LAUSR

Aims: The first‐line anti‐epileptic agent carbamazepine has narrow therapeutic index and can potentially interact with piperine, the major component from black pepper. The present study aimed to delineate the mechanism of such interaction for safe usage of carbamazepine during epilepsy control. Materials and methods: The effect of piperine on carbamazepine hepatic metabolism was examined using rat or human liver microsomes. Mechanistic static model was applied to predict the extent of interaction. In addition, liver microsomal activities, mRNAs and protein expressions of genes regulating carbamazepine metabolism were evaluated after two weeks oral administrations of 3.5 and 35 mg/kg piperine in rats. Moreover, the effect of piperine on the xenobiotic receptor constitutive androstane receptor (CAR) was further accessed. Key findings: Time‐dependent inhibitory effect of piperine on carbamazepine metabolism was observed, with kinact and KI of 0.0153 min−1 and 18.34 &mgr;M for rat, and 0.0093 min−1 and 9.45 &mgr;M for human. Based on such in‐vitro metabolic parameters, further estimation using mechanistic static model indicated that piperine could increase the AUC of CBZ by 7% and 11% in rat and human, respectively. Significant inhibition on rat liver microsomal activity, Cyp3a2 mRNA and protein expression, CAR mRNA were demonstrated with piperine at 35 mg/kg. Yet, no direct effect on the activity of CAR for piperine was found. Significance: We have demonstrated the time‐dependent inhibition by piperine on carbamazepine metabolism as the interaction mechanism. Prolonged use of piperine at high dose could increase carbamazepine concentrations through inhibiting metabolic enzyme activities and their related genes expressions.