Eur J Clin Pharmacol (1990) 38:71-75
P[bQQc@e® @ Spfinger-Verlag 1990
Pharmacokinetics of ( + )-rolipram and ( - )-rolipram in healthy volunteers W. K r a u s e , G. Ktthne, a n d N. S a u e r b r e y Research Laboratories of Schering AG, Berlin, Federal Republic of Germany
Summary. Plasma levels of S-( + )-rolipram and R-( - )rolipram in six healthy male volunteers were m e a s u r e d by r a d i o i m m u n o a s s a y after intravenous injection of 0.1 m g and oral administration of 1.0 m g of the pure enantionmers. Following i.v. treatment, plasma levels of b o t h isomers declined in three phases, with half-lives of 0.2 h, 0.64).9 h and 6-8 h. Total clearance was 6 ml. min -~-kg -~. Oral administration of 1.0 m g gave a p e a k c o n c e n t r a t i o n of 16 ng- m l - 1 after 0.5 h. Bioavailability of ( + )-rolipram was 77% and of the ( - ) e n a n t i o m e r it was 74%. T h e r e was no significant difference in Cmax, halflife, total clearance or bioavaflability b e t w e e n the two enantiomers. Key words: Rolipram; enantiomers, pharmacokinetics, healthy volunteers
R o l i p r a m ( I U P A C name: 4-(3-cyclopentyloxy-4-methoxy-phenyl)-2-pyrrolidone) is a selective c A M P phosphodiesterase inhibitor [1, 2], which has been shown to be effective in the t r e a t m e n t of e n d o g e n o u s depression [3, L a e m m e l and Sastre, 1983 unpublished data, 4]. D o p a m i n e r g i c and serotoninergic effects were not o b s e r v e d [5]. The drug was well tolerated without affecting heart rate, b l o o d pressure or o t h e r vital functions. R o l i p r a m is used as the racemate. However, in animal p h a r m a c o l o g y it has b e e n d e m o n s t r a t e d that only the R( - ) - e n a n t i o m e r is the carrier of phosphodiesterase inhibiting activity, and that the S-( + )-isomer is practically devoid o f this p r o p e r t y [6]. T h e r a c e m a t e was administered in previous p h a r m a cokinetic studies in animals and in m a n [7-9], as was the case in all the clinical investigations. T h e aim of the present study was to c o m p a r e the absorption and disposition of the two e n a n t i o m e r s in healthy male volunteers after separate administration of the two pure rolipram isomers.
Materials and methods
Experimental Design Six healthy male volunteers (age 31 (4) y, range 27-37 y; weight 71 (7) kg, range 59-79 kg; height 185 (9) cm, range t73-198 cm) participated in the study. They gave their written informed consent to it beforehand. All volunteers received 0.1 m g ( + )-rolipram and 0.1 m g ( - )rolipram intravenously and 1.0 mg ( + )-rolipram and 1.0 mg ( - )rolipram orally, according to an open randomized cross-over design, with a 2-week interval between treatments. For intravenous injection, rolipram was dissolved in bidist, water with 20% (by weight) propylene glycol at the concentration of 0.1mg.m1-1. For oral use, microcrystalline suspensions in Myrj/physiological saline (0.1 mg/ml) were prepared. All rolipram administrations were performed in the morning, after an overnight fast. Alcohol and caffeine were not allowed. Two weeks before and during the study any comedication was strictly excluded. Blood was collected from an arm vein contralateral to that used for the i.v. injection immediately before the administration of rotipram and 5, 10, 15, 20, 30, 45, 60 and 90 min, and 2, 3, 4, 5, 6, 8, 10, 22 and 24 h after i. v. treatment, and 15, 30, 45, 60 and 90 rain and 2, 3, 4, 6, 8, 10, 12 and 24 h after oral dosing. The plasma was immediately frozen at - 18°C until analyzed.
Methods The concentration of (+)- or (-)-rolipram in plasma was determined by radioimmunoassay. Plasma 0.05-0.2ml was extracted with 2.5 ml diethyl ether after adding saline to give a final sample volume of 0.5 ml. The ether phase was taken to dryness and the residue was redissolved in i ml aqueous bovine serum albumin solution (0.1%, w/v). After incubation with tracer and antiserum (dilution 1:250000) for 16 h at room temperature, bound and unbound fractions were separated with a charcoal suspension containing 5% dextran. After centrifugation, radioactivity was measured in the solution. Calibration was done by constructing a standard curve parallel to the unknown samples. Intra- and inter-assay variability was below 3% and 7%, respectively. The detection limit was 0.1 ng/ml. Because the antiserum had been obtained by immunization of rabbits with
72
W. Krause et al.: Rolipram kinetics
Concentration (ng/ml) 7r-
2~
Fig. 1. Plasma levels (mean and SD) of ( + )-rolipram ( x ) and ( - )-rolipram ( • ) in six healthy male volunteers after i.v. injection of 0.1 mg pure enantiomer
i
I Or o
I
I
h
0.5
1
1.5
2
2.5
3
Time
(h)
3.5
4
4.15
5.5
5
racemic rolipram-3-carboxylic acid coupled to bovine serum albumin, it did not discriminate between the two rolipram enantiomers.
