Pediatric Antiviral
Aciclovir Dose System
Clinical Parameters
mL/min
Awaiting Data
Select indication and input patient parameters to generate aciclovir dosing.
Guidelines & Evidence
Verified
Last Review: 2026
When to Use
Primary Indications
Genital herpes (HSV-1 and HSV-2): initial, recurrent, and chronic suppression
Herpes simplex labialis (cold sores, fever blisters)
Herpes simplex virus encephalitis (IV, high-dose, life-threatening)
Herpes simplex keratitis (ophthalmic formulation, orphan designation)
Mucocutaneous HSV in immunocompromised hosts (transplant, HIV, chemotherapy)
Varicella-zoster virus (VZV): chickenpox (varicella) in immunocompetent and immunocompromised patients
Herpes zoster (shingles): acute treatment and prevention of postherpetic neuralgia
Neonatal herpes simplex virus infection (IV, 14-21 days, ophthalmologic involvement extends duration)
Eczema herpeticum (disseminated HSV in atopic dermatitis)
Herpes simplex meningitis (benign recurrent lymphocytic meningitis, Mollaret's meningitis)
Clinical Utility
Acyclovir is the antiviral drug of choice for most HSV and VZV infections due to its high selectivity for virus-infected cells. The drug requires activation by viral thymidine kinase (TK), which is present only in infected cells, conferring a 3,000-fold higher affinity for viral DNA polymerase versus host polymerase. This selectivity results in minimal host cell toxicity. Oral bioavailability is low (15-30%), necessitating frequent dosing (5 times daily for some indications). IV administration achieves therapeutic cerebrospinal fluid (CSF) levels (50% of plasma concentration), essential for encephalitis treatment. Resistance occurs primarily via TK-deficient mutants (most common in immunocompromised patients). Valacyclovir (prodrug with 3-5x higher bioavailability) and famciclovir are alternatives for immunocompetent patients requiring less frequent dosing.
Comparison with Other Antivirals
| Agent | Bioavailability (Oral) | Dosing Frequency | Activity Spectrum | Special Considerations | Resistance Pattern |
|---|---|---|---|---|---|
| Acyclovir | 15-30% | 3-5x daily | HSV-1, HSV-2, VZV, EBV (higher doses) | First-line, IV required for severe disease, nephrotoxic risk (crystalluria) | TK-deficient mutants (most common) |
| Valacyclovir (prodrug of acyclovir) | 54-67% (3-5x higher) | 2x daily (BID) | Same as acyclovir (converts in vivo) | Better compliance, more expensive, similar safety profile, TTP/HUS rare | Cross-resistance with acyclovir |
| Famciclovir (prodrug of penciclovir) | 77% | 2-3x daily | HSV-1, HSV-2, VZV, HBV | Longer intracellular half-life (10-20h vs 1h acyclovir), no IV formulation | Cross-resistance possible |
| Penciclovir (topical only) | N/A (topical) | q2h while awake | HSV-1, HSV-2 (topical labialis) | Topical only, cream 1% | TK-deficient resistance |
| Ganciclovir/Valganciclovir | 60% (valgan) | 2x daily (valgan) | CMV (100x more active than acyclovir), HSV/VZV (less active) | More myelosuppressive (neutropenia, thrombocytopenia), teratogenic | UL97 kinase mutations |
| Foscarnet | N/A (IV only) | q8h (IV infusion) | HSV (TK-resistant), CMV | Nephrotoxic (monitor Cr, calcium, phosphorus), genital ulceration | Active against TK-deficient mutants |
Last Comprehensive Review: 2026