Aciclovir Dosing
For herpes simplex virus (HSV) infections, aciclovir dosing varies by disease severity and patient age: neonatal CNS/disseminated disease requires 20 mg/kg IV three times daily for 21 days, while non-neonatal CNS/disseminated disease requires 10 mg/kg IV three times daily for 21 days; for varicella-zoster virus (VZV) infections, use 10-15 mg/kg IV three times daily for encephalitis, or 800 mg orally five times daily for herpes zoster in immunocompetent adults. 1, 2, 3
HSV Infections
Neonatal Disease
- CNS or disseminated disease: 20 mg/kg IV three times daily for 21 days 4, 1, 4
- Skin, eye, or mouth disease: 20 mg/kg IV three times daily for 14 days 4, 1
- Critical caveat: Do not discontinue aciclovir in neonates with CNS disease until repeat CSF HSV DNA PCR is negative at days 19-21 of treatment 4, 1
Children (Outside Neonatal Period)
- CNS or disseminated disease: 10 mg/kg IV three times daily for 21 days 4, 1, 4
- Moderate-to-severe gingivostomatitis: 5-10 mg/kg IV three times daily, then switch to oral aciclovir when lesions regress; continue until complete healing 1
- Mild gingivostomatitis: 20 mg/kg oral (max 400 mg/dose) three times daily for 5-10 days 1
- Genital herpes (children <45 kg): 20 mg/kg oral (max 400 mg/dose) three times daily for 5-14 days 1
Adults and Adolescents
- Genital herpes (initial episode): 200 mg oral every 4 hours, 5 times daily for 10 days 3
- Genital herpes (recurrent): 200 mg oral every 4 hours, 5 times daily for 5 days 3
- Genital herpes (suppressive therapy): 400 mg oral twice daily for up to 12 months 3
- Alternative for mucocutaneous HSV: Valacyclovir 1 g oral twice daily (adults/adolescents only) 1
VZV Infections
Encephalitis
- Adults: 10-15 mg/kg IV three times daily for up to 14 days 2
Herpes Zoster (Shingles)
- Adults: 800 mg oral every 4 hours, 5 times daily for 7-10 days 3
- Immunocompromised patients: 10 mg/kg IV every 8 hours 5
Chickenpox (Varicella)
- Children ≥2 years and ≤40 kg: 20 mg/kg oral four times daily (80 mg/kg/day) for 5 days 3
- Children >40 kg and adults: 800 mg oral four times daily for 5 days 3
- Immunocompromised children: IV aciclovir is indicated; oral dosing may be considered at 800 mg five times daily 5, 6
Aciclovir-Resistant HSV
- Foscarnet: 40 mg/kg IV three times daily OR 60 mg/kg IV twice daily 4, 1
- Infuse slowly over 2 hours with saline fluid loading to minimize renal toxicity 4
Renal Impairment Adjustments
Dose modifications are mandatory for renal impairment 3:
For 200 mg every 4 hours regimen:
- CrCl >10 mL/min: 200 mg every 4 hours
- CrCl 0-10 mL/min: 200 mg every 12 hours
For 400 mg every 12 hours regimen:
- CrCl >10 mL/min: 400 mg every 12 hours
- CrCl 0-10 mL/min: 200 mg every 12 hours
For 800 mg every 4 hours regimen:
- CrCl >25 mL/min: 800 mg every 4 hours
- CrCl 10-25 mL/min: 800 mg every 8 hours
- CrCl 0-10 mL/min: 800 mg every 12 hours
Hemodialysis:
- Administer additional dose after each dialysis session 3
Critical Safety Considerations
Maintain adequate hydration throughout therapy to prevent crystalluria and obstructive nephropathy, which can affect up to 20% of patients, typically manifesting after 4 days of IV therapy 7, 3. Monitor renal function closely, especially with IV administration 4, 3.
Major toxicities include:
- Neutropenia (particularly in neonates receiving high-dose therapy: 46% in long-term suppressive therapy) 4
- Nephrotoxicity (6% Grade 3 or higher in neonates) 4
- Phlebitis, nausea, vomiting, rash 4
- Rare: hepatitis, bone marrow failure, encephalopathy 7
Avoid concomitant nephrotoxic agents as this increases risk of renal dysfunction and reversible CNS symptoms 3.
Prophylaxis Dosing
HSV Suppression:
- HIV-infected children with frequent recurrences (>3-6 episodes/year): Oral aciclovir 400 mg twice daily 8
- Post-neonatal HSV: 300 mg/m² body surface area 2-3 times daily 4
VZV Prophylaxis:
- Post-auto-HCT: 200 mg oral daily for up to 1 year reduces VZV disease incidence 9
Treatment Timing
Initiate therapy as early as possible for optimal outcomes 10, 7: