Published: 5 December 2024

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Aciclovir and valaciclovir: toxic in renal impairment

Prescriber Update 45(4): 90
December 2024

This article is a reminder about using aciclovir, and its prodrug valaciclovir, in patients with renal impairment.

Aciclovir and valaciclovir

Aciclovir and valaciclovir are antiviral medicines used to prevent and/or treat viral infections, including herpes simplex, varicella zoster and cytomegalovirus (CMV).¹ Aciclovir is available in intravenous (IV) and oral formulations, while valaciclovir is available only in oral form.

Oral aciclovir has low bioavailability. Valaciclovir is a prodrug of aciclovir designed to increase bioavailability. IV aciclovir has the greatest bioavailability and is recommended for treatment of severe infections.^1,2

Neurotoxicity with renal impairment

Aciclovir is eliminated by renal clearance, involving both glomerular filtration and tubular secretion. Aciclovir can therefore accumulate in patients with renal impairment.^1,3,4

High blood levels of aciclovir can result neurotoxicity.¹

Aciclovir readily crosses the blood-brain barrier. In patients with renal impairment, the medicine levels can increase and cause neurotoxicity.¹ Symptoms may include lethargy, confusion, hallucinations, agitation, seizures and coma, and are generally reversible upon discontinuation of treatment.^1,3,4

Prescribing considerations

Assess the patient’s renal function before prescribing aciclovir or valaciclovir. Reduce the dose and/or frequency according to the level of impairment. Refer to the recommendations in the respective data sheets.

• Search for a data sheet

During treatment, ensure adequate hydration and monitor patients for neurological adverse effects.^3,4

References

1. Brandariz-Nuñez D, Correas-Sanahuja M and Maya-Gallego S. 2021. Neurotoxicity associated with acyclovir and valacyclovir: A systematic review of cases. Journal of Clinical Pharmacy and Therapeutics 46: 918–26. DOI: https://doi.org/10.1111/jcpt.13464 (accessed 24 September 2024).
2. Larsen F. 2004. Aciclovir. In: DermNet. URL: dermnetnz.org/topics/aciclovir (accessed 30 October 2024).
3. Baxter Healthcare Ltd. 2024. Aciclovir-Baxter New Zealand Data Sheet 11 April 2024. URL: medsafe.govt.nz/profs/Datasheet/A/AciclovirClaris.pdf (accessed 24 September 2024).
4. Viatris Ltd. 2024. Vaclovir New Zealand Data Sheet 5 July 2024. URL: medsafe.govt.nz/profs/Datasheet/v/vaclovirtab.pdf (accessed 24 September 2024).