A Rare Case of Severe Hyponatremia Associated with Acyclovir Use and Exacerbated by Furosemide

Hyponatremia, a common electrolyte disorder, is rarely associated with acyclovir therapy. We report a 64-year-old woman with a history of hypertension and type 2 diabetes mellitus who presented with altered mental status and severe hyponatremia (serum sodium: 112 mmol/L) after receiving acyclovir for herpes zoster and a single dose of intravenous furosemide. Initial management with hypertonic saline and fluid restriction failed to improve her condition. Acyclovir was subsequently discontinued, leading to a gradual resolution of hyponatremia and normalization of sodium levels. This case underscores the potential role of acyclovir in inducing hyponatremia, possibly through syndrome of inappropriate antidiuretic hormone secretion (SIADH), and highlights the importance of recognizing and managing this rare but serious adverse effect.