SYNAGIS
Clinical safety rating
cautionComprehensive clinical and safety monograph for SYNAGIS (SYNAGIS).
Comprehensive clinical and safety monograph for SYNAGIS (SYNAGIS).
Prophylaxis of serious lower respiratory tract disease caused by respiratory syncytial virus (RSV) in pediatric patients with bronchopulmonary dysplasia (BPD), history of preterm birth (≤35 weeks gestational age), or hemodynamically significant congenital heart disease (CHD)
Palivizumab is a humanized monoclonal antibody that binds to the A antigenic site of the fusion (F) protein of respiratory syncytial virus (RSV), inhibiting viral entry into host cells by preventing fusion of the viral envelope with the host cell membrane.
| Metabolism | Palivizumab is a monoclonal antibody; it is degraded into small peptides and amino acids via catabolic pathways, similar to endogenous IgG. No specific metabolic enzymes are involved. |
| Excretion | Renal: minimal intact IgG recovered in urine; likely catabolized to peptides/amino acids. Fecal/biliary: not significantly eliminated. Main route: proteolytic catabolism. |
| Half-life | 18-27 days (terminal half-life in pediatric patients, mean ~21 days). Allows monthly dosing during RSV season. |
| Protein binding | ~98-99% bound, primarily to IgG receptors (FcRn) and endogenous IgG; binding to other serum proteins minimal. |
| Volume of Distribution | ~1.0-1.5 L/kg in infants; reflects distribution primarily within vascular space and extracellular fluid. |
| Bioavailability | IM: ~80-100% (nearly complete absorption after intramuscular injection). |
| Onset of Action | IM: Serum neutralizing titers peak by 48-72 hours but protective levels achieved within 1-2 days. |
| Duration of Action | ~1 month; requires monthly doses throughout RSV season due to half-life. |
| Molecular Weight | Approximately 150,000 Da |
15 mg/kg intramuscular once monthly during RSV season. Maximum dose: 300 mg (2 mL) per injection.
| Dosage form | VIAL |
| Renal impairment | No dose adjustment required for renal impairment. |
| Liver impairment | No dose adjustment required for hepatic impairment. |
| Pediatric use | Infants and children up to 24 months: 15 mg/kg intramuscular once monthly during RSV season. Maximum dose: 300 mg per injection. |
| Geriatric use | Not indicated for use in adults; no geriatric dosing data available. |
| 1st trimester | Palivizumab is a humanized monoclonal antibody (IgG1) that crosses the placenta in increasing amounts as pregnancy progresses. Available data from postmarketing use and case reports have not identified a drug-associated risk of major birth defects, miscarriage, or adverse maternal or fetal outcomes. However, use in the first trimester is not indicated as RSV season typically aligns with later stages of pregnancy. |
| 2nd trimester | No fetal harm observed in animal studies; however, human data are limited. Palivizumab is not indicated for use during pregnancy unless the benefit outweighs the risk, given the lack of robust human safety data. |
| 3rd trimester | In the third trimester, placental transfer is greatest due to active transport of IgG. No studies specifically evaluate palivizumab in pregnant women; however, given its high molecular weight, transfer is expected to be minimal until late gestation. Use only if clearly needed for RSV prophylaxis in the mother. |
Clinical note
Comprehensive clinical and safety monograph for SYNAGIS (SYNAGIS).
| Placental transfer | Palivizumab is an IgG monoclonal antibody that undergoes active placental transfer, increasing throughout pregnancy, especially in the third trimester. However, due to its high molecular weight (approx. 150,000 Da), transfer is relatively low compared to smaller molecules. No specific data on the extent of transfer in humans; animal studies suggest minimal fetal exposure. |
| Breastfeeding | Palivizumab is a large protein molecule (molecular weight ~150 kDa) that is unlikely to be excreted into human milk in significant amounts. Breastfeeding infants would have limited oral bioavailability due to digestion in the gastrointestinal tract. However, there are no controlled studies in breastfeeding women. Use with caution, weighing the benefits of RSV prophylaxis in the mother against potential risks to the infant. |
| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | Pregnancy Category B. Animal studies have not demonstrated fetal risk, but no adequate human studies in pregnant women. Palivizumab is a humanized monoclonal antibody (IgG1) that crosses the placenta, with increasing transfer in the second and third trimesters. No teratogenic effects have been reported. Use only if clearly needed. |
| Fetal Monitoring | No specific maternal or fetal monitoring required beyond standard obstetrical care. Monitor for signs of hypersensitivity reactions during and after administration. For preterm infants, monitor for respiratory syncytial virus (RSV) infection and adverse effects. |
| Fertility Effects | No studies on fertility effects in humans. Animal reproduction studies have not indicated impaired fertility. No known impact on male or female fertility. |
■ FDA Black Box Warning
None
| Serious Effects |
Severe hypersensitivity to palivizumab or any component of the formulationHistory of life-threatening allergic reactions to palivizumab
| Precautions | Anaphylaxis and hypersensitivity reactions (rare but severe), Coagulation disorders (thrombocytopenia) with bleeding complications in patients with CHD, Risk of infection transmission if administered with contaminated equipment, Not indicated for treatment of RSV disease, May interfere with RSV diagnostic tests |
| Food/Dietary | No known food interactions. Administer without regard to meals. |
| Clinical Pearls | Administer intramuscularly only, preferably in the anterolateral thigh; do not use if turbid or discolored; observe for 30 minutes post-injection for hypersensitivity; not for treatment of RSV disease; efficacy unproven in children with congenital heart disease other than hemodynamically significant conditions; may interfere with immune response to live vaccines; palivizumab is a monoclonal antibody, not a vaccine. |
| Patient Advice | This medication is given as a shot to prevent serious RSV lung infection; it does not treat existing infection. · Your child will receive injections monthly during RSV season (typically November through March). · Common side effects include fever, rash, and injection site reactions like redness or swelling. · Seek medical attention if your child develops signs of allergic reaction: hives, difficulty breathing, swelling of face/lips. · Inform healthcare provider about any bleeding disorders or recent vaccinations before receiving Synagis. |
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