How Acyclovir Causes Kidney Damage
Acyclovir, an antiviral used for herpes infections, can form crystals in kidney tubules, leading to acute kidney injury. This happens because the drug and its metabolites have low solubility in urine, especially when concentrated.[1]
Patient Factors That Raise Risk
- Dehydration or low urine output: Reduces kidney blood flow and urine dilution, allowing crystals to precipitate. Common in febrile patients or those with vomiting/diarrhea.[1][2]
- Advanced age: Older adults (over 60) have slower kidney function and less muscle mass, increasing drug accumulation.[2][3]
- Pre-existing kidney disease: Conditions like chronic kidney disease or reduced glomerular filtration rate (GFR <50 mL/min) impair drug clearance.[1][3]
- High body weight or obesity: May require higher doses, leading to greater drug exposure without proportional kidney function adjustment.[2]
Dosing and Administration Issues
- High or rapid IV doses: Bolus infusions (>10 mg/kg/hour) spike blood levels, overwhelming kidney excretion. Continuous infusion over 1 hour lowers risk.[1][2]
- Excessive total daily dose: Over 25-30 mg/kg/day, especially without dose adjustment for kidney function.[3]
- Oral overuse: Less common but possible in renal impairment if not reduced (e.g., >800 mg five times daily).[1]
Drug Interactions and Combinations
- Nephrotoxic drugs: Concurrent use with aminoglycosides (gentamicin), amphotericin B, cyclosporine, or NSAIDs amplifies tubular damage.[2][3]
- Probenecid: Inhibits acyclovir secretion, raising levels.[1]
Treatment and Monitoring Strategies to Mitigate Risk
Hydrate patients aggressively (2-3 L/day IV fluids) before and during therapy to maintain urine output >100 mL/hour. Adjust doses by CrCl: e.g., 50% reduction if CrCl 25-50 mL/min. Monitor serum creatinine daily during IV use, especially in at-risk groups.[1][2][3]
[1]: FDA Label - Acyclovir (Zovirax)
[2]: UpToDate - Acyclovir nephrotoxicity
[3]: Medscape - Acyclovir Dosing and Toxicity