| Summary: | Case A 47‐year‐old man ingested 60 mL of a topical solution (3,000 mg minoxidil) and presented with prolonged hypotension. Treatment with dopamine hydrochloride and noradrenaline provided blood pressure control. Serum unchanged minoxidil concentrations at 4 and 16 h after ingestion were 4,994 and 33.9 ng/mL, respectively. Urine concentrations of unchanged minoxidil, minoxidil‐O‐glucuronide, and minoxidil‐N‐O‐sulfate at 16 h after ingestion were 360.4, 1,953, and 104.5 ng/mL, respectively. Outcome The serum unchanged minoxidil concentration rapidly decreased over a short interval. However, the patient needed to receive vasopressor support for the first 4 days after being admitted to the hospital. The urine minoxidil‐O‐glucuronide concentration was higher than the concentrations of unchanged minoxidil and minoxidil‐N‐O‐sulfate. Conclusion Although the serum concentration of unchanged minoxidil rapidly decreased, ingesting large amounts of a topical minoxidil solution can have serious and prolonged cardiovascular effects. Analyzing the minoxidil‐O‐glucuronide concentration in urine is useful for diagnosing minoxidil poisoning.
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