Acyclovir dosage
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acyclovir dosage indications 2024 guidelines
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Here is a comprehensive dosage reference for acyclovir, compiled from Harrison's (22nd ed., 2025), Goodman & Gilman's, and other authoritative sources:
Acyclovir Dosage Reference
Mechanism
Acyclovir is a guanosine analogue that requires phosphorylation by viral thymidine kinase (TK) first, then by host cell enzymes to its active triphosphate form. The triphosphate inhibits viral DNA polymerase and causes premature chain termination. Uninfected cells phosphorylate very little acyclovir, giving the drug its selective antiviral activity. - Harrison's 22E
Adult Oral Dosing
| Indication | Dose | Duration |
|---|---|---|
| Initial genital HSV | 200 mg 5x/day OR 400 mg 3x/day | 7-10 days |
| Recurrent genital HSV | 200 mg 5x/day OR 400 mg 3x/day OR 800 mg 3x/day for 2 days | 5 days |
| HSV suppression (chronic) | 400 mg twice daily | Up to 12 months, then reassess |
| Herpes zoster (VZV) | 800 mg 5x/day | 7-10 days |
| Varicella (chickenpox) - adults/adolescents | 800 mg 5x/day (start within 24 h of onset) | 5-7 days |
| HSV encephalitis (after IV, step-down) | 800 mg 5x/day | Complete 14-21 days total |
Note: VZV is less susceptible than HSV to acyclovir, so substantially higher doses are needed for VZV infections. Valacyclovir and famciclovir are generally preferred over oral acyclovir for herpes zoster due to better pharmacokinetics (3-5x higher bioavailability). - Goodman & Gilman's, Harrison's 22E
Adult IV Dosing
| Indication | Dose | Duration |
|---|---|---|
| HSV encephalitis (adults) | 10 mg/kg IV q8h (30 mg/kg/day total) | 21 days |
| Severe/disseminated HSV (immunocompromised) | 5-10 mg/kg IV q8h | 7 days or until clinical improvement |
| Severe primary genital HSV | 5 mg/kg IV q8h | 5-7 days |
| VZV in severely immunocompromised | 10 mg/kg IV q8h | 7 days |
IV administration notes:
- Dilute to a concentration of ≤7 mg/mL before infusion
- Infuse slowly over 1 hour (not by bolus) to minimize renal toxicity
- Monitor BUN, creatinine, CBC
- CSF penetration is excellent (~50% of serum levels) - Harrison's 22E
Pediatric Dosing
| Indication | Dose |
|---|---|
| Neonatal HSV encephalitis | 20 mg/kg IV q8h (60 mg/kg/day) for minimum 21 days |
| Neonatal HSV - skin/eye/mouth | 20 mg/kg IV q8h x 14 days |
| Post-neonatal HSV CNS - oral suppression | 300 mg/m²/dose PO q8h x 6 months |
| Varicella in children <12 years | 20 mg/kg PO q6h (start within 24 h of onset) |
Neonatal HSV CNS disease is less responsive to acyclovir than adult HSV encephalitis, so higher weight-based dosing is used. - Harrison's 22E
Renal Dose Adjustment (Adults)
Acyclovir is renally excreted; dose must be reduced in renal impairment to prevent neurotoxicity and nephrotoxicity.
| CrCl | IV Dose Interval Adjustment |
|---|---|
| >50 mL/min | Normal dosing |
| 25-50 mL/min | q12h |
| 10-25 mL/min | q24h |
| <10 mL/min / hemodialysis | q24h; supplement after dialysis |
Dose adjustment is required in any patient with impaired renal glomerular filtration. Complications of therapy include elevated BUN/creatinine (5%), thrombocytopenia (6%), GI toxicity (7%), and neurotoxicity (1%). - Harrison's 22E, Goodman & Gilman's
Key Clinical Notes
- Topical acyclovir is much less effective than systemic therapy for genital HSV
- Acyclovir resistance is uncommon in immunocompetent patients, but can occur in immunocompromised hosts (mediated by changes in viral TK or DNA polymerase); treatment is foscarnet
- Bell's palsy: oral acyclovir in conjunction with corticosteroids appears beneficial
- CMV: acyclovir is ineffective for established CMV (use ganciclovir); ganciclovir is effective for CMV prophylaxis
- Varicella in children: aspirin should be avoided (Reye syndrome risk)
Sources: Harrison's Principles of Internal Medicine 22E (2025), Goodman & Gilman's Pharmacological Basis of Therapeutics, Adams & Victor's Principles of Neurology 12E; Drugs.com dosage guide for CDC recommendations
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