Pharmacokinetic and pharmacodynamic interactions between simvastatin and diltiazem in patients with hypercholesterolemia and hypertension

Pharmacokinetic and pharmacodynamic interactions between simvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, and diltiazem, a calcium antagonist, were investigated in 7 male and 4 female patients with hypercholesterolemia and hypertension. The patients were given, for one in a three consecutive 4-week periods, oral simvastatin (5 mg/day), oral simvastatin (5 mg/day) combined with diltiazem (90 mg/day), and then oral diltiazem (90 mg/day), respectively. The area under the plasma concentration versus time curve up to 6 hours post-dose (AUC0-6h) and maximum plasma concentrations (Cmax) of the drugs, serum lipid profiles, blood pressures and liver functions were assessed on the last day of each of the three 4-week periods. After the combined treatment period, Cmax of HMG-CoA reductase inhibitor was elevated from 7.8 +/- 2.6 ng/ml to 15.4 +/- 7.9 ng/ml (P < 0.01) and AUC0-6h from 21.7 +/- 4.9 ng x hr/ml to 43.3 +/- 23.4 ng x hr/ml (P < 0.01), while Cmax of diltiazem was decreased from 74.2 +/- 36.4 ng/ml to 58.6 +/- 18.9 ng/ml (P < 0.05) and its AUC0-6h from 365 +/- 153 ng x hr/ml to 287 +/- 113 ng x hr/ml (P < 0.01). Compared to simvastatin monotherapy, combined treatment further reduced LDL-cholesterol levels by 9%, from 129 +/- 16 mg/dl to 119 +/- 17 mg/dl (P < 0.05). No adverse events were observed throughout the study. These apparent pharmacokinetic interactions, namely the increase of HMG-CoA reductase inhibitor concentration by diltiazem and the decrease of diltiazem concentration by simvastatin, enhance the cholesterol-lowering effects of simvastatin during combined treatment.