[Unexpected interactions of some psychotropic drugs with barbital and pentobarbital effects in mice (author's transl)].

Some of the substances studied modified the effects of the two barbiturates as expected and in the same direction: --chlorpromazine and diazepam increased the effects; --amphetamine and caffeine decreased them. Barbital, unlike pentobarbital, undergoes almost no metabolic transformation. This explains why pentobarbital is potentiated in the presence of proadifen, an inhibitor of liver microsomial enzymes, whereas the effect of barbital is unchanged, and probably explains similar results obtained with iproniazide and imipramine. For the same reason, rifampicine, an enzyme inducer, antagonizes the effect of pentobarbital without affecting that of barbital. The dissociated effects obtained with other substances are more difficult to explain: --increased effects of barbital without modification of the effects of pentobarbital (sulpiride); --decreased effects of barbital without modification of the effects of pentobarbital (methylphenidate, nomifensine, amineptine, oxolinic acid, methysergide); --decreased effects of barbital with increased effects of pentobarbital (viloxazine). Two hypotheses may be considered: 1. The study of barbital and pentobarbital concentrations in blood and brain would allow to exclude a pharmacokinetic interaction; 2. Barbital does not act through the same mechanism as pentobarbital.