Effects of guanabenz on sodium and water homeostasis.

Sodium retention may partially offset the therapeutic action of some antihypertensive agents. To assess the effects of guanabenz on sodium balance, six men with mild to moderate hypertension were placed on diets with constant sodium intake (120 mEq/day) for approximately 4 weeks. After achieving sodium balance, the subjects received guanabenz (16-24 mg daily) for approximately 2 weeks. Mean supine blood pressure decreased from 144/93 to 133/86 mmHg during guanabenz treatment (p less than 0.001). Guanabenz therapy was associated with a decrease in body weight (mean +/- SE) from 85.4 +/- 7.0 to 84.4 +/- 6.8 kg (p less than 0.01). Sodium balance, glomerular filtration rate, plasma renin activity, mean maximal urine osmolality, fluid intake, urine volume, and serum sodium concentration were unchanged during guanabenz therapy. Three additional balance studies were performed during a period of greater sodium intake (180 mEq/day). Although higher doses of guanabenz were required to achieve blood pressure control, sodium balance still was not affected by the drug. Thus, an effective therapeutic dose of guanabenz administered for 2 weeks had no clinically significant effects on sodium or water homeostasis in patients with mild to moderate hypertension.