Accidental Double Dose of RSV Immunoprophylaxis in a Newborn
Immediate Reassurance: No Harm Expected
An accidental second dose of RSV immunoprophylaxis (nirsevimab or palivizumab) in a newborn is not expected to cause significant harm and does not require specific treatment beyond observation. 1, 2
Expected Outcomes
Safety Profile Supports Minimal Risk
Nirsevimab has demonstrated a favorable safety profile with adverse events occurring in approximately 1.2% of recipients, with 97% of these being mild to moderate in intensity. 3
The incidence of serious adverse events with nirsevimab was not increased compared to placebo in clinical trials (6.8% vs 7.3%). 1, 4
No cases of anaphylaxis or immune-complex disease have been reported with nirsevimab in clinical trials. 3
The FDA label for nirsevimab states that in the event of overdose, there is no specific treatment required—the infant should simply be monitored for adverse reactions and provided symptomatic treatment as appropriate. 2
Specific Adverse Events to Monitor
Rash within 14 days occurred in 0.9% of nirsevimab recipients versus 0.6% with placebo. 3
Injection-site reactions within 7 days occurred in 0.3% of recipients versus 0% with placebo. 3
Antidrug antibodies were detected in 6.1% of nirsevimab recipients, though this did not correlate with increased adverse events. 4
Recommended Management
Immediate Actions
Monitor the infant for adverse reactions including hypersensitivity reactions, rash, and injection-site reactions over the next 14 days. 3, 2
Document the medication error in the medical record, including the dose, timing, and route of both administrations. 1
Provide symptomatic treatment if any adverse reactions develop (e.g., antipyretics for fever, local care for injection-site reactions). 2
No Additional Interventions Required
Do not attempt to reverse or counteract the extra dose—there is no antidote, and none is needed. 2
Do not administer additional doses during the current RSV season, as only a single dose of nirsevimab is recommended per season. 1
Continue routine childhood immunizations on schedule, as nirsevimab does not interfere with vaccine responses and can be safely coadministered. 1, 5
Key Clinical Context
Why Double Dosing Is Low Risk
Nirsevimab is a monoclonal antibody that is degraded into small peptides by normal catabolic pathways, not metabolized by cytochrome P450 enzymes or transporters. 2
The terminal half-life is approximately 71 days, meaning the body will naturally clear the excess antibody over time without intervention. 2
Clinical trials included infants receiving doses up to 200 mg (administered as two 100 mg injections for high-risk children 8-19 months), demonstrating safety at higher total doses. 3, 5
The dose-proportional pharmacokinetics suggest that doubling the dose would simply result in proportionally higher serum concentrations without unexpected toxicity. 2
Documentation and Follow-Up
Inform the parents about the medication error, reassure them about the expected safety, and provide clear instructions for monitoring. 1
Report the error through your institution's medication error reporting system to prevent future occurrences. 1
The infant does not require additional RSV prophylaxis for the remainder of the current RSV season, as a single dose provides protection for approximately 5 months (150 days). 1, 2
Common Pitfalls to Avoid
Do not panic or pursue aggressive interventions—the evidence strongly supports that accidental overdose is well-tolerated. 2
Do not withhold routine vaccines due to concern about interactions—nirsevimab can be safely coadministered with all routine childhood immunizations. 1, 5
Do not administer a third dose if the infant develops RSV infection despite prophylaxis—breakthrough infections can occur, and additional dosing is not indicated. 3
Do not confuse nirsevimab with palivizumab dosing schedules—nirsevimab requires only one dose per season, whereas palivizumab requires monthly dosing. 3, 6