Inhibitory effect of stiripentol on carbamazepine and saquinavir metabolism in human.
OBJECTIVE
To characterize the in vitro and in vivo inhibitory effect of stiripentol, a new anticonvulsant, on the metabolism of carbamazepine and saquinavir, which are substrates of CYP3A4.


METHODS
Human liver microsomes and cDNA-expressed CYP enzymes were used for the in vitro experiments. Pharmacokinetic data from epileptic children and healthy adults were used for the carbamazepine and saquinavir in vivo studies, respectively.


RESULTS
Carbamazepine biotransformation to its 10,11-epoxide by human liver microsomes (Vmax = 10.3 nmol min(-1) nmol(-1) P450, apparent Km = 362 microm), cDNA-expressed CYP3A4 (Vmax = 1.17 nmol min(-1) nmol(-1) P450, apparent Km = 119 microm) and CYP2C8 (Vmax = 0.669 nmol min(-1) nmol(-1) P450, apparent Km = 757 microm) was inhibited by stiripentol (IC50 14, 5.1, 37 microM and apparent Ki 3.7, 2.5, 35 microm, respectively). Saquinavir biotransformation to its major metabolite M7 by human liver microsomes (Vmax = 5.7 nmol min(-1) nmol(-1) P450, apparent Km = 0.79 microm) was inhibited by stiripentol (IC50 163 microM, apparent Ki 86 microm). In epileptic children treated with carbamazepine and stiripentol, the plasma concentration ratio of carbamazepine epoxide/carbamazepine was decreased by 65%. The in vivo apparent Ki for stiripentol ranged from 10.5 to 41.4 microm. The pharmacokinetics of saquinavir was not modified by stiripentol in healthy adults. The 95% confidence intervals for the difference for Cmax and AUC of saquinavir between the placebo and stiripentol phase were (-39.8, 39.8) and (-33.2, 112), respectively.


CONCLUSIONS
These results showed that stiripentol was a weak inhibitor of saquinavir metabolism both in vitro and in vivo. In contrast, stiripentol is a potent inhibitor of carbamazepine 10,11-epoxide formation in vitro and in vivo in epileptic patients.
Cazali
N
N
Pharmacologie, Université René Descartes, Hôpital Saint-Vincent de Paul, Assistance Publique-Hôpitaux de Paris, Paris, France.
Tran
A
A
Treluyer
J M
JM
Rey
E
E
d'Athis
P
P
Vincent
J
J
Pons
G
G
D000293:Adolescent; D000927:Anticonvulsants / Q000494:pharmacology*; D002220:Carbamazepine / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors*; D002648:Child; D002851:Chromatography, High Pressure Liquid; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004148:Dioxolanes / Q000494:pharmacology*; D004347:Drug Interactions; D017320:HIV Protease Inhibitors / Q000037:antagonists & inhibitors*; D006801:Humans; D066298:In Vitro Techniques; D008862:Microsomes, Liver / Q000378:metabolism; D019258:Saquinavir / Q000037:antagonists & inhibitors*; D013997:Time Factors
D000927:Anticonvulsants; D004148:Dioxolanes; D017320:HIV Protease Inhibitors; D002220:Carbamazepine; D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D019258:Saquinavir; C012227:carbamazepine epoxide; C021092:stiripentol