Patient compliance and therapeutic coverage: amlodipine versus nifedipine (slow-release) in the treatment of angina pectoris. Belgian Collaborative Group.

Patient compliance with therapy is often poor and overestimated by the treating physician; it is particularly important in cardiovascular diseases such as hypertension and angina pectoris. Compliance was studied in an open parallel study in out-patients with stable angina pectoris, given either amlodipine (5 mg, once daily) or slow-release nifedipine (20 mg, twice daily) for 12 weeks. Compliance was assessed using pill counting and using an electronic device, the medication event monitoring system, to record the time and date of each opening and closure of the pill container. There was no difference between the two groups in pill count or in 'taking compliance' (the percentage of prescribed doses taken as indicated by the monitoring system). Compliance was significantly better (P < 0.001) with amlodipine, however, for 'correct dosing' (the percentage of days on which the correct dose was taken) and for 'timing compliance' (the percentage of doses taken at the prescribed time interval after the last dose). 'Therapeutic coverage' (the estimated proportion of treatment time for which the drug was active) was also significantly better for amlodipine (P < 0.001). There was no difference in reported side-effects between the two therapies.