Hormonal and hemodynamic effects of short- and long-term clonidine therapy in patients with mild-to-moderate hypertension.

Two studies of the responses to clonidine as the sole antihypertensive drug in the treatment of mild-to-moderate hypertension are reported. In the first, 11 patients with mild hypertension were treated with 0.1 mg clonidine twice daily for eight weeks. Those patients with "low renin" hypertension (n = 7) were noted to show an increase in plasma renin activity; the patients with "normal renin" hypertension (n = 4) tended to show a decrease. Both groups had a similar decrease in blood pressure. The changes in renin activity correlated significantly (p less than 0.01) with the small changes in endogenous creatinine clearance (r = 0.84). In the second study, 16 patients with mild-to-moderate essential hypertension were treated for three months with 0.2 mg clonidine three times daily. Blood pressure decreased from 167 +/- 4/105 +/- 2 to 140 +/- 3/90 +/- 2 mm Hg (p less than 0.01). Blood pressure changes correlated with decreases in plasma catecholamines (r = 0.61, p less than 0.001) and heart rate (r = 0.78, p less than 0.001). No significant changes in cardiac output, blood volume, renal blood flow, or glomerular filtration rate were noted. Clonidine is an effective and safe therapy when used as the sole medication in treating mild-to-moderate hypertension.