The most recent updates to these recommendations are based on new information regarding RSV seasonality, palivizumab pharmacokinetics, the incidence of bronchiolitis hospitalizations, the effect of gestational age and other risk factors on RSV hospitalization rates, the mortality of children hospitalized with RSV infection, the effect of prophylaxis on wheezing, and palivizumab-resistant RSV isolates. RSV Prophylaxis
All infants younger than one year who were born at <29 weeks (i.e. ≤28 weeks, 6 days) of gestation are recommended to use palivizumab. Infants younger than one year with bronchopulmonary dysplasia (i.e. who were born at <32 weeks gestation and required supplemental oxygen for the first 28 days after birth) and infants younger than two years with bronchopulmonary dysplasia who require medical therapy (e.g. supplemental oxygen, glucocorticoids, diuretics) within six months of the anticipated RSV season are recommended to use palivizumab as prophylaxis. A Cochrane review shows evidence that palivizumab RSV prophylaxis is effective at reducing the frequency of hospitalization in children with RSV infection.Since the risk of RSV decreases after the first year following birth, the use of palivizumab for children more than 12 months of age is generally not recommended with the exception of premature infants who need supplemental oxygen, bronchodilator therapy, or steroid therapy at the time of their second RSV season. RSV Prophylaxis Target Groups
Infants younger than one year of age with hemodynamically significant congenital heart disease. Infants younger than one year of age with neuromuscular disorders impairing the ability to clear secretions from the upper airways or pulmonary abnormalities.
Deactivating the F protein prevents the virus from fusing with its targets cell membrane and prevents the virus from entering the host cell. Pharmacodynamics
Palivizumab has demonstrated a significantly higher affinity and potency in neutralizing both A and B subtypes of RSV when compared with RSV-IGIV. Treatment with 2.5 mg/kg of palivizumab led to a serum concentration of 25-30 μg/mL in cotton rats and reduced RSV titers by 99% in their lungs. Pharmacokinetics
Absorption
A 2008 meta-analysis found that palivizumab absorption was quicker in the pediatric population compared to adults (ka = 1.01/day vs. ka = 0.373/day). The intramuscular bioavailability of this drug is approximately 70% in healthy young adults. Current recommendation for RSV immunoprophylaxis is administration of 5 x 15 mg/kg doses of palivizumab to maintain body concentrations above 40 μg/mL. Distribution
The volume of distribution is approximately 4.1 liters. Clearance
Palivizumab has a drug clearance (CL) of approximately 198 ml/day. The half-life of this drug is approximately 20 days with three doses sustaining body concentrations that will last the entire RSV season (5 to 6 months). A 2008 meta-analysis estimated clearance in the pediatric population by considering maturation of CL and body weight which showed a significant reduction compared to adults. Side effects
Palivizumab use may cause side effects, which include, but are not limited to:
Sore throat
Runny nose
Redness or irritation at the injection site
Vomiting
DiarrheaSome more serious side effects include:

Severe skin rash
Itching
Hives (urticaria)
Difficulty breathing

Contraindications
Contraindications for the use of palivizumab include hypersensitivity reactions upon exposure to palivizumab. Serious cases of anaphylaxis have been reported after exposure to palivizumab.