Calculations Pharmacokinetic parameters (half-life, area under the plasma level-time curve (AUC), clearance, and volume of distribution) were calculated by the computer program TOPFIT, using a threecompartment body model. Bioavailability was evaluated by comparing AUC data after p.o. and i.v. administration and correcting for dose. Statistical differences were evaluated by Student's t test for paired data.
or 8.4 h ( - ), respectively. T h e m e a n transit time of ( + )or ( - )-rolipram was 2.7 h and 1.5 h, respectively. F r o m the area under the p l a s m a level-time curve ( A U C ) of 4.2 ( + ) or 4.3 h . n g - m 1 - 1 ( - ) , the total clearance of 6.5 ( + ) or 6.1 ml. m i n - 1. kg 1 ( _ ) was calculated. M e a n p l a s m a levels of the two e n a n t i o m e r s are illustrated in Fig. 1. T h e p h a r m a c o k i n e t i c p a r a m e t e r s of the ( + ) - and ( - ) - e n a n t i o m e r s of r o l i p r a m did not differ significantly except for the initial drug concentration after injection (P < 0.01; Figs.2, 3).
Plasma levels after p. o. administration
Results Plasma levels after i. v. injection A f t e r intravenous injection of ( + )- or ( - )-rolipram, the p l a s m a concentration of the drug declined in three phases (Table 1), with half-lives of 0.16 h (Phase I, both enantiomers), 0.6 h ( + ) or 0.9 h ( - ), and 5.7 h ( + )
B o t h e n a n t i o m e r s of rolipram were rapidly absorbed, achieving p e a k concentrations in p l a s m a of 16 ng/ml after 0.4 ( + ) or 0.5 h ( - ). Thereafter, plasma levels declined in three phases, with half-lives of 0.1 h (Phase I, ( + ) and ( - )), 0.4 h ( + ) or 0.5 h ( - ) (Phase II) and 4.6 h ( + ) or 9.4 h ( - ) (Phase III). M e a n transit time was 3.2 h ( + ) or 4.1h(-).
Table 1. Comparison of mean ( + SD) pharmacokinetic parameters of ( + )- and ( - )-rolipram in 6 healthy male volunteers after i. v. injection of 0.1 mg and p. o. administration of 1.0 mg pure enantiomer i. v. Admin. ( + )-Rolipram Cmax(ng/ml)
3.9
tmax ( h )
-
ha(abs-) (h) tl/2(I)(h) tla(II)(h) tl~ (III) (h) AUC(h.ng-m1-1) AUC(I)(%) AUC(II)(%) AUC(III) (%) V,~(1-kg-:) MTT (h) CL (ml. min - ~.kg- i) Bioavail. (%)
0.16 0.60 5.7 4.24 10.7 57.4 32.0 0.82 2.7 6.5 100
(1.0)
( - )-Rolipram 5.6
(1.2)
-
(0.09) (0.20) (4.0) (2.02) (12.4) (19.7) (23.6) (0.51) (2.9) (2.5) (0)
0.16 0.92 8.4 4.27 21.4 74.8 3.9 0.52 1.5 6.1 100
(0.08) (0.30) (0.2) (1.46) (13.2) (10.1) (5.3) (0.18) (0.5) (2.2) (0)
p.o. Admin. ( + )-Rolipram
( - )-Rolipram
15.7
(5.2)
16.4
(5.1)
0.4
(0.1)
0.5
(0.3)
0.25 0.13 0.62 4.6 29.2 12.1 53.9 33.9 3.2 77
(0.29) (0.12) (0.21) (3.2) (7.81) (11.0) (15.7) (8.7)
0.22 0.13 0.87 9.4 28.9 19.5 57.9 22.6 4.1 74
(0.23) (0.19) (0.51) (7.8) (7.92) (16.9) (18.2) (5.4)
(2.2) (32)
(2.9) (31)
73
W. Krause et al.: Rolipram kinetics Clearance (ml/min/kg) 10,
Fig.2. Total clearance of ( + )-rolipram ( 1 ) and
( - )-rolipram ( [ ] ) in six healthy male volunteers after i. v. injection of 0.1 mg pure entantiomer 1
2
3
4
5
6
Subject No.
1,6 r
a''l
o,8
n
0,6 T
0,4
0,2 0
1
2
3
4
5
6
I
lO
b "~
8
¢
6
,c
4
7-
Fig.3. Half-lives of disposition Phases II (top) and IfI (bottom) of ( + )-rolipram and ( - )-rolipram in six healthy male volunteers after i.v. injection of 0.1 mg pure enantiomer. Key as in Fig. 1
2
T
o
1
2
4
3
Subject
5
6
No.
Concentration (ng/ml) 25 I
20
15
10
0
.
0
2
4
.
.
.
