Beyfortus
Beyfortus
Generic Name
Beyfortus
Mechanism
- Target: Fusion (F) protein on the RSV surface.
- Binding: Nirsevimab binds with high affinity to a pre‑fusogenic epitope on the F protein.
- Neutralization: Inhibits membrane fusion and viral entry into host cells, preventing replication.
- Half‑life extension: Fc engineering (LS mutation) prolongs systemic exposure (~40 days).
Pharmacokinetics
| Parameter | Typical Value |
| Absorption | Rapid subcutaneous uptake; peak serum T12‑24 h |
| Distribution | Primarily intravascular; limited tissue penetration |
| Metabolism | Proteolytic catabolism to amino acids (IgG catabolism pathway) |
| Elimination | Renal clearance minimal; largely via proteases |
| Half‑life | ~45 days (personalized by body weight) |
| Steady state | Achieved after 1‑2 monthly doses |
• Weight‑based dosing (160 mg for < 20 kg; 300 mg for ≥ 20 kg).
• No clinically relevant drug‑drug interactions.
Indications
- Prophylaxis of RSV lower respiratory tract disease (bronchiolitis, pneumonia) in:
- Infants ≤12 months at high risk (prematurity, chronic lung disease, congenital heart disease).
- Children 12–59 months with risk factors (congenital heart disease, chronic pulmonary disease, post‑transplant).
- Seasonal use during RSV peaks (fall–winter in temperate climates, year‑round in tropics).
Contraindications
- Contraindicated:
- Known hypersensitivity to nirsevimab or any excipient.
- Warnings/Precautions:
- Hypersensitivity reactions (anaphylaxis). Monitor 30 min post‑dose.
- Use in patients with immunoglobulin deficiencies may reduce efficacy.
- No clear data on live vaccine interaction; administer HSV vaccine at least 2 weeks before or after.
Dosing
- Route: Subcutaneous injection.
- Dose:
- Weight 6 weeks.
- Technique:
- Use 23‑g or 24‑g needle; inject into abdomen or thigh.
- Employ ice‑pack if pain or swelling occurs.
- Storage: 2–8 °C; protect from light.
Monitoring
- Baseline: Weight, serum bilirubin (if cholestasis), immunoglobulin levels in high‑risk infants.
- Post‑dose: Observe for 30 min for hypersensitivity; document injection‑site reaction.
- During season: Monitor for respiratory symptoms; document any RSV PCR testing.
- Safety follow‑up: Visite at 4 weeks post‑dose for weight assessment and injection‑site evaluation.
Clinical Pearls
- Weight‑adapted dosing ensures therapeutic exposure across neonates and toddlers; avoid fixed dosing.
- Broad‑era coverage: With a 45‑day half‑life, a single dose protects across an entire RSV season, simplifying adherence.
- Immunologic advantage: Unlike ribavirin, Beyfortus does not require respiratory therapist‑shielded rooms or aerosol delivery.
- Elderly and comorbid: Although not FDA‑approved for ≥ 5 years, growing data suggest efficacy in older children with heart disease; discuss with cardiology.
- Travel‑accompanying infants: If traveling during RSV season, they often require a second dose; coordinate with travel medicine.
- Pharmacokinetic nuances: In infants < 3 months, the volume of distribution is lower; hence the 160 mg dose maximizes serum levels while minimizing under‑dosing risk.
- Adverse event reporting: Report any severe reactions to the Vaccine Adverse Event Reporting System (VAERS) for pharmacovigilance.
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• *Data compiled from FDA prescribing information, EMA guidelines, and peer‑reviewed pharmacology texts. Use in clinical practice after confirming local regulatory approvals.*