Impact of continuous hemodiafiltration on serum acyclovir concentrations in a patient with encephalopathy

Reports on serum acyclovir (ACV) concentrations in patients undergoing continuous hemodiafiltration (CHDF) remain limited. We present a case describing the impact of CHDF on serum ACV levels in a patient with encephalopathy. A Japanese woman in her 70s was prescribed oral valacyclovir (VACV) at a dose of 1000 mg three times daily for herpes zoster ophthalmicus. After 7 days of treatment, she was admitted to a local hospital with fever, dysarthria, altered consciousness, hallucinations, and headache. Her serum creatinine level was elevated at 4.02 mg/dL. Intravenous ACV was initiated under the clinical suspicion of varicella zoster virus (VZV) encephalitis. However, after 3 days of treatment without improvement in consciousness, she was transferred to our hospital. Her serum ACV concentration upon admission was 14.1 μg/mL. Suspecting ACV-induced encephalopathy and renal dysfunction, CHDF was promptly initiated. Following CHDF therapy, serum ACV levels declined rapidly, accompanied by a gradual improvement in consciousness. This case suggests that CHDF may be an effective therapeutic option for managing ACV-associated nephropathy and encephalopathy.