6
Time (h)
•
8
10
Fig.4. Plasma levels (mean and SD) of ( + )-rolipram ( x ) and ( - )-rolipram ( • ) in six healthy male volunteers after p. o. administration of 1.0 mg pure enantiomer
"
12
14
74
W. Krause et al.: Rolipram kinetics
30,
Cmax (ng/ml)
25 20
15 10
Fig.5. Peak plasma level of ( + )-rolipram and ( - )-rolipram in six healthy male volunteers after p. o. administration of 1.0 mg pure enantiomer. Key as in Fig. 1
5 0
1
3
2
4
Subject No. Bioavailability (%) 160~
I
14o I 120 100
80 60
Fig.6. Bioavailability of ( + )-rolipram and ( - )-rolipram in six healthy male volunteers after p. o. administration of 1.0 mg pure enantiomer. Key as in Fig. 1
40 20 0 1
2
3
4
5
S u b j e c t No. From an A U C of 29 h-ng. ml 1, bioavailability was calculated as 77% ( + ) or 74% ( - ). Mean plasma levels are illustrated in Fig.4. Except for the partial area of disposition Phase III (0.01 < P < 0.05), the pharmacokinetic parameters of ( + )- and ( - )-rolipram were not significantly different (Figs. 5, 6). Discussion The aim of the present study was to investigate whether there were any differences in the absorption and disposition of the two enantiomers of rolipram. Only the ( - )form possesses antidepressant activity. Six healthy male volunteers were treated separately with each of the two isomers intravenously in the dose of 0.1 rag, and orally with 1.0 mg. The study followed an open randomized four-way cross-over design. Plasma levels of rolipram were determined by radioimmunoassay with an antiserum which had been raised against the racemate and therefore did not differentiate between the two enantiomers. Except for the starting concentration after i.v. injection, and for the partial area of disposition Phase III after p.o. treatment, statistical evaluation did not reveal any significant difference in the pharmacokinetic parameters of the two forms of rolipram. Neither difference is relevant to the estimation of the safety or efficacy of rolipram. Starting concentrations after i.v. injection strongly depend on the exact timing of
the duration of injections and on identical (within seconds) timing of the first sampling point. Terminal partial areas are strongly influenced by the sensitivity and reproducibility of the analytical method used. In the present study radioimmunoassay was employed and plasma levels were followed until the limit of detection was reached. Near that limit, data are necessarily subject to decreased precision and accuracy, which will strongly influence the last part of the terminal phase. The bioavailability of rolipram was 50-80% in five volunteers, and one other subject had values of 130 to 140% for both enantiomers. A possible reason for the discrepancy is non-linearity of rolipram kinetics, but that was only apparent in the one volunteer, or a decreased metabolizing capacity for rolipram, due either to hepatic insufficiency or to a difference in the metabolic phenotype (poor/extensive metabolizers). Hepatic insufficiency can be excluded, because all the volunteers were extensively checked, including liver funtion tests, prior to and after the study. Whether the metabolic phenotype (oxidizing capacity) is of importance in the pharmacokinetic handling of rolipram is not known. As a result of the present investigation, the pharmacokinetics of rolipram can adequately be described by the kinetic parameters of the racemate after correction for dose. It will not be necessary to measure separate plasma levels of the pharmacologically active ( - )-enantiomer in future studies.
75
w. Krause et al.: Rolipram kinetics Chiral p h a r m a c o l o g y and pharmacokinetics have gained considerably in i m p o r t a n c e in recent years [10-13]. T h e r e are three principal aspects of chirality in p h a r m a cotherapy. • Enantioselective drug action • Enantioselective p h a r m a c o k i n e t i c s / b i o t r a n s f o r m a t i o n • Interaction of e n a n t i o m e r s - at the r e c e p t o r level - kinetic/metabolic interaction Enantioselective drug action requires that the center of chirality in the molecule interacts with the receptor, causing differential efficacy of the two enantiomers. Examples of this type of drug are rolipram, ~3-blockers, such as labetalol [14, 15] and m e d r o x a l o l [16], and thalidomide which exerts a teratogenic action exclusively t h r o u g h the ( - )enantiomer, as the ( + ) - a n t i p o d e is inactive [17]. E n a n tioselective p h a r m a c o k i n e t i c s and/or biotransformation have b e e n r e p o r t e d for p r o p a n o l o l [18, 19], m e t h a c h o l i n [20] and verapamil [21]. T h e interaction of e n a n t i o m e r s has b e e n o b s e r v e d for barbiturates, where ( + ) isomers m a y cause central n e r v o u s system excitation, and the ( - )isomers are sedative [22], and for s o m e p s y c h o m i m e t i c amines, w h e r e the presence of one e n a n t i o m e r effectively inhibited the m e t a b o l i s m of the other [23]. T h e use of racemic drugs in t h e r a p y has b e e n questioned for all these reasons [12, 24]. However, as long as there is no selective side-effect of the pharmacologically "inactive" antipode, no interaction of the two enantiomers, and w h e n e v e r the p h a r m a c o k i n e t i c s of the "active" isomer can easily be determined, for example by stereoselective analysis, there should be no obj ection to the introduction of racemic mixtures. In the case of rolipram, due to the identical p h a r m a c o k i n e t i c b e h a v i o u r of the two antipodes, not even stereoselective analysis should be necessary. Interaction at the kinetic/metabolic level appears unlikely, because the chiral center is not attacked during biot r a n s f o r m a t i o n [Krause and Kfihne, 1987, unpublished data], and, in addition, the clearance rates of the enantiomers are identical w h e n t h e y are given separately. T h e p h a r m a c o k i n e t i c s of the active isomer of rolipram, therefore, can adequately be described by the parameters of the r a c e m a t e after correction for dose.
