What is the recommended antiviral treatment for a patient with chicken pox (varicella), considering factors such as age, immune status, and disease severity?

Antiviral Treatment for Chickenpox

For immunocompromised patients with active chickenpox, intravenous acyclovir must be initiated immediately within 24 hours of rash onset, while healthy children generally do not require antiviral treatment unless they are at increased risk for moderate to severe disease. 1

Immunocompromised Patients

Intravenous acyclovir is the standard of care and must be started within 24 hours of rash onset to effectively reduce varicella-associated morbidity and mortality in high-risk populations. 1 This includes patients with:

• Primary and acquired immunodeficiency disorders 1
• Neoplastic diseases 1
• Those receiving immunosuppressive treatment (including corticosteroids ≥20 mg/day prednisolone or equivalent for ≥2 weeks, purine analogues, methotrexate, biologic and other advanced therapies) 2
• HIV-infected individuals who should be monitored closely and treated at earliest signs 1

The evidence demonstrates clear benefit when acyclovir is administered within the first 24 hours, with proven reduction in complications and death rates. 1

Healthy Children and Adolescents

Oral acyclovir (20 mg/kg per dose, 4 times daily for 5 days; maximum 800 mg per dose) should be considered for otherwise healthy persons at increased risk for moderate to severe varicella. 1, 3 This includes:

• Persons aged >12 years 1
• Those with chronic cutaneous or pulmonary disorders 1
• Patients receiving long-term salicylate therapy 1

Treatment must be initiated within 24 hours of rash onset to achieve clinical benefit, which includes decreased duration of new lesion formation, reduced fever duration, and decreased severity of symptoms. 1, 4 Five days of therapy is sufficient, as a 7-day course provides no additional benefit. 5

Important Caveat for Healthy Children

For otherwise healthy children under 12 years without risk factors, the clinical benefit of acyclovir is modest. 4 While treatment reduces lesion count (294 vs 347 lesions), limits fever duration to 3-4 days, and accelerates healing, it does not decrease transmission or reduce school absence duration. 6 The decision to treat should weigh these limited benefits against cost and inconvenience.

Pregnant Women

For pregnant women with serious varicella complications (particularly pneumonia), intravenous acyclovir should be considered. 6, 1 Acyclovir is FDA Category B, with animal studies showing no teratogenic effects. 6 A prospective registry of 596 first-trimester exposures showed birth defect rates approximating the general population, providing reassurance about safety. 1

Neonates and Premature Infants

For neonates whose mothers developed varicella from 5 days before to 2 days after delivery, Varicella-Zoster Immune Globulin (VariZIG) is indicated, not acyclovir. 6 VariZIG dosing is 125 units/10 kg body weight (maximum 625 units) administered intramuscularly. 6

For premature infants with postnatal exposure:

• Born at <28 weeks gestation or weighing <1,000g: VZIG indicated regardless of maternal immunity 6
• Born at ≥28 weeks gestation: VZIG indicated if mother lacks immunity 6

Post-Exposure Prophylaxis

Post-exposure varicella vaccination within 3 days of exposure is >90% effective in preventing disease and should be the first-line approach for healthy, susceptible individuals. 1 If given within 5 days, it remains 70% effective at preventing disease and 100% effective at modifying severe disease. 1

VariZIG should be administered within 96 hours (ideally as soon as possible) after exposure for high-risk individuals who cannot receive vaccination, including:

• Immunocompromised patients without evidence of immunity 6, 1
• Pregnant women without immunity 1
• Neonates and premature infants (as detailed above) 6, 1

Dosing: 125 units/10 kg body weight (maximum 625 units) intramuscularly. 6, 1

Patients receiving monthly high-dose IGIV (>400 mg/kg) within 3 weeks before exposure likely don't require VZIG. 6

Critical Prophylaxis Caveat

Acyclovir is NOT indicated for prophylactic use in healthy individuals after exposure—vaccination is the method of choice. 1 No studies support prophylactic acyclovir use in immunocompromised persons; VariZIG is recommended instead. 1 For immunocompromised patients on IBD therapies, current UK guidelines recommend a 7-day course of acyclovir starting 7 days after exposure rather than varicella immunoglobulin. 2

Special Populations: HIV-Infected Patients

For HIV-infected children aged 1-8 years with CD4 cell percentages ≥15%, varicella vaccination (not treatment) may be considered with 2 doses given 3 months apart. 2 For HIV-infected persons aged >8 years with CD4+ T-lymphocyte count >200 cells/µL, vaccination may also be considered (2 doses, 3 months apart). 2

If HIV-infected persons develop clinical varicella despite vaccination, acyclovir may modify disease severity. 2

Dosing Regimens

Oral Acyclovir (for eligible patients)

• Children 2 years and older: 20 mg/kg per dose, 4 times daily for 5 days (maximum 800 mg per dose) 3
• Adults and children >40 kg: 800 mg 4 times daily for 5 days 3

Intravenous Acyclovir (for immunocompromised patients)

• Dosing: 500 mg/m² or 10 mg/kg every 8 hours 7
• Duration: Continue until clinical improvement
• Monitoring: Maintain adequate hydration and urine flow, monitor mental status, adjust for renal impairment 7

Renal Dose Adjustment

For patients with creatinine clearance 0-10 mL/min/1.73 m²: 800 mg every 12 hours (instead of every 4 hours). 3 For hemodialysis patients, administer an additional dose after each dialysis. 3

Critical Safety Considerations

Avoid salicylates during and for 6 weeks after varicella due to Reye syndrome risk. 1 This is particularly important for patients on long-term salicylate therapy who are being considered for acyclovir treatment.

Monitor for bacterial superinfections (particularly invasive group A streptococcal infections), pneumonia, and neurologic complications, which are the leading causes of varicella-related deaths and require immediate intervention. 1 Neither acyclovir treatment nor vaccination has been shown to reduce these rare but serious complications in controlled trials. 4

Valacyclovir Alternative

Valacyclovir 20 mg/kg 3 times daily for 5 days (not to exceed 1 gram 3 times daily) is recommended for treatment of chickenpox in pediatric patients aged 2 to <18 years. 8 This provides equivalent systemic acyclovir exposure with less frequent dosing. However, valacyclovir is not recommended for children <2 years as efficacy and safety data are lacking. 8