Effects of HMG-CoA reductase inhibitors on the pharmacokinetics of nifedipine in rats: Possible role of P-gp and CYP3A4 inhibition by HMG-CoA reductase inhibitors.

BACKGROUND: This study aimed to investigate the effects of HMG-CoA reductase inhibitors on the pharmacokinetics of nifedipine in rats.

METHODS: We determined the pharmacokinetic parameters of nifedipine and dehydronifedipine in rats after oral and intravenous administration of nifedipine without and with HMG-CoA reductase inhibitors. We evaluated the effect of HMG-CoA reductase inhibitors on the activity of P-glycoprotein (P-gp) and cytochrome P450 (CYP)3A4.

RESULTS: Atorvastatin, fluvastatin, pravastatin and simvastatin inhibited CYP3A4 activities; inhibitory concentration (IC50) values were 47.0, 5.2, 15.0 and 3.3 μM, respectively. Simvastatin and fluvastatin increased the cellular uptake of rhodamine-123. The area under the plasma concentration-time curve (AUC0-∞) and the peak plasma concentration (Cmax) of oral nifedipine were significantly increased by fluvastatin and simvastatin, respectively, compared to control group. The total body clearance (CL/F) of nifedipine after oral administration with fluvastatin and simvastatin were significantly decreased compared to those of control. The metabolite-parent AUC ratio (MR) of nifedipine with fluvastatin and simvastatin were significantly decreased, which suggested that fluvastatin and simvastatin inhibited metabolism of nifedipine, respectively. The AUC0-∞ of intravenouse nifedipine with fluvastatin and simvastatin was significantly higher than that of the control group.

CONCLUSION: The increased bioavailability of nifedipine may be mainly due to inhibition of both P-gp in the small intestine and CYP3A subfamily-mediated metabolism of nifedipine in the small intestine and/or in the liver and to the reduction of the CL/F of nifedipine by fluvastatin and simvastatin.