Influence of stiripentol on cytochrome P450-mediated metabolic pathways in humans: in vitro and in vivo comparison and calculation of in vivo inhibition constants.
OBJECTIVE
The spectrum of cytochrome P450 inhibition of stiripentol, a new anticonvulsant, was characterized in vitro and in vivo.


METHODS
Stiripentol was incubated in vitro with (R)-warfarin, coumarin, (S)-warfarin, (S)-mephenytoin, bufuralol, p-nitrophenol, and carbamazepine as probes for CYPs 1A2, 2A6, 2C9, 2C19, 2D6, 2E1, and 3A4, respectively. Caffeine demethylation and the 6 beta-hydroxycortisol/cortisol ratio were monitored in vivo before and after 14 days of treatment with stiripentol as measures of CYP1A2 and CYP3A4 activity, and dextromethorphan O- and N-demethylation were used to measure CYP2D6 and CYP3A4 activity, respectively. In vivo inhibition constants for CYP3A4 were calculated with use of data that previously documented the interaction between stripentol and carbamazepine.


RESULTS
In vitro, stiripentol inhibited CYPs 1A2, 2C9, 2C19, 2D6, and 3A4, with inhibition constant values at or slightly higher than therapeutic (total) concentrations of stiripentol, but it did not inhibit CYPs 2A6 and 2E1 even at tenfold therapeutic concentrations. In vivo inhibition of caffeine demethylation and dextromethorphan N-demethylation were consistent with inhibition of CYP1A2 and CYP3A4, respectively. The 6 beta-hydroxycortisol/cortisol ratio did not provide a reliable index of CYP3A4 inhibition. Inhibition of CYP2D6-mediated O-demethylation was not observed in vivo. With use of carbamazepine, in vivo inhibition constants for CYP3A4 ranged between 12 and 35 mumol/L, whereas the corresponding in vitro value was 80 mumol/L.


CONCLUSIONS
Stiripentol appears to inhibit several CYP450 enzymes in vitro and in vivo. In vivo inhibition constants show that stiripentol inhibition of CYP3A4 is linearly related to plasma concentration in patients with epilepsy.
Tran
A
A
Département de Pharmacologie Périnatale et Pédiatrique, Hôpital Saint Vincent de Paul-Université René Descartes Paris V.
Rey
E
E
Pons
G
G
Rousseau
M
M
d'Athis
P
P
Olive
G
G
Mather
G G
GG
Bishop
F E
FE
Wurden
C J
CJ
Labroo
R
R
Trager
W F
WF
Kunze
K L
KL
Thummel
K E
KE
Vincent
J C
JC
Gillardin
J M
JM
Lepage
F
F
Levy
R H
RH
D000328:Adult; D000927:Anticonvulsants / Q000737:chemistry / Q000494:pharmacology*; D002110:Caffeine; D002245:Carbon Dioxide / Q000032:analysis; D002247:Carbon Isotopes; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003915:Dextromethorphan; D004148:Dioxolanes / Q000737:chemistry / Q000494:pharmacology*; D004827:Epilepsy / Q000188:drug therapy / Q000201:enzymology; D006801:Humans; D006854:Hydrocortisone; D066298:In Vitro Techniques; D006899:Mixed Function Oxygenases / Q000037:antagonists & inhibitors; D012016:Reference Values; D013997:Time Factors
D000927:Anticonvulsants; D002247:Carbon Isotopes; D065607:Cytochrome P-450 Enzyme Inhibitors; D004148:Dioxolanes; D002245:Carbon Dioxide; D002110:Caffeine; D003915:Dextromethorphan; D006899:Mixed Function Oxygenases; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; C021092:stiripentol; D006854:Hydrocortisone