BETHESDA, MD 26 December 2012—Previously available only under a special protocol, varicella zoster immune globulin is now an FDA-licensed product for reducing the severity of chickenpox in high-risk persons when given within 96 hours after exposure, the agency announced December 21.
High-risk persons, according to the product's labeling (PDF), include immunocompromised children and adults, newborns whose mothers had chickenpox shortly before or after delivery, premature infants, infants less than one year old, adults without evidence of immunity to the virus, and pregnant women.
In children, chickenpox is generally a self-limited disease of less than a week's duration. But the disease can be serious in persons at high risk for complications, according to the Centers for Disease Control and Prevention (CDC). Immunocompromised persons who get chickenpox are at risk for varicella zoster virus infection of the internal organs, which can lead to pneumonia, hepatitis, encephalitis, and disseminated intravascular coagulopathy. Pregnant women who get chickenpox are at increased risk for pneumonia. And fetuses exposed to the virus during the first half of their mothers' pregnancy are at risk of being born with congenital varicella syndrome, which can include abnormalities in the limbs, brain, and eyes.
The labeling for the immune globulin product, known as Varizig, recommends dosing it on the basis of the recipient's weight. There are six weight-based one-time doses, the lowest of which is 62.5 units for persons weighing 2 kg of less. This lowest dose differs from what CDC stated in 2006, when the agency announced the availability of Varizig for postexposure prophylaxis of chickenpox under an expanded access protocol. For persons weighing more than 2 kg, the recommended one-time dose remains 125 units per 10 kg of body weight, with a maximum dose of 625 units. The labeling has a table detailing the dose for each range of body weight and the number of 125-unit vials needed for that dose.
Each single-use vial of freeze-dried varicella zoster immune globulin is supplied in a carton that also contains a vial of sterile diluent. The product should be stored at 2–8 °C.
According to the labeling, the total volume of a dose should be divided and administered by i.m. injection in two sites. No injection should exceed 3 mL. Storage of the liquid immune globulin should not exceed 12 hours at 2–8 °C.
Injection-site pain and headache were the most commonly reported adverse events during the clinical studies of the immune globulin in high-risk persons, FDA said.
The labeling reports that adverse events related to the coagulation system occurred in 6 of the 372 patients who received the immune globulin through the expanded access protocol.
Varizig is manufactured by Cangene Corporation in Canada.