Acknowledgement. Synthesis of the ( + )- and ( - ) isomers of rolipram by Dr. R. Schmiechen is gratefully acknowledged.
References 1. Wachtel H (1982) Characteristic behavioural alteration in rats induced by rolipram and other selective adenosine cyclic 3', 5'monophosphate phosphodiesterase inhibitors. Psychopharmacotogy 77:30%316 2. Wachtel H (1983) Potential antidepressant activity of rolipram and other selective cyclic adenosine 3', 5'-monophosphate phosphodiesterase inhibitors. Neuropsychopharmacology 22: 267272 3. Horowski R, Sastre M (1985) Clinical effects of the neurotropic selective cAMP phosphodiesterase inhibitor rolipram in depressed patients: Global evaluation of the preliminary reports. Current Ther Res 38:23-29
4. Zeller E, Stief H J, Pflug B, Sastre-y-Hernandez M (1984) Results of a phase II study of the antidepressant effect of rolipram. Pharmacopsychiatry 17:188-190 5. Przegalinski E, Bigajska K, Lewandowska A (1981) The influence of rolipram in the central serotoninergic system. Pharmacopsychiatry 14:162-166 6. Schultz JE, Schmidt B H (1986) Rolipram, a stereospecific inhibitor of calmodulin-independent phosphodiesterase, causes 13adrenoceptor subsensitivity in rat cerebral cortex. NaunynSchmiedeberg's Arch Pharmaco1333: 23-30 7. Krause W, Ktihne G (1988) Pharmacokinetics of rolipram in the rhesus and cynomolgus monkeys, the rat and the rabbit. Studies on species differences. Xenobiotica 18:561-571 8. Pfeffer M, Sauerbrey N, Windt-Hanke F, Krause W.In-vitro- and - in a human pharmacokinetic study - in-vivo characterisation of two retard formulations for the antidepressant rolipram. Arzneimittelforschung (in press) 9. Krause W, Kfihne G, Matthes H (1989) Pharmacokinetics of the antidepressant rolipram in healthy volunteers. Xenobiotica, 19: 683~92 10. Drayer DE (1986) Pharmacodynamic and pharmacokinetic differences between drug enantiomers in humans: an overview. Clin Pharmacol Ther 40:125-131 11. Hubbard JW, Ganes D, Lim HK, Midha KK (1986) Clinical pharmacology and its consequences for therapeutic monitoring. Clin Biochem 19:10%112 12. Ariens EJ (1984) Stereochemistry, a basis for sophisticated nonsense in pharmacokinetics and clinical pharmacology. Eur J Clin Pharmaco126:663-668 13. Simonyi M (1984) On chiral drug action. Med Res Rev 4:359-413 14. Brittain RT, Drew GM, Levy GP (1982) The a- and 13-adrenoceptor blocking potencies of labetalol and its individual stereoisomers in anaesthetized dogs and in isolated tissues. Br J Pharmaco177:105-114 15. Elliott HL, Meredith PA, Sumner D J, Reid JL (1984) Comparison of the clinical pharmacokinetics and concentration-effect relationship for medroxalol and labetalol. Br J Clin Pharmaco117: 573-578 16. Cheng HC, Rearis jr OK, Grisar JM, Claxton GP, Weiner DL, Woodward JK (1980) Antihypertensive and adrenergic receptor blocking properties of the enantiomers of medroxalol. Life Sci 27:2529-2534 17. B laschke G, Kraft HR Fickenscher K, Kohler F (1979) Chromatographische Racemattrennung von Thalidomid und teratogene Wirkung der Enantiomere. Arzneimittelforschung 29:1640-1642 18. Olanoff LS, Walle T, Walle UK, Cowart TD, Gaffney TE (1984) Stereoselective clearance and disposition of intravenous propranolol. Clin Pharmacol Ther 35:755-761 19. Walle T, Walle UK, Wilson MJ, Fagan TC, Gaffney TE (1984) Stereoselective ring oxidation of propranolol in man. Br J Clin Pharmaco118: 741-747 20. Bowman WC, Rand MJ (1980) Textbook of Pharmacology, 2nd ed. Blackwell, Oxford 21. Eichelbaum M, Mikus G, Vogelsang B (1984) Pharmacokinetics of ( + ), ( - ), and ( _+)-verapamil after intravenous administration. Br J Clin Pharmaco117: 453-458 22. Ho JK, Harris RA (1981) Mechanism of action of barbiturates. Ann Rev Pharmacol Toxico121: 83-111 23. McGraw NR Callery PS, Castagnoli N jr (1977) In vitro stereoselective metabolism of psychotromimetic amine 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane. An apparent enantiomeric interaction. J Med Chem 20:185-189 24. Ariens E J, Mohr K (1985) Stereochemische Irrwege in der Pharmakotherapie. Dtsch Med Wochenschr 110:1741-1749 Received: March 9, 1989 Accepted in revised form: August 8, 1989 Dr. W. Krause Schering AG Pharmakokinetik B Postfach 65 0311, D-1000 Berlin 65
P[bQQc@e® @ Spfinger-Verlag 1990
Pharmacokinetics of ( + )-rolipram and ( - )-rolipram in healthy volunteers W. K r a u s e , G. Ktthne, a n d N. S a u e r b r e y Research Laboratories of Schering AG, Berlin, Federal Republic of Germany
