Effect of cytochrome P450 inhibitors (diethyl dithiocarbamate, ketoconazole and grapefruit juice) on the pharmacokinetics of all-trans-retinoic acid.

Diethyl dithiocarbamate (DEDTC) has been reported to be a more powerful inhibitor of all-trans-retinoic acid (ATRA) in vitro metabolism than the well-established cytochrome P450 (CYP) inhibitor ketoconazole (KC). In recent years grapefruit juice (GJ) has been shown to be able to increase the oral bioavailability of several drugs by inhibiting intestinal CYP. This study investigated the in vivo effect of these CYP inhibitors on the pharmacokinetics of ATRA. The latter was administered to rats as a constant-rate intravenous (i.v.) infusion (0.48 mg h(-1) kg(-1)) during 10 h and orally (1.6 mg kg(-1)). DEDTC (320 mg kg(-1) x 2 i.v., 6.4 and 32 mg kg(-1) per os (p.o.)) did not change the ATRA c…