Antihypertensive effects and plasma levels of guanfacine in man

Usefulness of low dose guanfacine, once a day, for 24-hour control of essential hypertension

The 24-hour duration of the antihypertensive effect of guanfacine, a centrally acting alpha 2-adrenoceptor agonist administered once a day, was demonstrated in a 12-week, multicenter, double-blind, placebo-controlled study. Two hundred and forty-nine patients who remained mildly to moderately hypertensive following a 5-week period, during which they had been weaned from previous antihypertensive medications and stabilized on 25-mg chlorthalidone taken once a day, were involved. Of the 249 patients, 126 received guanfacine as a step-2 agent and 123 received placebo. Both groups were further subdivided so that blood pressure (BP) measurements were determined either 12 or 24 hours after dosing. The initial dose of guanfacine was 1 mg/day, which could be raised 1 mg at 2-week intervals to a maximum daily dose of 3 mg/day at the discretion of each investigator. The daily dose could also be lowered by 1 mg at 2-week intervals, depending on patient response. The mean 24-hour reductions with guanfacine in sitting diastolic BP (-11 mm Hg), systolic BP (-14 mm Hg) and mean arterial pressure (-12 mm Hg) were statistically significant (p less than 0.01) compared with the reductions in BP with placebo. Heart rate also decreased with guanfacine, but no clinically relevant bradycardia (less than 60 beats/min) was observed. Dry mouth (47%), constipation (16%), fatigue (12%) and drowsiness (4%) were the most frequently reported side effects. The highly acceptable side-effects profile of guanfacine was also indicated by the small percentage of patients (7%) who prematurely left the study because of adverse reactions.