Simvastatin and pravastatin, two 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors, were compared in a multinational, randomized, double-blind trial. Patients demonstrating moderate hypercholesterolemia after 10 weeks on a lipid-lowering diet received 6 weeks of treatment with 5 mg/day simvastatin (n = 143) or 10 mg/day pravastatin (n = 138); the simvastatin dose was increased to 10 mg for an additional 6 weeks while the pravastatin dose remained at 10 mg. When administered at lower or equivalent daily doses, simvastatin was significantly more effective than pravastatin in reducing total and low-density lipoprotein (LDL) cholesterol. Reductions in plasma total and LDL cholesterol were significantly greater with 5 mg simvastatin (16 and 23%) compared to 10 mg pravastatin (12 and 18%; p < or = 0.01). The efficacy of 10 mg simvastatin in lowering these lipid parameters was also superior (19 vs. 11% and 27 vs. 17%, respectively; p < or = 0.01). At 6 and 12 weeks, a significantly higher percentage of simvastatin patients (45 and 59%, respectively) achieved a desirable LDL cholesterol level of < 130 mg/dl (< 3.4 mmol/l) compared to pravastatin patients (32-33%; p < or = 0.05). Both drugs were well tolerated and had comparable safety profiles.