Acyclovir
ZOVIRAX
What it isGuanosine analog activated by viral thymidine kinase; herpes simplex, varicella, and zoster.
Why it mattersActivation only inside infected cells gives a wide safety margin, and IV acyclovir is the treatment for HSV encephalitis.
What it changesPoor oral bioavailability means five-times-daily dosing — valacyclovir solves this. Crystal nephropathy without hydration; renally adjusted.
FDA-approved for
- herpes/varicella (1982)
FDA label
Read the full label on DailyMed ↗
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Herpes zoster (acute) | Adult | 800 mg q4h (5×/day) | 800 mg q4h ×7–10 days | |
| Initial genital herpes | Adult | 200 mg q4h (5×/day) | 200 mg q4h ×10 days | |
| Chronic suppression, recurrent genital herpes | Adult | 400 mg BID | 400 mg BID up to 12 months (range 200 mg TID–200 mg 5×/day) | |
| Intermittent (recurrent) genital herpes | Adult | 200 mg q4h (5×/day) | 200 mg q4h ×5 days, start at prodrome | |
| Chickenpox | Children ≥2 yr (≤40 kg) | 20 mg/kg/dose QID | 20 mg/kg QID (max 80 mg/kg/day) ×5 days | 800 mg per dose |
| Chickenpox | Adults & children >40 kg | 800 mg QID | 800 mg QID ×5 days |
Renal Adjust for renal impairment per CrCl (e.g., 200 mg q4h regimen → 200 mg q12h if CrCl 0–10; 800 mg q4h regimen → q8h if CrCl 10–25, q12h if 0–10). Give a supplemental dose after hemodialysis.
Hepatic Undefined
Instructions
- Maintain adequate hydration.
- For zoster and chickenpox, start at the earliest sign/symptom.
- Administer an additional dose after each hemodialysis session; no supplemental dose needed for peritoneal dialysis.
Cautions
- Acute renal failure — ensure adequate hydration; higher risk with dehydration or pre-existing renal impairment.
- Neurologic effects (confusion, hallucinations, agitation, seizures, encephalopathy), especially in older adults or renal impairment.
- Severe cutaneous adverse reactions (SJS, TEN, AGEP, DRESS) and anaphylaxis reported.
- Thrombocytopenia/leukopenia and hepatitis reported.
Adverse reactions
- Nausea/vomiting, diarrhea
- Headache, malaise
- Rare: renal failure/renal pain
- Rare: neurologic effects (confusion, hallucinations, seizures)
- Rare: SJS/TEN/DRESS, anaphylaxis
Pregnancy Pregnancy exposure registry showed birth-defect rate approximating the general population; use only if potential benefit justifies risk (former Category B).
Lactation Undefined
NO BOXED WARNINGS
Principal riskCrystal nephropathy without adequate hydration
Cost, est. cash$10–$500/month
Generic entry1997
Classes and tags
Clinical profile
Legacy pregnancy categoryB
Defining liabilityAgent-specific renal, hepatic, hematologic, metabolic and drug-interaction toxicity.
Mechanism of action: Acyclovir ballicule
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