Contraindications to Acyclovir
Acyclovir is contraindicated in patients who develop hypersensitivity to acyclovir or valacyclovir. 1
Primary Contraindications
- Hypersensitivity reactions: The only absolute contraindication to acyclovir is a history of hypersensitivity to acyclovir or its prodrug valacyclovir 1
Relative Contraindications and Special Considerations
Renal Impairment
- Pre-existing renal dysfunction: Requires dose adjustment as acyclovir is primarily excreted via the kidneys through glomerular filtration and tubular secretion 2
- Risk of nephropathy: Acyclovir can cause renal impairment through crystalluria and obstructive nephropathy, which typically manifests after 4 days of intravenous therapy and can affect up to 20% of patients 2
- End-stage renal disease: Patients with end-stage renal disease are at particularly high risk for neurotoxicity 3
Neurological Considerations
- Neurotoxicity risk: Patients with renal impairment are at increased risk for acyclovir-induced neurotoxicity, which can present as confusion, altered level of consciousness, hallucinations, agitation, and dysarthria 3, 4
- Advanced age: Elderly patients have increased susceptibility to neurotoxic effects, especially when combined with renal impairment 3
Monitoring and Management Recommendations
For Patients with Renal Impairment
- Monitor renal function at initiation of treatment and once or twice weekly during treatment 2
- Maintain adequate hydration to reduce risk of nephropathy 2
- Adjust dosage based on creatinine clearance 5
For IV Administration
- Avoid rapid bolus administration, which increases risk of crystalluria 6
- Monitor for signs of infusion site inflammation 6
Clinical Pearls and Pitfalls
- Common pitfall: Failure to adjust dosing in patients with renal impairment, which can lead to serious neurotoxicity 4
- Important consideration: Even with appropriate dosing, acyclovir can accumulate in patients with renal dysfunction, requiring careful monitoring 3
- Duration of treatment: For HSV encephalitis, treatment should continue for 14-21 days, with consideration of repeat CSF testing to confirm viral clearance 2
- Empiric use caution: Unnecessary or prolonged empiric use of acyclovir should be avoided when alternative diagnoses become apparent 7
By carefully considering these contraindications and special precautions, clinicians can maximize the therapeutic benefits of acyclovir while minimizing potential adverse effects.