Prolonged hypotension after initial minoxidil dose.

Severe prolonged hypotension developed in a hypertensive patient several hours after the initial doses of minoxidil therapy. Hemodynamic measurements revealed a markedly low systemic vascular resistance and a markedly high cardiac output. Other causes of hypotension were ruled out. The patient's hemodynamic abnormalities lasted three days after minoxidil therapy was discontinued, and she then reverted to hypertension. Thus, a 10-mg starting dose of minoxidil may produce profound life-threatening hypotension, which can last up to 72 hours.