Section 15 · Monograph
Acyclovir
Reviewed Nov 2026FDA label
ZoviraxAntiviral
- Forms
- IV: 50mg/mL
- Dose
- HSV encephalitis: 10mg/kg IV q8h for 14-21 days (adjust for renal function; hydrate)
- MOA
- Inhibits viral DNA polymerase
Indications
- Herpes simplex encephalitisFDA-labeled
- Mucocutaneous HSV, varicella-zoster, and neonatal herpes infectionsFDA-labeled
Mechanism of Action
- Guanosine analog phosphorylated by viral thymidine kinase; inhibits viral DNA polymerase and terminates DNA chain elongation
Full Dosing
Adult / usual
- HSV encephalitis: 10mg/kg IV every 8 hours for 14-21 days (adults); neonates 20mg/kg every 8 hours for 21 days
- Start empirically while awaiting CSF HSV PCR
Renal
- Infuse over 1 hour; ensure hydration; adjust dose for creatinine clearance
Contraindications
- Hypersensitivity to acyclovir or valacyclovir
Drug Interactions
- Nephrotoxic drugs (aminoglycosides, amphotericin B, contrast) increase kidney injury risk
- Probenecid increases acyclovir levels
- Mycophenolate competes for renal tubular secretion
Adverse Effects
- Acute kidney injury from crystal nephropathy — hydrate
- Neurotoxicity (confusion, tremor, hallucinations, seizures), especially in renal impairment
- Phlebitis at IV site
- Nausea, rash
Monitoring Parameters
- Creatinine and BUN, urine output
- Hydration status
- Mental status
Pregnancy & Lactation
- Limited data; used in pregnancy when indicated
- Excreted in milk; generally considered compatible