AIM: To assess dosing and determinants of the choice of statins among starters of statins. METHODS: Data were obtained from the PHARMO database comprising pharmacy and linked hospital discharge records of approximately 300 000 subjects in the Nethelands. All new users of statins in 1998 were selected. Patient characteristics and drug regimens were compared between starters of different statins. Odds ratios (OR) and 95% confidence intervals (CI) were calculated using polytomous logistic regressionmodelling, using the start of simvastatin therapy as reference category. RESULTS: In 1998, 1738 patients started using simvastatin (41.1%), pravastatin (23.1%), fluvastatin (11.9%), atorvastatin (22.8%) or cerivastatin (1.0%). Compared with starters withsimvastatin [mean dose 1.02 +/- 0.39 defined daily doses (DDDs)], starters with pravastatin (1.27 +/- 0.56 DDDs) and atorvastatin (1.43 +/- 0.59 DDDs) received higher doses (P < 0.001), whereas users of fluvastatin (0.78 +/- 0.37 DDDs) and cerivastatin(0.81 +/- 0.30 DDDs) received lower doses (P < 0.001). Patients already using CYP3A4 inhibitors more frequently received fluvastatin (OR = 1.80; 95% CI 1.11, 2.94), metabolized by non-CYP3A4 pathways, and atorvastatin (OR = 1.62; 95% CI 1.06, 2.47), which is metabolized by CYP3A4, than simvastatin. Statin doses were not adjusted when prescribed to patients using CYP3A4 inhibitors. CONCLUSIONS: Many patients starting statin therapy did not receive a statin of first choice. The coadministration of potentially interacting drugs may have led to a change in statin choice, but not in dosage lowering. These findings suggest that the quality of statin therapy could be improved.