USE OF DRUGS WITH MORE THAN A TWENTY-4-HOUR DURATION OF ACTION

Aim: To assess compliance with a drug regimen of two doses a day compa red with one a day. Patients and methods: A prospective crossover stud y was set up in a general practice environment to compare compliance o n a drug regimen of once a day versus twice a day. Data were collected by electronic monitoring in 113 patients with hypertension or angina pectoris. All patients were prescribed slow-release nifedipine twice a day during the first month and then crossed to a single daily dose of amlodipine for another month. Results: Compliance, defined as the pro portion of days on which the correct dose was taken, improved in 30% o f patients (95% confidence interval 19-41%; P<0.001) when the patients were switched from twice a day to once a day, but at the same time th ere was a 15% increase (95% confidence interval 5-25%; P<0.02) in the number of patients with one or more no-dose days. Approximately 8% of patients displayed low compliance, irrespective of the dose regimen. A ctual dose intervals were used to estimate the extent and timing of pe riods with unsatisfactory drug activity for various hypothetical drug durations of action. Conclusions: The apparent advantage of a single d aily dose in terms of compliance appears to be clinically meaningful o nly when the duration of activity extends beyond the dose interval in all patients.