Acyclovir is a nucleoside analogue antiviral, the treatment of choice for herpesvirus infections (HSV-1, HSV-2, VZV). It is widely used for genital herpes, herpes zoster, and prophylaxis in immunocompromised patients.
Also known as: Zovirax, Aciclovir
Antiviral + uricosuric: acyclovir levels increased ~40% via blockade of renal tubular secretion.
Probenecid blocks renal tubular secretion of acyclovir via OAT1/OAT3 transporters, increasing serum levels by ~40% and prolonging half-life. Although the increase is moderate, acyclovir has a narrow therapeutic index — nephrotoxicity (tubular crystals) may be precipitated. Strategy: if coadministration necessary, reduce acyclovir dose by 50% and increase oral hydration to >2 L/day. Monitor creatinine and urine volume.
Antiviral + uricosuric: acyclovir ~40% via tubular secretion blockade.
Probenecid blocks renal tubular secretion of acyclovir, increasing serum levels by ~40% and prolonging half-life. Increased risk of nephrotoxicity (acyclovir crystals).
Creatinine, GFR, urine volume, nephrological symptoms.
If coadministration necessary: reduce acyclovir dose by 50% and increase hydration. Monitor GFR and creatinine.
DailyMed/FDA (NIH/NLM) — approved Acyclovir label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=cb64dfab-52ee-4312-bc9c-c3d04efe9109
Food does not significantly affect acyclovir absorption. May reduce nausea.
May be taken with or without food. Food helps reduce nausea.
Renal excretion >90% unchanged. Prolonged half-life (up to 20 h in anuria). Risk of crystalluria and nephrotoxicity.
eGFR 50-80: q8h. eGFR 20-50: q12h. eGFR 10-20: q24h. eGFR <10: q24h with 50% dose reduction. Haemodialysis: add post-HD dose.
DailyMed/FDA (NIH/NLM) — approved Acyclovir label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=cb64dfab-52ee-4312-bc9c-c3d04efe9109
Category B: safe. Treatment of choice for genital herpes and zoster in pregnancy.
All trimesters. Safe.
Excreted in low concentrations (<1% of dose). Compatible with breastfeeding.
No evidence of effects on fertility.
DailyMed/FDA (NIH/NLM) — approved Acyclovir label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=cb64dfab-52ee-4312-bc9c-c3d04efe9109
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Selective antiviral: active only in herpesvirus-infected cells (HSV-1, HSV-2, VZV). Inhibits viral replication with minimal toxicity to normal host cells.
Phosphorylated in 3 steps: viral thymidine kinase (1st phosphorylation) → cellular phosphotransferases (2nd and 3rd). Acyclovir triphosphate competes with dGTP for viral DNA polymerase and terminates viral DNA chain.
Oral bioavailability: 15-30% (dose-dependent). Peaks in 1-2 h. Wide distribution (body fluids, CSF ~50% of serum, skin).
Minimal metabolism: ~15% converted to ACV (9-carboxymethoxymethylguanine) hepatically. Most excreted renally unchanged.
2.5-3.5 h (normal renal function). 20 h in severe renal impairment (anuria).
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
