What are the weight‑based pediatric dosing guidelines for oseltamivir (Tamiflu) for treatment and post‑exposure prophylaxis, including age limits and renal impairment adjustments?

Pediatric Dosing for Oseltamivir (Tamiflu)

For children ≥12 months, use weight-based dosing: 30 mg twice daily for ≤15 kg, 45 mg twice daily for >15–23 kg, 60 mg twice daily for >23–40 kg, and 75 mg twice daily for >40 kg; for infants <12 months, use 3 mg/kg twice daily (0–8 months) or 3.5 mg/kg twice daily (9–11 months), with treatment duration of 5 days and prophylaxis given once daily for 10 days. 1, 2, 3

Weight-Based Dosing for Children ≥12 Months

For treatment (5 days, twice daily) and prophylaxis (10 days, once daily): 1, 3

• ≤15 kg: 30 mg per dose (5 mL of 6 mg/mL suspension)
• >15–23 kg: 45 mg per dose (7.5 mL of suspension)
• >23–40 kg: 60 mg per dose (10 mL of suspension)
• >40 kg: 75 mg per dose (12.5 mL of suspension)

The oral suspension (6 mg/mL concentration) is the preferred formulation for children who cannot swallow capsules. 3

Infant Dosing (<12 Months): Age and Weight-Based

Term Infants (≥37 weeks gestation at birth):

Treatment dosing (5 days, twice daily): 1, 2, 4

• 0–8 months: 3 mg/kg per dose twice daily
• 9–11 months: 3.5 mg/kg per dose twice daily

Prophylaxis dosing (10 days, once daily): 1, 2

• <3 months: NOT recommended unless situation judged critical due to limited safety data
• 3–8 months: 3 mg/kg once daily
• 9–11 months: 3.5 mg/kg once daily

Preterm Infants: Post-Menstrual Age-Based Dosing

Preterm infants require substantially lower doses based on post-menstrual age (gestational age + chronological age) due to immature renal function: 2, 4

• <38 weeks post-menstrual age: 1.0 mg/kg twice daily
• 38–40 weeks post-menstrual age: 1.5 mg/kg twice daily
• >40 weeks post-menstrual age: 3.0 mg/kg twice daily

For extremely preterm infants (<28 weeks post-menstrual age), consult a pediatric infectious disease specialist before initiating therapy. 4

Renal Impairment Adjustments

For creatinine clearance 10–30 mL/min: 1, 2

• Treatment: Reduce to once daily dosing (instead of twice daily) for 5 days
• Prophylaxis: Give half the standard once-daily dose daily, OR give the full once-daily dose every other day for 10 days (5 total doses)

Oseltamivir is not recommended for patients with end-stage renal disease not undergoing dialysis. 3

Administration and Timing

Initiate treatment within 48 hours of symptom onset for maximum benefit; starting within 12–24 hours provides substantially greater effectiveness. 4, 5 Early treatment (within 12 hours) reduces acute otitis media by 85% and shortens illness duration by 3.5 days in children with influenza A. 5

Administer with food to reduce gastrointestinal side effects (nausea, vomiting), which occur in approximately 10% of patients. 2, 4

Use a calibrated oral dosing syringe (3 mL or 5 mL) for accurate measurement in infants; household spoons must not be used. 4

Critical Pitfalls to Avoid

Never apply the weight-based categorical dosing (30 mg, 45 mg, 60 mg, 75 mg) to infants <12 months—these doses are designed only for children ≥12 months. 2, 4 Infants require mg/kg-based dosing.

Never use term infant dosing (3 mg/kg or 3.5 mg/kg) for preterm infants—they require post-menstrual age-based dosing to prevent drug accumulation and toxicity. 2, 4

Do not round up to the next weight category. A child weighing 15.2 kg receives 30 mg (not 45 mg), as they remain in the ≤15 kg bracket. 6

Do not stop therapy early even if symptoms improve—complete the full 5-day treatment course. 4

Do not confuse treatment dosing (twice daily) with prophylaxis dosing (once daily). 4

Do not delay antiviral therapy while awaiting laboratory confirmation during influenza season—clinical judgment is sufficient. 4

Special Populations and Considerations

The FDA has approved oseltamivir for treatment in children as young as 2 weeks of age, though it may be used from birth (including preterm infants) when benefits outweigh risks. 4, 3

For infants <1 year, particularly neonates and those with lower body weights, consult an infectious disease expert when considering antiviral therapy. 1

If commercial suspension is unavailable, pharmacies can compound a 6 mg/mL suspension by opening capsules and mixing contents with simple syrup or Ora-Sweet SF. 4

The duration of protection with prophylaxis lasts only as long as dosing continues; prophylaxis may be extended up to 6 weeks during community outbreaks or up to 12 weeks in immunocompromised patients. 3