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.
Children younger than two years of age who are immunocompromised (e.g. those with severe combined immunodeficiency; those younger than two years of age who have undergone lung transplantation or hematopoietic stem cell transplantation) during the RSV season. Children with Down syndrome who have additional risk factors for lower respiratory tract infections such as congenital heart disease, chronic lung disease, or premature birth. Alaska Native and American Indian infants.Decisions regarding palivizumab prophylaxis for children in these groups should be made on a case-by-case basis. RSV Treatment
Because palivizumab is a passive antibody, it is ineffective in the treatment of RSV infection, and its administration is not recommended for this indication. A 2019 Cochrane review found no differences in palivizumab and placebo on outcomes of mortality, length of hospital stay, and adverse events in infants and children aged up to 3 years old with RSV. Larger RCTs will be required before palivizumab can be recommended as a treatment option. If an infant has an RSV infection despite the use of palivizumab during the RSV season, monthly doses of palivizumab may be discontinued for the rest of the RSV season due to the low risk of re-hospitalization. Current studies are in progress to determine new treatments for RSV rather than solely prophylaxis. Mechanism of Action
Palivizumab is a monoclonal antibody that targets the fusion (F) glycoprotein on the surface of RSV, and deactivates it. The F protein is a membrane protein responsible for fusing the virus with its target cell and is highly conserved among subgroups of RSV.