Background: It has not been fully elucidated whether antihypertensive medication adherence affects blood pressure (BP) control in hypertension cases. Aim: To investigate the association of adherence to antihypertensive drug regimens and BP control using data from the Combination Pill of Losartan Potassium and Hydrochlorothiazide for Improvement of Medication Compliance Trial (COMFORT) study. Design: An observational analysis from a randomized controlled trial. Methods: A total of 203 hypertensive subjects were randomly assigned to a daily regimen of a combination pill (losartan 50 mg/hydrochlorothiazide 12.5 mg) or two pills, an angiotensin II receptor blocker and a thiazide diuretic. Medication adherence calculated based on pill counts and BPs was evaluated at 1, 3 and 6 months after randomization. Results: The subjects were divided into three groups according to their adherence, i.e. relatively low-adherence (<90%; n = 19), moderate-adherence (90-99%; n = 71) and high-adherence (100%; n = 113) groups. Clinical characteristics of the subjects including BP, sex, randomized treatments and past medical history did not differ significantly among the three groups. Achieved follow-up BPs over the 6-month treatment period, which were adjusted for age, sex,baseline BP and randomized treatment, were significantly higher in the lowadherence group (135/78 mmHg) compared with the high-adherence (130/74 mmHg;P = 0.02/0.02) and the moderate-adherence (128/74 mmHg; P = 0.003/0.02) groups. Conclusions: Low adherence to an antihypertensivedrug regimen was associated with poor BP control.
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