A three-phase clinical evaluation of prazosin.

A preliminary study of cardiac hemodynamics with measurement in both supine and tilt positions showed that the antihypertensive effect of prazosin given intravenously is associated with a fall in total peripheral resistance, with minor effects on cardiac output and heart rate, and with no consistent orthostatic hypotension. The postural reflexes appear to remain intact. The results are entirely similar to those reported by Lund-Johansen. In a second, short-term study of ambulatory patients, prazosin alone exerted an antihypertensive effect somewhat less than that of methyldopa, but the difference in blood pressure reduction between supine and standing positions was less with prazosin than with methyldopa. Both drugs were well tolerated. In a third, long-term study, prazosin alone gave satisfactory antihypertensive results, and prazosin used in combination with polythiazide produced a satisfactory response in 80% of the patients.