Studies with prazosin--a new effective hypotensive agent. III. An acute double-blind cross-over study comparing the effects of single doses of prazosin and hydrallazine in combination with propranolol and a diuretic.

The duration of action of a single dose of prazosin and hydrallazine on blood pressure and heart rate was studied in 16 hypertensive patients whose blood pressure was not adequately controlled by a combination of a thiazide diuretic and a beta-adrenergic blocking agent, and had required the addition of either prazosin or hydrallazine. Observations over an eight-hour period, after a single dose of either 3 mg of prazosin, or 75 mg of hydrallazine, in identical capsules, with cross-over study one week later, showed significant reductions in blood pressure within the first hour after oral administration of either agent. This reduction in blood pressure persisted for four to six hours after hydrallazine and six to seven hours after prazosin administration. Tachycardia was more pronounced and prolonged after hydrallazine administration and side effects were more common.