , 8.3 (3.7—15.3) mg h/L for AUC. The median (range) terminal elimination half-life, t1/2,z , of Stiripentol was 2 (1.1—6.25) h. Oral administration of 1000 mg of Stiripentol resulted in a median (range) of 2.0 (1.0—4.0) h for tmax , 6.5 (3.9—10.4) mg/L for Cmax , 29 (17.3—50.6) mg h/L for AUClast , 31 (18.6—55.5) mg h/L for AUC, 7.7 (4.4—11.8) h for t1/2,z . Oral administration of 2000 mg of Stiripentol resulted in a median (range) of 3.0 (1.5—4.0) h for tmax , 14.1 (8.3—24.0)
ID
PK study
500 mg
Twelve healthy volunteers were included in the study. Their mean (range) age was 29 (22—37) years, mean (range) weight was 78 (68—92) kg, mean (range) height was 180 (170—192) cm and mean (range) IMC was 24 (20—28) kg/m2 . All the subjects completed the study.
Dose
Subjects
Plasma pharmacokinetic parameters of Stiripentol after a 500, 1000 or 2000 mg single oral administration.
Results
Table 1
Statistical analysis Descriptive statistics (N, arithmetic mean, standard deviation (SD), minimum, median, maximum, coefficient of variation (CV) were used to summarize the PK parameters. Median, minimum and maximum only were calculated for tmax ) The possible influence of the order of administration of the 3 doses (sequence effect) on the following PK parameters: Cmax , tmax , AUC, t1/2,z , was investigated by a Kruskral—Wallis test with a significance level set at 0.05. The parameters used to compare exposure among doses were dose-normalized Cmax and AUC (Cmax /Dose, AUC/Dose) and t1/2,z . If the Kruskral—Wallis test was significant, Cmax /Dose, AUC/Dose, and t1/2,z were compared between the 1000 and 2000 mg doses by a Wilcoxon test for paired observations.
AUClast (mg h/L)
A clinical examination was performed during each day of hospitalization. Furthermore, blood pressure, heart rate and ECG (including QT interval) were measured just before and 1, 2, 3, 4, 12 and 24 h after the administration. Each subject had also to complete at the end of each period a questionnaire about the possible occurrence of adverse effects. Biological events were also investigated using the following parameters: haemoglobin, hematocrit, red and white blood cells count, thrombocytes count, blood ionogram, cholesterol and triglycerides level, glycaemia, blood proteins and hepatic enzymes.
12 NA NA 1.5 3.0 4.0 —
Safety assessment
12 14 4.8 8.3 14 24 35
t1/2,z (h)
AUC (mg h/L)
(r2 ) > 0.7 was required for the acceptance of this linear regression model. The values for Vm and Km corresponded to the slopes and the intercepts of the regression curves respectively.
N: Number if subjects; STD: standard deviation; Cmax : maximal concentration; tmax : time of the maximal concentration; AUClast : area under the curve from time zero to the last quantifiable concentration; t1/2,z : terminal elimination half-life; AUC: area under the curve extrapolated from time zero to infinity; NA: not applicable. a Denotes data from 2 subjects were not taken into account in statistical calculations because of an AUC ext > 20%.
S. Peigné et al.
10a 86 27 50 88 132 31
912
Stiripentol pharmacokinetics mg/L for Cmax , 80.5 (46.7—127) mg h/L for AUClast , 88.4 (49.8—132) mg h/L for AUC, 10.0 (7.2—24.9) h for t1/2,z . The order of administration of the 3 doses had no significant influence on the PK parameters. Mean plasma concentrations for each dose of stiripentol are displayed in Fig. 1 and the corresponding pharmacokinetic parameters are summarized in Table 1. AUCext was >20% at the 2000 mg dose for 2 subjects. The dosenormalized concentrations increased with the dose (Fig. 2). Cmax /Dose values were not significantly different between the three doses (Kruskal—Wallis test; p = 0.08), whereas AUC/Dose and t1/2,z were significantly different between the three doses (Kruskal—Wallis test; p = 5 × 10−05 and 2 × 10−06 respectively) (Fig. 3). AUC/Dose and t1/2,z were significantly different between the 1000 and 2000 mg doses (p = 0.002, and p = 0.012 respectively). The linear regressions of AUC vs AUC/Dose allowed an estimation of Vm and Km for all subjects but 1 (Table 2). Indeed, for this remaining subject, the linear regression
913 Table 2 Value of maximum rate of elimination (Vm) and Michaelis—Menten constant (Km). ID
Vmax (mg/h)
Km (mg/L)
N MEAN STD MIN MEDIAN MAX CV%
11 123 20 102 117 164 16
11 2.1 1.1 0.76 1.9 3.9 51
N: number of subjects; STD: Standard deviation.
model could not fit the observed data (r2 = 0.57). Thus, descriptive statistics were computed for 11 subjects instead of 12. The mean (± SD) r2 for these 11 subjects was 0.92 (± 0.08) and the mean (± SD) values for Vm and Km were 123 ± 20 mg/h and 2.1 ± 1.1 mg/L respectively.
