When A Seemingly Harmless Prescription Turns Into Toxicity

Valacyclovir neurotoxicity is commonly seen in the elderly and those with impaired renal function. Differential diagnosis can be challenging as a myriad of medical conditions, including herpes zoster virus associated encephalitis, may present in a similar fashion. We present a case of a 71-year-old male who presented with altered mental status in the setting of recent herpes zoster eruption. I its condition was attributed to valacyclovir neurotoxicity, and initiation of appropriate supportive therapy was met with complete resolution of symptoms and normalization of cognitive function.