The effect of medication compliance on the control of hypertension.

The effect of medication-taking patterns on blood pressure was investigated in 24 hypertensive outpatients being treated with once-daily doses of hydrochlorothiazide or chlorthalidone. Medication-taking patterns were measured with a small pill dispenser that electronically records the time of medication removal. Blood pressure reduction was found to correlate better with the total number of doses the patient removed from the pill pack during a month than with any of four other compliance measures that were based on the timing of dose removal. Analysis also suggested that blood pressure is improved if patients ingest omitted doses to "catch up" to the prescribed regimen. It is concluded that a simple pill count may be the most clinically relevant definition of compliance for patients with hypertension being treated with only hydrochlorothiazide or chlorthalidone, and that such patients should ingest all prescribed doses, regardless of the time interval between doses.