Oseltamivir (Tamiflu) Dosing for Children
For children ≥12 months, oseltamivir dosing is weight-based: 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, given for 5 days when treating influenza. 1, 2, 3
Weight-Based Dosing for Children ≥12 Months (Treatment)
The dosing is straightforward and based on current body weight 1, 2:
- ≤15 kg (≤33 lb): 30 mg twice daily for 5 days 1, 2, 3
- >15-23 kg (>33-51 lb): 45 mg twice daily for 5 days 1, 2, 3
- >23-40 kg (>51-88 lb): 60 mg twice daily for 5 days 1, 2, 3
- >40 kg (>88 lb): 75 mg twice daily for 5 days 1, 2, 3
Weight-based dosing is preferred over age-based dosing when weight is known, as it provides more accurate drug exposure 4.
Infant Dosing (<12 Months)
For infants under 1 year, dosing differs based on age 1, 2:
- 9-11 months: 3.5 mg/kg per dose twice daily for 5 days 1, 2, 4
- Term infants 0-8 months: 3 mg/kg per dose twice daily for 5 days 1, 2, 4
- Infants <3 months: 3 mg/kg per dose twice daily for 5 days 5
Oseltamivir is FDA-approved for infants as young as 2 weeks of age 1, 3, though it was not originally approved for children <1 year 5.
Preterm Infant Dosing
Preterm infants require substantially lower doses due to immature renal function 1, 4. Dosing is based on postmenstrual age (gestational age + chronological age) 1:
- <38 weeks postmenstrual age: 1.0 mg/kg twice daily 1, 2, 4
- 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily 1, 2, 4
- >40 weeks postmenstrual age: 3.0 mg/kg twice daily 1, 2, 4
For extremely preterm infants (<28 weeks), consultation with a pediatric infectious diseases specialist is recommended 4, as these infants have highly variable drug clearance and risk of toxicity 5.
Prophylaxis Dosing
For post-exposure or seasonal prophylaxis, use the same weight-based doses as treatment but give once daily instead of twice daily for 10 days 1, 2, 3:
- Children ≥12 months: Same weight-based doses as above, but once daily 1, 2
- Infants 3-11 months: 3 mg/kg once daily for 10 days 1, 2
- Prophylaxis is NOT recommended for infants <3 months unless the situation is judged critical due to limited safety data 5, 1
Formulation and Administration
Oseltamivir is available as 1, 3:
- Capsules: 30 mg, 45 mg, 75 mg
- Oral suspension: 6 mg/mL when reconstituted (preferred for children who cannot swallow capsules)
Suspension dosing volumes 1, 2:
- 30 mg dose = 5 mL
- 45 mg dose = 7.5 mL
- 60 mg dose = 10 mL
- 75 mg dose = 12.5 mL
Administration with food may improve gastrointestinal tolerability, as nausea and vomiting occur in approximately 5-15% of patients 1, 3.
Renal Impairment Adjustments
For children with creatinine clearance 10-30 mL/min 1, 2:
- Treatment: 75 mg once daily (instead of twice daily) for 5 days
- Prophylaxis: 30 mg once daily OR 75 mg every other day for 10 days
Critical Timing Considerations
Treatment should be initiated within 48 hours of symptom onset for maximum effectiveness 1, 4, reducing illness duration by approximately 1-1.5 days 6, 7. However, do not withhold treatment in high-risk or hospitalized patients even when presenting beyond 48 hours, as benefit still occurs 2.
Common Pitfalls to Avoid
- Do not use age-based dosing when weight is available – weight-based dosing is more accurate 4
- Do not use standard pediatric doses in preterm infants – they require postmenstrual age-based dosing to avoid toxicity 5, 1
- Do not delay treatment waiting for laboratory confirmation in high-risk patients, as rapid tests have poor sensitivity 2
- Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir, and do not use oseltamivir for 14 days after LAIV vaccination 1, 2