Orthostatic hypotension occurring after discontinuation of long-term minoxidil therapy.

Minoxidil (Loniten), a potent predominant arteriolar vasodilator, provides prompt and effective reduction of blood pressure in many patients with severe hypertension. Minoxidil results, however, in profound reflex tachycardia and increased plasma volume almost always necessitating concomitant use of beta-adrenergic blocking agents and diuretics. Hypertrichosis and massive fluid retention are troublesome adverse reactions that may require discontinuation of minoxidil and initiation of an alternative antihypertensive agent. When minoxidil is discontinued, diuretic dosage requires re-evaluation and possible tapering to prevent volume depletion. Volume depletion is a risk factor in patients with persistent peripheral edema, sodium deprivation or dehydration; these states may interfere with physiologic mechanisms that maintain adequate cerebral perfusion upon standing, triggering orthostatic hypotension and potential syncope. Hypertension clinic visits should routinely include supine followed by sitting and standing blood pressure determinations to ensure detection of orthostatic hypotension. Described in the article is a case study in which a patient developed severe orthostatic hypotension one month after minoxidil was discontinued. Pathophysiologic mechanisms are discussed.