What is the recommended dose of Varicella (chickenpox) immunoglobulin?

Varicella Immunoglobulin Dosing

The recommended dose of varicella zoster immune globulin (VariZIG) is 125 IU per 10 kg of body weight, administered intramuscularly, up to a maximum of 625 IU (five vials). 1

Weight-Based Dosing Algorithm

Minimum doses for small patients:

• Patients weighing ≤2.0 kg: 62.5 IU (0.5 vial) 1
• Patients weighing 2.1–10.0 kg: 125 IU (one vial) 1
• Patients >10 kg: 125 IU per 10 kg body weight, capped at 625 IU total 1

Administration Details

Route and preparation:

• VariZIG is supplied in 125-IU vials and must be administered intramuscularly as directed by the manufacturer 1
• The product should be injected directly into the deltoid or gluteal muscle using an appropriate needle length for the patient's age and size 2

Critical timing considerations:

• Administer as soon as possible after varicella exposure, ideally within 96 hours, but can be given up to 10 days post-exposure 1
• Evidence from expanded-access programs demonstrates comparable efficacy when administered ≤96 hours versus >96 hours (up to 10 days), with varicella incidence of 6.2% versus 9.4% respectively 3
• The extended 10-day window is based on international data showing comparable disease attenuation even when given 4-10 days post-exposure 1

High-Risk Populations Requiring VariZIG

Specific patient groups who should receive prophylaxis: 1

• Immunocompromised patients without evidence of immunity
• Newborn infants whose mothers developed varicella 5 days before to 2 days after delivery
• Hospitalized premature infants ≥28 weeks gestation whose mothers lack immunity to varicella
• Hospitalized premature infants <28 weeks gestation or weighing ≤1,000 g at birth, regardless of maternal immunity status
• Pregnant women without evidence of immunity

Important Clinical Caveats

Patients who do NOT need VariZIG:

• Individuals with verified positive varicella IgG levels (except bone marrow transplant recipients) are considered immune and do not require prophylaxis 4, 5
• Patients receiving monthly high-dose IGIV (>400 mg/kg) are likely protected if the last dose was within 3 weeks of exposure 4

Repeat dosing:

• For high-risk patients with additional varicella exposures ≥3 weeks after initial VariZIG administration, another dose should be considered 1

Post-administration monitoring:

• Observe patients closely for 28 days after exposure (extended from the typical 21-day incubation period due to potential prolongation by immune globulin) 1
• Institute antiviral therapy immediately if signs or symptoms of varicella develop 1

Vaccine timing:

• Delay varicella vaccination for ≥5 months after VariZIG administration to avoid interference with vaccine response 1

Safety Profile

Common adverse reactions:

• Pain at injection site (2%) and headache (2%) are the most frequent side effects 1

Absolute contraindications: 1

• History of anaphylactic or severe systemic reactions to human immune globulins
• IgA-deficient patients with antibodies against IgA and history of hypersensitivity

Pregnancy and lactation are not contraindications 2