A Dose Too Far: Valacyclovir’s Surprising Side Effect

Valacyclovir, a prodrug of acyclovir, is a widely prescribed antiviral medication known for its efficacy in treating herpes infections. Although generally considered safe, rare cases of psychiatric adverse effects, including psychosis, have been reported. The precise mechanism underlying valacyclovir-induced psychosis remains unclear, but proposed explanations include potential neurotoxicity and alterations in neurotransmitter activity. Importantly, such adverse effects have been documented even in patients with normal renal function. Given that valacyclovir's pharmacokinetics are significantly altered in individuals with renal impairment - characterized by reduced clearance and prolonged half-life - the risk of drug accumulation and subsequent neurological complications is heightened in this population. Here, we present a unique case of valacyclovir-induced psychosis in a patient with pre-existing renal failure, emphasizing the importance of considering renal function when prescribing and monitoring this medication to mitigate the risk of psychiatric complications.