Summary. Plasma levels of S-( + )-rolipram and R-( - )rolipram in six healthy male volunteers were m e a s u r e d by r a d i o i m m u n o a s s a y after intravenous injection of 0.1 m g and oral administration of 1.0 m g of the pure enantionmers. Following i.v. treatment, plasma levels of b o t h isomers declined in three phases, with half-lives of 0.2 h, 0.64).9 h and 6-8 h. Total clearance was 6 ml. min -~-kg -~. Oral administration of 1.0 m g gave a p e a k c o n c e n t r a t i o n of 16 ng- m l - 1 after 0.5 h. Bioavailability of ( + )-rolipram was 77% and of the ( - ) e n a n t i o m e r it was 74%. T h e r e was no significant difference in Cmax, halflife, total clearance or bioavaflability b e t w e e n the two enantiomers. Key words: Rolipram; enantiomers, pharmacokinetics, healthy volunteers
R o l i p r a m ( I U P A C name: 4-(3-cyclopentyloxy-4-methoxy-phenyl)-2-pyrrolidone) is a selective c A M P phosphodiesterase inhibitor [1, 2], which has been shown to be effective in the t r e a t m e n t of e n d o g e n o u s depression [3, L a e m m e l and Sastre, 1983 unpublished data, 4]. D o p a m i n e r g i c and serotoninergic effects were not o b s e r v e d [5]. The drug was well tolerated without affecting heart rate, b l o o d pressure or o t h e r vital functions. R o l i p r a m is used as the racemate. However, in animal p h a r m a c o l o g y it has b e e n d e m o n s t r a t e d that only the R( - ) - e n a n t i o m e r is the carrier of phosphodiesterase inhibiting activity, and that the S-( + )-isomer is practically devoid o f this p r o p e r t y [6]. T h e r a c e m a t e was administered in previous p h a r m a cokinetic studies in animals and in m a n [7-9], as was the case in all the clinical investigations. T h e aim of the present study was to c o m p a r e the absorption and disposition of the two e n a n t i o m e r s in healthy male volunteers after separate administration of the two pure rolipram isomers.
Materials and methods
Experimental Design Six healthy male volunteers (age 31 (4) y, range 27-37 y; weight 71 (7) kg, range 59-79 kg; height 185 (9) cm, range t73-198 cm) participated in the study. They gave their written informed consent to it beforehand. All volunteers received 0.1 m g ( + )-rolipram and 0.1 m g ( - )rolipram intravenously and 1.0 mg ( + )-rolipram and 1.0 mg ( - )rolipram orally, according to an open randomized cross-over design, with a 2-week interval between treatments. For intravenous injection, rolipram was dissolved in bidist, water with 20% (by weight) propylene glycol at the concentration of 0.1mg.m1-1. For oral use, microcrystalline suspensions in Myrj/physiological saline (0.1 mg/ml) were prepared. All rolipram administrations were performed in the morning, after an overnight fast. Alcohol and caffeine were not allowed. Two weeks before and during the study any comedication was strictly excluded. Blood was collected from an arm vein contralateral to that used for the i.v. injection immediately before the administration of rotipram and 5, 10, 15, 20, 30, 45, 60 and 90 min, and 2, 3, 4, 5, 6, 8, 10, 22 and 24 h after i. v. treatment, and 15, 30, 45, 60 and 90 rain and 2, 3, 4, 6, 8, 10, 12 and 24 h after oral dosing. The plasma was immediately frozen at - 18°C until analyzed.
Methods The concentration of (+)- or (-)-rolipram in plasma was determined by radioimmunoassay. Plasma 0.05-0.2ml was extracted with 2.5 ml diethyl ether after adding saline to give a final sample volume of 0.5 ml. The ether phase was taken to dryness and the residue was redissolved in i ml aqueous bovine serum albumin solution (0.1%, w/v). After incubation with tracer and antiserum (dilution 1:250000) for 16 h at room temperature, bound and unbound fractions were separated with a charcoal suspension containing 5% dextran. After centrifugation, radioactivity was measured in the solution. Calibration was done by constructing a standard curve parallel to the unknown samples. Intra- and inter-assay variability was below 3% and 7%, respectively. The detection limit was 0.1 ng/ml. Because the antiserum had been obtained by immunization of rabbits with
72
W. Krause et al.: Rolipram kinetics
Concentration (ng/ml) 7r-
2~
Fig. 1. Plasma levels (mean and SD) of ( + )-rolipram ( x ) and ( - )-rolipram ( • ) in six healthy male volunteers after i.v. injection of 0.1 mg pure enantiomer
i
I Or o
I
I
h
0.5
1
1.5
2
2.5
3
Time
(h)
3.5
4
4.15
5.5
5
racemic rolipram-3-carboxylic acid coupled to bovine serum albumin, it did not discriminate between the two rolipram enantiomers.
