A Curious Case of Purple Chromaturia.

Hydroxocobalamin, an antidote for cyanide toxicity, is known for its safety and efficacy. A notable side effect is dark red to purple chromaturia, sometimes mimicking hematuria. We report the case of a middle-aged female exposed to smoke inhalation following a house fire, who was treated on-site by emergency medical services with oxygenation and intravenous hydroxocobalamin and developed purple urine shortly after admission. Hematuria, hemolysis, rhabdomyolysis, and renal impairment were excluded with appropriate workup. The discoloration resolved spontaneously over five weeks without intervention, consistent with hydroxocobalamin-induced chromaturia. While benign and self-limiting, this phenomenon may cause diagnostic confusion and patient concern. Awareness of this side effect can prevent unnecessary investigations and reassure patients about its transient nature.