Acyclovir Renal Dose Adjustment
For patients with renal impairment, acyclovir requires dose reduction based on creatinine clearance, with oral dosing adjusted to 200 mg every 12 hours for CrCl <10 mL/min and intravenous dosing reduced to 2.5-5 mg/kg every 24 hours for the same level of renal function, with supplemental dosing required after each hemodialysis session. 1, 2
Oral Acyclovir Dosing Adjustments
Standard Dosing by Indication and Renal Function
For CrCl >10 mL/min: Standard dosing applies based on indication (200 mg every 4 hours for genital herpes, 400 mg every 12 hours for suppressive therapy, or 800 mg every 4 hours for herpes zoster) 2
For CrCl <10 mL/min: Reduce all oral regimens to 200 mg every 12 hours regardless of indication 1, 2
For hemodialysis patients: Administer 200 mg every 12 hours, with the first daily dose given after dialysis 1, 2
Specific Adjustments by Standard Regimen
200 mg every 4 hours regimen: No adjustment needed for CrCl >10 mL/min; reduce to 200 mg every 12 hours for CrCl 0-10 mL/min 2
400 mg every 12 hours regimen: No adjustment needed for CrCl >10 mL/min; reduce to 200 mg every 12 hours for CrCl 0-10 mL/min 2
800 mg every 4 hours regimen: No adjustment for CrCl >25 mL/min; reduce to 800 mg every 8 hours for CrCl 10-25 mL/min; reduce to 800 mg every 12 hours for CrCl 0-10 mL/min 2
Intravenous Acyclovir Dosing Adjustments
Dose Reduction by Creatinine Clearance
For CrCl 25-50 mL/min: Reduce to 5-10 mg/kg IV every 12 hours 1
For CrCl 10-24 mL/min: Reduce to 5-10 mg/kg IV every 24 hours 1
For CrCl <10 mL/min: Reduce to 2.5-5 mg/kg IV every 24 hours 1
Hemodialysis Considerations
Timing of administration: Administer the dose post-dialysis on dialysis days, as hemodialysis removes approximately 60% of acyclovir over a 6-hour dialysis period with a dialysis clearance of 81.8 mL/min 1, 3
Supplemental dosing: An additional dose is required after each dialysis session 1, 2
Terminal half-life during dialysis: Acyclovir half-life decreases from 19.5 hours in anuric patients to 5.7 hours during hemodialysis 3
Critical Administration Guidelines to Prevent Nephrotoxicity
Infusion Rate and Hydration
Avoid rapid IV bolus: Administer IV acyclovir as a slow infusion over 1 hour to prevent crystalluria and acute renal failure 1
Ensure adequate hydration: Maintain at least 1.5 liters of water intake daily during treatment 1
Monitor renal function: The risk of acyclovir-induced nephrotoxicity increases with bolus administration and inadequate hydration 4, 5
Common Pitfalls and Caveats
Neurotoxicity Risk in Renal Failure
Increased risk with impaired clearance: Patients with end-stage renal disease have a terminal plasma half-life of 19.5 hours (compared to 2-3 hours in normal renal function), leading to drug accumulation and potential neurotoxicity if doses are not adjusted 3, 6
Clinical presentation: Neurotoxicity manifests as reversible neuropsychiatric symptoms and occurs more frequently when standard doses are used in renal impairment 7, 6
CSF penetration: While renal impairment does not alter the CSF-to-plasma ratio, the higher systemic concentrations result in proportionally higher CSF concentrations, increasing neurotoxicity risk 7