Acyclovir Dosing Adjustments in Renal Impairment
Acyclovir dosing must be reduced in patients with impaired renal function based on creatinine clearance, with specific dosage adjustments for each level of renal impairment. 1
Dosing Recommendations Based on Renal Function
Oral Acyclovir Dosing
| Creatinine Clearance | Normal Dose 200 mg q4h | Normal Dose 400 mg q12h | Normal Dose 800 mg q4h |
|---|---|---|---|
| >25 mL/min | 200 mg q4h | 400 mg q12h | 800 mg q4h |
| 10-25 mL/min | 200 mg q4h | 200 mg q12h | 800 mg q8h |
| <10 mL/min | 200 mg q12h | 200 mg q12h | 800 mg q12h |
Intravenous Acyclovir Dosing
For IV acyclovir, similar principles apply with dose reduction based on creatinine clearance. The dose of acyclovir should be adjusted according to the severity of renal impairment 2.
Special Considerations for Dialysis Patients
Hemodialysis
- Acyclovir is readily dialyzable with a mean plasma half-life of approximately 5 hours during hemodialysis 1, 3
- This results in a 60% decrease in plasma concentrations following a 6-hour dialysis period 1
- An additional dose should be administered after each dialysis session 1
- For patients on hemodialysis receiving oral acyclovir, 200 mg every 12 hours is recommended, with the first daily dose administered after dialysis 2
Peritoneal Dialysis
- No supplemental dose appears to be necessary after adjustment of the dosing interval 1
- However, caution is advised as neurotoxicity has been reported in peritoneal dialysis patients even with reduced dosing 4
Pharmacokinetic Considerations
Acyclovir is primarily eliminated unchanged via the kidneys through both glomerular filtration and tubular secretion 5. In patients with normal renal function, the mean half-life is approximately 2.5 hours, but this increases significantly in renal impairment 5:
- In end-stage renal disease, the half-life extends to approximately 19.5 hours 3
- During hemodialysis, the half-life is reduced to approximately 5.7 hours 3
Monitoring and Safety Considerations
- Monitor for neurological symptoms (confusion, hallucinations, seizures), which may indicate acyclovir neurotoxicity, especially in patients with severe renal impairment 4
- Ensure adequate hydration to prevent crystalluria, particularly in patients with compromised renal function 2
- Regular assessment of renal function is recommended during treatment 2
Clinical Pearls
- The bioavailability of oral acyclovir is approximately 20%, which means that IV doses are roughly 5 times more potent than equivalent oral doses 5
- Acyclovir and its metabolites achieve higher concentrations in both plasma and CSF in patients with renal impairment, which may contribute to increased risk of neurotoxicity 6
- For patients with end-stage renal failure with varicella zoster infections, a loading dose of 400 mg followed by 200 mg twice daily has been suggested as a safer regimen 4
Remember that appropriate dosing adjustments are critical to prevent accumulation of acyclovir and its metabolites, which can lead to serious neurological complications in patients with impaired renal function.