Calculations Pharmacokinetic parameters (half-life, area under the plasma level-time curve (AUC), clearance, and volume of distribution) were calculated by the computer program TOPFIT, using a threecompartment body model. Bioavailability was evaluated by comparing AUC data after p.o. and i.v. administration and correcting for dose. Statistical differences were evaluated by Student's t test for paired data.
or 8.4 h ( - ), respectively. T h e m e a n transit time of ( + )or ( - )-rolipram was 2.7 h and 1.5 h, respectively. F r o m the area under the p l a s m a level-time curve ( A U C ) of 4.2 ( + ) or 4.3 h . n g - m 1 - 1 ( - ) , the total clearance of 6.5 ( + ) or 6.1 ml. m i n - 1. kg 1 ( _ ) was calculated. M e a n p l a s m a levels of the two e n a n t i o m e r s are illustrated in Fig. 1. T h e p h a r m a c o k i n e t i c p a r a m e t e r s of the ( + ) - and ( - ) - e n a n t i o m e r s of r o l i p r a m did not differ significantly except for the initial drug concentration after injection (P < 0.01; Figs.2, 3).
Plasma levels after p. o. administration
Results Plasma levels after i. v. injection A f t e r intravenous injection of ( + )- or ( - )-rolipram, the p l a s m a concentration of the drug declined in three phases (Table 1), with half-lives of 0.16 h (Phase I, both enantiomers), 0.6 h ( + ) or 0.9 h ( - ), and 5.7 h ( + )
B o t h e n a n t i o m e r s of rolipram were rapidly absorbed, achieving p e a k concentrations in p l a s m a of 16 ng/ml after 0.4 ( + ) or 0.5 h ( - ). Thereafter, plasma levels declined in three phases, with half-lives of 0.1 h (Phase I, ( + ) and ( - )), 0.4 h ( + ) or 0.5 h ( - ) (Phase II) and 4.6 h ( + ) or 9.4 h ( - ) (Phase III). M e a n transit time was 3.2 h ( + ) or 4.1h(-).
Table 1. Comparison of mean ( + SD) pharmacokinetic parameters of ( + )- and ( - )-rolipram in 6 healthy male volunteers after i. v. injection of 0.1 mg and p. o. administration of 1.0 mg pure enantiomer i. v. Admin. ( + )-Rolipram Cmax(ng/ml)
3.9
tmax ( h )
-
ha(abs-) (h) tl/2(I)(h) tla(II)(h) tl~ (III) (h) AUC(h.ng-m1-1) AUC(I)(%) AUC(II)(%) AUC(III) (%) V,~(1-kg-:) MTT (h) CL (ml. min - ~.kg- i) Bioavail. (%)
0.16 0.60 5.7 4.24 10.7 57.4 32.0 0.82 2.7 6.5 100
(1.0)
( - )-Rolipram 5.6
(1.2)
-
(0.09) (0.20) (4.0) (2.02) (12.4) (19.7) (23.6) (0.51) (2.9) (2.5) (0)
0.16 0.92 8.4 4.27 21.4 74.8 3.9 0.52 1.5 6.1 100
(0.08) (0.30) (0.2) (1.46) (13.2) (10.1) (5.3) (0.18) (0.5) (2.2) (0)
p.o. Admin. ( + )-Rolipram
( - )-Rolipram
15.7
(5.2)
16.4
(5.1)
0.4
(0.1)
0.5
(0.3)
0.25 0.13 0.62 4.6 29.2 12.1 53.9 33.9 3.2 77
(0.29) (0.12) (0.21) (3.2) (7.81) (11.0) (15.7) (8.7)
0.22 0.13 0.87 9.4 28.9 19.5 57.9 22.6 4.1 74
(0.23) (0.19) (0.51) (7.8) (7.92) (16.9) (18.2) (5.4)
(2.2) (32)
(2.9) (31)
73
W. Krause et al.: Rolipram kinetics Clearance (ml/min/kg) 10,
Fig.2. Total clearance of ( + )-rolipram ( 1 ) and
( - )-rolipram ( [ ] ) in six healthy male volunteers after i. v. injection of 0.1 mg pure entantiomer 1
2
3
4
5
6
Subject No.
1,6 r
a''l
o,8
n
0,6 T
0,4
0,2 0
1
2
3
4
5
6
I
lO
b "~
8
¢
6
,c
4
7-
Fig.3. Half-lives of disposition Phases II (top) and IfI (bottom) of ( + )-rolipram and ( - )-rolipram in six healthy male volunteers after i.v. injection of 0.1 mg pure enantiomer. Key as in Fig. 1
2
T
o
1
2
4
3
Subject
5
6
No.
Concentration (ng/ml) 25 I
20
15
10
0
.
0
2
4
.
.
.
