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October 1983

Prazosin-Induced Bradycardia in Acute Treatment of Hypertension

Arch Intern Med. 1983;143(10):2019-2023. doi:10.1001/archinte.1983.00350100203049

To the Editor.  —Prazosin hydrochloride is a quinazolone derivative that has been shown to lower the BP by exerting a vasodilator effect on the resistance and capacitance vessels, resuiting from selective neuromuscular postsynaptic α-blockade.1 A notable peculiarity of therapy with this drug is the absence of reflex tachycardia, which is commonly encountered with the use of other peripheral vasodilators.1 A direct negative chronotropic effect of prazosin has been previously reported in experimental animals2,3 and in one clinical study of patients with severe heart failure.4The occurrence of a negative chronotropic effect of prazosin during the short-term treatment of hypertension has been overlooked. We recently used 2 mg of oral prazosin hydrochloride to achieve a rapid BP reduction in a group of 17 consecutively seen patients who had been referred to the emergency room for severe hypertension. Within three hours, concomitant to the drop in BP, 13 patients