The use of self-measured blood pressure determinations in assessing dynamics of drug compliance in a study with amlodipine once a day, morning versus evening

OBJECTIVE: To test whether the time of administration influences the therapeutic response to a calcium antagonist taken once a day. Also, the dynamics of drug compliance and its impact on blood pressure control were investigated. DESIGN: Twenty outpatients with mild-to-moderate hypertension were included in a randomized, placebo-controlled open study. In a crossover design, all of the patients received 5 mg amlodipine, either in the morning or in the evening, during two consecutive 4-week treatment periods. METHODS: Blood pressure was taken by casual measurement, ambulatory 24-h monitoring (SpaceLabs 90202) and self-measurement at home, performed with a semi-automatic oscillometric device during the whole study period. Compliance was assessed using the Medication-Event-Monitoring System (MEMS). RESULTS: Neither casual nor ambulatory day- or night-time readings detected a significant difference between morning and evening administration. However, self-measurement documented significantly greater blood pressure reductions for morning than for evening administration. The MEMS showed different compliance on the days of ambulatory monitoring (100% with both drug regimens) compared with the whole treatment period. The number of days with missed medication was thus significantly higher for the evening dosing regimen. The difference in self-measured blood pressure between the two regimens was lost if the days with missed medication were removed from the statistical analysis. CONCLUSIONS: Time of once-a-day amlodipine administration does not influence its efficacy for 24-h blood pressure control. Furthermore, the use of self-measurement and the MEMS may provide useful additional information on the pharmacodynamic impact of different dosing patterns in hypertensive patients.