Minoxidil Overdose: A Case Report and Review of the Literature

Minoxidil is a potent vasodilator originally used to treat severe refractory hypertension. Hypertrichosis is a common side effect of minoxidil, which led to the development and marketing of topical preparations for treating androgenetic alopecia (AGA). Minoxidil is primarily used to treat AGA; however, its inappropriate use can cause systemic side effects. Herein, we present the case of a 61-year-old Japanese man with an overdose of oral minoxidil that led to hypotension, breathlessness, edema, weight gain, and facial flushing. As the vital signs and results of laboratory and imaging tests were generally normal, no treatment was initiated. Two weeks after the initial visit, the patient's body weight decreased by approximately 10 kg, and the edema disappeared. To date, 14 patients have been reported to have developed systemic side effects following an overdose of minoxidil-containing medications. Our literature review identified that systemic symptoms related to minoxidil overdose occurred in 10 of 14 patients after ingestion of a topical formulation, three after tablet ingestion, and one after application of a large amount of topical solution to the scalp. All 14 patients experienced hypotension and/or tachycardia. These symptoms occurred within six hours of the ingestion of 100-3000 mg minoxidil. One of 14 patients presented with a complication of myocardial infarction, and no patient died. Interestingly, fluid therapy was ineffective in the treatment of hypotension related to minoxidil overdoses. Since the primary pathophysiological effect of minoxidil is a decrease in systemic vascular resistance by arteriolar vasodilation, peripherally acting alpha-adrenergic agonists, such as phenylephrine, midodrine, and norepinephrine, may be safer and more effective than dopamine and epinephrine.