6
Time (h)
•
8
10
Fig.4. Plasma levels (mean and SD) of ( + )-rolipram ( x ) and ( - )-rolipram ( • ) in six healthy male volunteers after p. o. administration of 1.0 mg pure enantiomer
"
12
14
74
W. Krause et al.: Rolipram kinetics
30,
Cmax (ng/ml)
25 20
15 10
Fig.5. Peak plasma level of ( + )-rolipram and ( - )-rolipram in six healthy male volunteers after p. o. administration of 1.0 mg pure enantiomer. Key as in Fig. 1
5 0
1
3
2
4
Subject No. Bioavailability (%) 160~
I
14o I 120 100
80 60
Fig.6. Bioavailability of ( + )-rolipram and ( - )-rolipram in six healthy male volunteers after p. o. administration of 1.0 mg pure enantiomer. Key as in Fig. 1
40 20 0 1
2
3
4
5
S u b j e c t No. From an A U C of 29 h-ng. ml 1, bioavailability was calculated as 77% ( + ) or 74% ( - ). Mean plasma levels are illustrated in Fig.4. Except for the partial area of disposition Phase III (0.01 < P < 0.05), the pharmacokinetic parameters of ( + )- and ( - )-rolipram were not significantly different (Figs. 5, 6). Discussion The aim of the present study was to investigate whether there were any differences in the absorption and disposition of the two enantiomers of rolipram. Only the ( - )form possesses antidepressant activity. Six healthy male volunteers were treated separately with each of the two isomers intravenously in the dose of 0.1 rag, and orally with 1.0 mg. The study followed an open randomized four-way cross-over design. Plasma levels of rolipram were determined by radioimmunoassay with an antiserum which had been raised against the racemate and therefore did not differentiate between the two enantiomers. Except for the starting concentration after i.v. injection, and for the partial area of disposition Phase III after p.o. treatment, statistical evaluation did not reveal any significant difference in the pharmacokinetic parameters of the two forms of rolipram. Neither difference is relevant to the estimation of the safety or efficacy of rolipram. Starting concentrations after i.v. injection strongly depend on the exact timing of
the duration of injections and on identical (within seconds) timing of the first sampling point. Terminal partial areas are strongly influenced by the sensitivity and reproducibility of the analytical method used. In the present study radioimmunoassay was employed and plasma levels were followed until the limit of detection was reached. Near that limit, data are necessarily subject to decreased precision and accuracy, which will strongly influence the last part of the terminal phase. The bioavailability of rolipram was 50-80% in five volunteers, and one other subject had values of 130 to 140% for both enantiomers. A possible reason for the discrepancy is non-linearity of rolipram kinetics, but that was only apparent in the one volunteer, or a decreased metabolizing capacity for rolipram, due either to hepatic insufficiency or to a difference in the metabolic phenotype (poor/extensive metabolizers). Hepatic insufficiency can be excluded, because all the volunteers were extensively checked, including liver funtion tests, prior to and after the study. Whether the metabolic phenotype (oxidizing capacity) is of importance in the pharmacokinetic handling of rolipram is not known. As a result of the present investigation, the pharmacokinetics of rolipram can adequately be described by the kinetic parameters of the racemate after correction for dose. It will not be necessary to measure separate plasma levels of the pharmacologically active ( - )-enantiomer in future studies.
75
w. Krause et al.: Rolipram kinetics Chiral p h a r m a c o l o g y and pharmacokinetics have gained considerably in i m p o r t a n c e in recent years [10-13]. T h e r e are three principal aspects of chirality in p h a r m a cotherapy. • Enantioselective drug action • Enantioselective p h a r m a c o k i n e t i c s / b i o t r a n s f o r m a t i o n • Interaction of e n a n t i o m e r s - at the r e c e p t o r level - kinetic/metabolic interaction Enantioselective drug action requires that the center of chirality in the molecule interacts with the receptor, causing differential efficacy of the two enantiomers. Examples of this type of drug are rolipram, ~3-blockers, such as labetalol [14, 15] and m e d r o x a l o l [16], and thalidomide which exerts a teratogenic action exclusively t h r o u g h the ( - )enantiomer, as the ( + ) - a n t i p o d e is inactive [17]. E n a n tioselective p h a r m a c o k i n e t i c s and/or biotransformation have b e e n r e p o r t e d for p r o p a n o l o l [18, 19], m e t h a c h o l i n [20] and verapamil [21]. T h e interaction of e n a n t i o m e r s has b e e n o b s e r v e d for barbiturates, where ( + ) isomers m a y cause central n e r v o u s system excitation, and the ( - )isomers are sedative [22], and for s o m e p s y c h o m i m e t i c amines, w h e r e the presence of one e n a n t i o m e r effectively inhibited the m e t a b o l i s m of the other [23]. T h e use of racemic drugs in t h e r a p y has b e e n questioned for all these reasons [12, 24]. However, as long as there is no selective side-effect of the pharmacologically "inactive" antipode, no interaction of the two enantiomers, and w h e n e v e r the p h a r m a c o k i n e t i c s of the "active" isomer can easily be determined, for example by stereoselective analysis, there should be no obj ection to the introduction of racemic mixtures. In the case of rolipram, due to the identical p h a r m a c o k i n e t i c b e h a v i o u r of the two antipodes, not even stereoselective analysis should be necessary. Interaction at the kinetic/metabolic level appears unlikely, because the chiral center is not attacked during biot r a n s f o r m a t i o n [Krause and Kfihne, 1987, unpublished data], and, in addition, the clearance rates of the enantiomers are identical w h e n t h e y are given separately. T h e p h a r m a c o k i n e t i c s of the active isomer of rolipram, therefore, can adequately be described by the parameters of the r a c e m a t e after correction for dose.
