Valacyclovir-induced Neurotoxicity in a Patient with a Preserved Renal Function

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Valacyclovir, a prodrug of acyclovir, is the first-line treatment for herpes zoster, but the renal function must be monitored, because acyclovir is metabolized by the kidneys. We herein report a case of valacyclovir-induced neurotoxicity with no preceding renal impairment. An 88-year-old man was admitted because of an impaired consciousness after the administration of valacyclovir at 3,000 mg daily for herpes zoster on the chest. His consciousness level gradually improved with hydration and valacyclovir withdrawal. It was later confirmed that the level of acyclovir on admission had been 35.45 μg/mL in the blood and 36.45 μg/mL in the cerebrospinal fluid.