Effect of silibinin on the pharmacokinetics of nitrendipine in rabbits

Silibinin, a major constituent of silymarin, is widely used for its hepatoprotective effects. This study investigated the effect of silibinin on the pharmacokinetics of oral nitrendipine in rabbits. In first set of experiment, male New Zealand rabbits were pretreated with silibinin (50 mg/kg, PO) for 7 days and on last day nitrendipine (10 mg/kg, PO) was administered. In second set, both silibinin and nitrendipine were coadministered to examine acute effect of silibinin on nitrendipine pharmacokinetics. The plasma concentration of nitrendipine was estimated by high performance liquid chromatography and different pharmacokinetic parameters were calculated using WinNonlin(®) software. Coadministration of silibinin had no significant effect on pharmacokinetics of nitrendipine when compared to control group. However, a 1.89-1.57-fold increase in area under the concentration-time curve and peak plasma concentration (C max), respectively, of nitrendipine was observed in silibinin pretreated group. The mean C max was 0.034 ± 0.005 μg/mL (nitrendipine alone) and 0.054 ± 0.006 μg/mL (nitrendipine after pretreatment with silibinin). The time to reach C max, elimination rate constant and elimination half-life of nitrendipine were not significantly different among control and silibinin treated groups. This study demonstrates that silibinin increase plasma concentration of nitrendipine. Henceforth, the pharmacodynamic influence of this interaction should be taken into consideration while prescribing nitrendipine to the patients already taking silymarin.