Figure 2 Mean (+SD) dose-normalized plasma concentration versus time profiles of Stiripentol after single oral administration of 500 (blue), 1000 (red) or 2000 (black) mg of Stiripentol. (A) Linear scale, (B) semi-logarithmic scale. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of the article.)
914
S. Peigné et al.
Figure 3
Dose-normalized Cmax (A), dose-normalized AUC (B), and t1/2,z with respect to the dose (C).
Safety Only two adverse effects (one rhinitis and one pharyngitis) were observed. The subjects completed the study and the relationship with the treatment was considered as unlikely. No clinical or biological change was observed during the study regarding arterial pressure, heart rate and ECG parameters (PR, QRS, QT, QTc), no modification was observed during the study.
Discussion The present study confirmed the Michaelis—Menten pharmacokinetic profile of stiripentol that was previously described in adult healthy volunteers and epileptic patients (Levy et al., 1983, 1984a,b; May et al., 2012). Nevertheless, stiripentol PK profile in the present study was not characterized by the occurrence of concentration rebounds in the elimination phase, which is different from what was previously described (Levy et al., 1983, 1984a,b). This lack of rebound allowed the calculation of stiripentol elimination half-life for each dose. The significant increase in this parameter from a dose to another is a supplemental
argument supporting a Michaelis—Menten pharmacokinetic behaviour for this drug. It is possible that the 2.0 h median elimination half-life obtained for the 500 mg dose was underestimated because some stiripentol concentrations were inferior to the LOQ of our method (0.025 mg/L) more than 10 h after drug intake. However, a significant increase in the terminal half-life was observed between the 1000 and 2000 mg doses, for which all the concentrations could be quantified. The median elimination half-lives obtained for the 1000 and 2000 mg doses (7.7 and 10 h) are higher than the mean residence times of about 4 h that were previously described for doses of 300, 600 and 1200 mg (Levy et al., 1983). Besides, our mean Cmax values for the 500 and 1000 mg doses (2.6 and 7.8 mg/L) seem higher than the values previously found in healthy subjects for the 600 and 1200 mg doses (1.6 and 3.43 mg/L) (Levy et al., 1983). These discrepancies are likely the consequence of the differences in the absorption profile of stiripentol observed in the present study, compared to what was described in the previous studies (Levy et al., 1983, 1984a,b). A possible explanation could consist in food intake which was allowed only 3 h after stiripentol in the study by Levy et al. (1983), whereas it
Stiripentol pharmacokinetics was permitted immediately before stiripentol in the present study (Levy et al., 1983). Our mean Vm, Km and Vm/Km ratio (2952 mg/day, 2.13 mg/L, and 1386 L/day) were nevertheless similar to the reported values in healthy volunteers (2299 mg/day, 2.20 mg/L, and 1241 L/day) (Levy et al., 1984a,b). The values of these parameters are known to be modified when stiripentol is combined to AEDs that are enzyme-inducers, like phenobarbitone, carabamazepine and phenytoin (Levy et al., 1984a,b). In the case of Dravet syndrome, stiripentol is frequently combined with valproate and clobazam which are not enzyme inducers and are not expected to significantly modify the pharmacokinetics of stiripentol. In a retrospective study based on therapeutic drug monitoring data, phenytoin and phenobarbitone decreased stiripentol concentrations by 63%, valproic acid had no influence on stiripentol concentrations, and clobazam slightly increased stiripentol concentrations by 25% (May et al., 2012). This latter result is not supported by theoretical considerations. Indeed, the main metabolic route of stiripentol, which is responsible for the transformation of 67% of the dose, involves CYP 450 enzymes that are not inhibited or induced by clobazam (Johannessen and Landmark, 2010; Moreland et al., 1986). Anyway, because the influence of clobazam on stiripentol PK is at best modest, the PK parameter values reported in the present work should be relevant for young adults receiving stiripentol for the treatment of Dravet syndrome. A surprising result was the lack of significant change in the Cmax/dose ratio between the 3 doses. In the context of a non-linear pharmacokinetic secondary to a saturable metabolism, a dose-related increase in the Cmax /dose ratio was indeed expected. However, such a result could be explained if stiripentol follows a zero-order absorption process (i.e. infusion-like profile). Absorption of stiripentol via an active transporter could lead to such a zero-order process. To date, as far as we know, the potential affinity of stiripentol to the currently known active transporters has not been investigated. Anyway, the fact the Cmax /dose ratio did not vary between doses suggests that the Cmax increased proportionally with dose and, since the linear model of AUC vs AUC/Dose satisfyingly fitted the individual data in 11 subjects (mean r2 = 0.92), it can be concluded that the bioavailability of stiripentol was not modified within the investigated dose range. So, the Vm and Km values we determined seem reliable to calculate the AUCs that would be obtained with doses
