The efficacy and safety profile of simvastatin and pravastatin across their most commonly recommended dosage ranges were compared in a double-blind, parallel, multicenter study in 550 patients with primary hypercholesterolemia. The study consisted of a 6-week placebo period followed by 18 weeks of active treatment. Patients were randomized to 10 mg of simvastatin or pravastatin once in the evening; doses were titrated at 6-week intervals to a maximum of 40 mg/day if the low-density lipoprotein (LDL) cholesterol remained > or = 130 mg/dl (3.4 mmol/liter). Baseline characteristics were similar in both groups. At the end of the study with simvastatin and pravastatin, respectively, 30 and 14% continued to take the 10 mg dose and 48 and 66% were titrated to the maximal dose. After 18 weeks of treatment with simvastatin and pravastatin the mean percent decreases from baseline were, respectively, for total plasma cholesterol 27 and 19% (p < 0.01 between groups), for LDL cholesterol 38 and 26% (p < 0.01 between groups), for very low density lipoprotein cholesterol 30 and 16% (p < 0.01 between groups), and for triglycerides 18 and 14% (p < 0.05 between groups). The mean percent increase from baseline in high-density lipoprotein cholesterol was 15% with simvastatin compared to 12% with pravastatin (p < 0.05 between groups). The efficacy goal of LDL cholesterol < 130 mg/dl was achieved in 65% of the patients treated with simvastatin versus 39% of those treated with pravastatin (p < 0.001). There was no significant difference between groups in the frequency of drug-related adverse experiences.(ABSTRACT TRUNCATED AT 250 WORDS)