RSV Prophylaxis Dosing with Palivizumab
Palivizumab is administered at 15 mg/kg intramuscularly once monthly throughout the RSV season, with a maximum of 5 doses for most eligible infants. 1, 2
Standard Dosing Regimen
- Administer 15 mg/kg intramuscularly every 30 days during the RSV season 1, 3
- Maximum of 5 monthly doses provides protection for the typical RSV season (November through March/April in most U.S. regions) 1, 2
- The drug is packaged in single-dose vials at 50 mg/0.5 mL and 100 mg/1.0 mL without preservative 1
- Vials cannot be stored once opened, requiring vial-sharing schemes to minimize wastage 1
Modified Dosing for Specific Populations
Infants born 32-34 weeks gestation with risk factors receive a maximum of 3 doses (not 5), administered only during their first 90 days of life 1, 2, 4
Infants born before 29 weeks gestation receive up to 5 doses if younger than 12 months at RSV season start 2, 5, 4
Special Circumstances Requiring Additional Dosing
After cardiac bypass surgery, administer an additional 15 mg/kg dose as soon as the patient is medically stable 1, 5. This is critical because cardiopulmonary bypass reduces serum palivizumab concentrations by 58% (from mean 98 ± 52 mcg/mL to 41 ± 33 mcg/mL) 3
After extracorporeal membrane oxygenation (ECMO), administer an additional dose once the patient is stable 5, 4
Timing Considerations
- Begin prophylaxis in November for most U.S. regions, continuing monthly for 5 doses to provide protection through April 1
- In Florida, timing varies by region: Northwest Florida begins mid-November; north central and southwest Florida begin late September to early October; southeast Florida (Miami-Dade) begins in July 1
- For hospitalized infants, give the first dose 48-72 hours before discharge or promptly after discharge 2, 5
- If a monthly dose is due during hospitalization, administer on schedule 2
Pharmacokinetic Rationale
The 15 mg/kg monthly dosing achieves mean trough serum concentrations of 37 ± 21 mcg/mL after the first dose, increasing to 72 ± 50 mcg/mL after the fourth dose 3. These levels exceed the target concentration of 40 mcg/mL needed to reduce pulmonary RSV replication by >99% in animal models 3, 6
The elimination half-life is 24.5 days in pediatric patients, supporting monthly administration 3
Common Pitfalls to Avoid
Do not use only 3 doses for a 5-month season in standard-risk infants (those not in the 32-34 week gestation category). Population pharmacokinetic modeling demonstrates that 52% of infants would have subtherapeutic levels during month 4, and 85% during month 5, with only 3 doses 7
Do not discontinue prophylaxis if breakthrough RSV hospitalization occurs during the season—continue monthly doses as different RSV strains may cause reinfection 2
Do not administer more than 5 doses within the continental United States, as this provides >24 weeks of protective serum concentrations and is not cost-effective 1
Do not delay the post-bypass dose—the 58% reduction in serum levels leaves patients vulnerable to severe RSV infection 1, 5
Vaccine Compatibility
Palivizumab does not interfere with routine childhood immunizations—follow the standard vaccination schedule regardless of palivizumab use 1, 2, 5
Efficacy Data Supporting This Dosing
This 15 mg/kg monthly regimen for 5 doses reduced RSV hospitalizations by 55% overall in high-risk infants (10.6% placebo vs 4.8% palivizumab), with a 78% reduction in premature infants without chronic lung disease and 39% reduction in those with bronchopulmonary dysplasia 8
In infants with hemodynamically significant congenital heart disease, this regimen reduced RSV hospitalizations by 45% 1, 9