Neurologic Acyclovir Toxicity Despite Normal Renal Function
INTRODUCTION: Acyclovir is an antiviral medication commonly prescribed for herpes simplex virus, cytomegalovirus, and varicella zoster virus (which manifests as chickenpox and shingles). The drug acts as a nucleotide analog and inhibits viral replication. In the U.S., 1 million cases of shingles are reported every year and result in nearly one billion dollars in health care expenses annually. Due to the prevalence of acyclovir use, physicians should be aware of the potential for neurotoxicity, which while rare, is typically diagnosed in patients who have chronic kidney disease or acute kidney injury.
CASE HISTORY: We report a case of neurotoxicity in a 63 year-old male patient with normal renal function. The fatigued patient presented with altered mental status as well as neurological manifestations including global ataxia and aphasia. The lack of abnormal imaging studies and lumbar puncture cerebral spinal fluid analysis raised suspicion of antiviral toxicity. Subsequent clinical improvement following withdrawal of the antiviral led to the conclusion of acyclovir induced encephalopathy.
DISCUSSION: In patients taking acyclovir, common causes of neurological impairment include viral encephalitis, meningitis, ischemic stroke or acyclovir toxicity. Acyclovir is a renally excreted compound. Thus, in patients with impaired renal function, toxicity may develop. For patients with normal renal function toxicity may be attributed to decreased muscle mass, insufficient fluid intake or overdose. As the incidence of viral diseases treated with acyclovir increases, atypical neurotoxic reactions should be considered even for patients with normal renal function, as early detection will prevent sustained neurologic impairment.