Acyclovir
ZOVIRAX
Pronunciation: ay-SYE-kloe-veer
“A cycling Zoo virus”
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.
Available strengths
- cap 200 mg
- tab 400, 800 mg
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
Cost
Generic entry1997
NO BOXED WARNINGS
Principal riskCrystal nephropathy without adequate hydration
Classes and tags
Clinical profile
Legacy pregnancy categoryB
Defining liabilityAgent-specific renal, hepatic, hematologic, metabolic and drug-interaction toxicity.
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