Clonidine: A new antihypertensive agent

Abstract

Intravenous administration of clonidine in hypertensive patients resulted in a short, hypertensive response followed by a prolonged reduction of both systolic and diastolic pressure. The antihypertensive response was associated with a decrease of total forearm blood flow, while the muscle blood flow of the calf was unchanged or moderately increased. Skin blood flow showed a sharp reduction initially, followed by a slow return to control levels. In patients with essential hypertension the reduction in blood pressure after acute oral administration of clonidine was associated with a decrease in cardiac output in the supine position. In contrast, in the upright position, a reduction in both cardiac output and total peripheral resistance were observed. During the antihypertensive response, renal blood flow and glomerular filtration rate were maintained, both acutely and chronically. Intravenous or intramuscular administration of clonidine proved to be very effective in hypertensive emergencies. In 174 hospitalized patients, prolonged oral administration resulted in significant improvement of the blood pressure in 61 percent of the cases. In 115 ambulatory patients, significant improvement occurred in 64 percent. Clonidine was added to the therapeutic regimen of 20 ambulatory patients who had remained hypertensive during diuretic therapy alone, and 16 (80 percent) of the 20 showed a significant antihypertensive response in both the supine and upright positions. The most common side effects were drowsiness and dryness of the mouth. Because of its marked efficacy and the beneficial cardiovascular and renal effects, clonidine represents a most useful addition to our antihypertensive armamentarium.