Acknowledgement. Synthesis of the ( + )- and ( - ) isomers of rolipram by Dr. R. Schmiechen is gratefully acknowledged.
References 1. Wachtel H (1982) Characteristic behavioural alteration in rats induced by rolipram and other selective adenosine cyclic 3', 5'monophosphate phosphodiesterase inhibitors. Psychopharmacotogy 77:30%316 2. Wachtel H (1983) Potential antidepressant activity of rolipram and other selective cyclic adenosine 3', 5'-monophosphate phosphodiesterase inhibitors. Neuropsychopharmacology 22: 267272 3. Horowski R, Sastre M (1985) Clinical effects of the neurotropic selective cAMP phosphodiesterase inhibitor rolipram in depressed patients: Global evaluation of the preliminary reports. Current Ther Res 38:23-29
4. Zeller E, Stief H J, Pflug B, Sastre-y-Hernandez M (1984) Results of a phase II study of the antidepressant effect of rolipram. Pharmacopsychiatry 17:188-190 5. Przegalinski E, Bigajska K, Lewandowska A (1981) The influence of rolipram in the central serotoninergic system. Pharmacopsychiatry 14:162-166 6. Schultz JE, Schmidt B H (1986) Rolipram, a stereospecific inhibitor of calmodulin-independent phosphodiesterase, causes 13adrenoceptor subsensitivity in rat cerebral cortex. NaunynSchmiedeberg's Arch Pharmaco1333: 23-30 7. Krause W, Ktihne G (1988) Pharmacokinetics of rolipram in the rhesus and cynomolgus monkeys, the rat and the rabbit. Studies on species differences. Xenobiotica 18:561-571 8. Pfeffer M, Sauerbrey N, Windt-Hanke F, Krause W.In-vitro- and - in a human pharmacokinetic study - in-vivo characterisation of two retard formulations for the antidepressant rolipram. Arzneimittelforschung (in press) 9. Krause W, Kfihne G, Matthes H (1989) Pharmacokinetics of the antidepressant rolipram in healthy volunteers. Xenobiotica, 19: 683~92 10. Drayer DE (1986) Pharmacodynamic and pharmacokinetic differences between drug enantiomers in humans: an overview. Clin Pharmacol Ther 40:125-131 11. Hubbard JW, Ganes D, Lim HK, Midha KK (1986) Clinical pharmacology and its consequences for therapeutic monitoring. Clin Biochem 19:10%112 12. Ariens EJ (1984) Stereochemistry, a basis for sophisticated nonsense in pharmacokinetics and clinical pharmacology. Eur J Clin Pharmaco126:663-668 13. Simonyi M (1984) On chiral drug action. Med Res Rev 4:359-413 14. Brittain RT, Drew GM, Levy GP (1982) The a- and 13-adrenoceptor blocking potencies of labetalol and its individual stereoisomers in anaesthetized dogs and in isolated tissues. Br J Pharmaco177:105-114 15. Elliott HL, Meredith PA, Sumner D J, Reid JL (1984) Comparison of the clinical pharmacokinetics and concentration-effect relationship for medroxalol and labetalol. Br J Clin Pharmaco117: 573-578 16. Cheng HC, Rearis jr OK, Grisar JM, Claxton GP, Weiner DL, Woodward JK (1980) Antihypertensive and adrenergic receptor blocking properties of the enantiomers of medroxalol. Life Sci 27:2529-2534 17. B laschke G, Kraft HR Fickenscher K, Kohler F (1979) Chromatographische Racemattrennung von Thalidomid und teratogene Wirkung der Enantiomere. Arzneimittelforschung 29:1640-1642 18. Olanoff LS, Walle T, Walle UK, Cowart TD, Gaffney TE (1984) Stereoselective clearance and disposition of intravenous propranolol. Clin Pharmacol Ther 35:755-761 19. Walle T, Walle UK, Wilson MJ, Fagan TC, Gaffney TE (1984) Stereoselective ring oxidation of propranolol in man. Br J Clin Pharmaco118: 741-747 20. Bowman WC, Rand MJ (1980) Textbook of Pharmacology, 2nd ed. Blackwell, Oxford 21. Eichelbaum M, Mikus G, Vogelsang B (1984) Pharmacokinetics of ( + ), ( - ), and ( _+)-verapamil after intravenous administration. Br J Clin Pharmaco117: 453-458 22. Ho JK, Harris RA (1981) Mechanism of action of barbiturates. Ann Rev Pharmacol Toxico121: 83-111 23. McGraw NR Callery PS, Castagnoli N jr (1977) In vitro stereoselective metabolism of psychotromimetic amine 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane. An apparent enantiomeric interaction. J Med Chem 20:185-189 24. Ariens E J, Mohr K (1985) Stereochemische Irrwege in der Pharmakotherapie. Dtsch Med Wochenschr 110:1741-1749 Received: March 9, 1989 Accepted in revised form: August 8, 1989 Dr. W. Krause Schering AG Pharmakokinetik B Postfach 65 0311, D-1000 Berlin 65
