STUDIES WITH PRAZOSIN—A NEW EFFECTIVE HYPOTENSIVE AGENT. II

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Abstract
Twenty‐two hypertensive patients were given 40 mg of propranolol thrice daily and 0.5 g of chlorothiazide twice daily. Of these patients, only ten had diastolic blood pressure remaining above 100 mm Hg. They were allocated at random to a double‐blind phase in which treatment with identical capsules containing 1 mg of prazosin or 25 mg of hydralazine was added. Patients were followed for two 12‐week periods in a cross‐over study, receiving either prazosin or hydralazine in a dose sufficient to lower the diastolic blood pressure below 95 mm Hg. Eight patients completed the study. In seven patients, the diastolic blood pressure was reduced to below 95 mm Hg by the addition of either prazosin or hydralazine. One patient whose blood pressure could not be controlled with the maximum dose of either prazosin or hydralazine responded to a combination which included both drugs. Twenty‐four other patients receiving either prazosin or hydralazine in combination with other antihypertensive agents were allocated at random to a double‐blind phase of treatment with identical capsules containing either 1 mg of prazosin or 25 mg of hydrallazine after an initial control period. The dose was adjusted to achieve optimum control over two six‐week periods in a cross‐over study. Eight patients were withdrawn because of side effects; seven were taking hydrallazine and one was taking prazosin. For a given degree of control of supine diastolic blood pressure, prazosin produced a greater fall in standing diastolic blood pressure. The “dose equivalence” between hydrallazine and prazosin —that is, the dose required to achieve a similar control of the supine diastolic blood pressure—was 1 mg of prazosin to 20 mg of hydrallazine. Blood pressure control was maintained in 12 patients who participated in a further phase in which both prazosin and hydrallazine were combined in half their respective optimum doses.