Neurological deterioration in the treatment of Herpes zoster: encephalitis or neurotoxic effect of acyclovir?

Neurotoxicity associated with acyclovir and valacyclovir: A systematic review of cases

WHAT IS KNOWN AND OBJECTIVE

Acyclovir and valacyclovir are commonly used antivirals with good general tolerance. Despite their good safety profile, they can cause systemic adverse effects, such as neurotoxicity, which are less frequent and known. The objective of this review was to collect all the reported cases of neurotoxicity associated with acyclovir and valaciclovir published in the literature and characterize their clinical course and interventions.

METHODS

A systematic review of cases was carried out following the guidelines established by "Preferred Reporting Items for Systematic Reviews and Meta-Analyses" (PRISMA). The research was carried out using the PubMed-Medline and Embase databases, between July 1984 and March 2021.

RESULTS AND DISCUSSION

A total of 119 cases with neurotoxicity mainly related to acyclovir (n = 88; 73.9%), followed by valaciclovir (n = 35; 29.4%) were analysed. 49.6% (n = 59) were men with a mean age of 59.5 years ± 21.1 (0.5-88). In 83.3% of the cases, renal impairment was documented and 57.1% (n = 68) with end-stage renal disease. The administered dose was higher than the renal adjustment recommendations in 59.7% of the cases. The global mean of onset of symptoms was 3.1 days ± 4.3 (0.2-28) after the start of antivirals. The mean recovery time was 9.8 days ± 21.7 (0.2-180). 74.4% of the patients had a recovery of ≤7 days, 15.9% between 8 and 15 days and 9.8% > 15 days.

WHAT IS NEW AND CONCLUSION

The neurotoxicity induced by acyclovir and its derivative valacyclovir is a poorly known and rare adverse effect that can occur mainly in patients with advanced age and impaired renal function. The most characteristic symptoms are confusion, altered level of consciousness, hallucinations, agitation and dysarthria. The basis of treatment is the discontinuation of the antiviral, and in some cases, it may require additional clearance by dialysis.

A case of acyclovir neurotoxicity presenting with atypical cerebrospinal fluid findings

An 82-year-old man with a history of end-stage renal disease presented with progressively worsening confusion and somnolence for the past 4-5 days. The patient was diagnosed with herpes zoster by his primary care physician 5 days ago and was started on a course of valacyclovir 1 g three times a day (dose not adjusted for renal impairment).A lumbar puncture was performed and cerebrospinal fluid (CSF) studies revealed 37 white blood cells (WBCs)/hpf (100% monocytes), protein 64 mg/dL and glucose 52 mg/dL. He was started on ceftriaxone, ampicillin and acyclovir. MRI of the brain was done and was unremarkable. Acyclovir-induced encephalopathy was high on differential, but his CSF findings were concerning for viral encephalitis. Nonetheless, all antimicrobials were discontinued and he was scheduled for a 5-hour dialysis session. The very next day, he showed immense improvement and eventually recovered completely. CSF PCR tests for both herpes simplex virus and varicella zoster virus came back negative.