Tamiflu (Oseltamivir) Dosing Recommendations
Adult and Adolescent Dosing (≥13 years)
For treatment of influenza, adults and adolescents should receive oseltamivir 75 mg orally twice daily for 5 days, initiated within 48 hours of symptom onset for maximum benefit. 1, 2
- For prophylaxis, the dose is 75 mg once daily for at least 10 days following close contact with an infected individual, or up to 6 weeks during a community outbreak 2, 3
- In immunocompromised patients, prophylaxis may be extended up to 12 weeks 3
Pediatric Dosing (≥12 months to 12 years)
Weight-based dosing is essential for children, with treatment given twice daily for 5 days: 1, 2
- ≤15 kg (≤33 lb): 30 mg twice daily
- >15-23 kg (>33-51 lb): 45 mg twice daily
- >23-40 kg (>51-88 lb): 60 mg twice daily
- >40 kg (>88 lb): 75 mg twice daily
For prophylaxis, use the same weight-based doses but once daily for 10 days 1, 2
Infant Dosing (<12 months)
Age-based dosing applies for infants, with treatment given twice daily for 5 days: 1, 2
- 9-11 months: 3.5 mg/kg per dose twice daily
- Term infants 0-8 months: 3 mg/kg per dose twice daily
- Prophylaxis (3-11 months): 3 mg/kg once daily for 10 days 2
Preterm Infant Considerations
Preterm infants require postmenstrual age-based dosing due to immature renal function: 1, 2
- <38 weeks postmenstrual age: 1.0 mg/kg twice daily
- 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily
- >40 weeks postmenstrual age: 3.0 mg/kg twice daily
Renal Impairment Adjustments
For patients 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 for 10 days OR 75 mg every other day for 10 days (5 total doses)
Oseltamivir is not recommended for end-stage renal disease patients not undergoing dialysis 3
Formulation and Administration
Oseltamivir is available as capsules (30 mg, 45 mg, 75 mg) and oral suspension (6 mg/mL when reconstituted): 1, 2
- Suspension dosing volumes: 30 mg = 5 mL, 45 mg = 7.5 mL, 60 mg = 10 mL, 75 mg = 12.5 mL 1
- Administration with food improves gastrointestinal tolerability, as nausea and vomiting occur in approximately 5-15% of patients 1, 3
- Capsules can be opened and mixed with liquid if patients cannot swallow them whole 1
Critical Timing Considerations
Treatment should be initiated within 48 hours of symptom onset for maximum effectiveness, reducing illness duration by 1-1.5 days in otherwise healthy patients. 1, 4, 5
- Earlier initiation provides greater benefit: treatment within 12 hours reduces illness duration by 3.1 days (41%) more than treatment at 48 hours 6
- However, treatment should not be withheld in high-risk or hospitalized patients even when presenting beyond 48 hours, as substantial mortality benefit still occurs 2
- Post-exposure prophylaxis should be initiated within 48 hours following close contact with an infected individual 1, 2
Special Populations
Pregnant women should receive the same dosing as non-pregnant adults (75 mg twice daily for 5 days), as pregnancy substantially increases the risk of severe influenza complications. 2
- Oseltamivir is preferred over zanamivir in pregnancy due to zanamivir's inhaled route 2
- Breastfeeding is not a contraindication to oseltamivir use 2
High-risk patients (elderly, chronic cardiac/respiratory disease, immunocompromised) should receive standard dosing and may require extended treatment duration beyond 5 days if illness is prolonged 2, 7
Drug Interactions
Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir administration, and do not use oseltamivir for 14 days after LAIV vaccination. 1, 2
Common Pitfalls to Avoid
- Do not delay treatment while waiting for laboratory confirmation in high-risk patients, as rapid antigen tests have poor sensitivity 2
- Do not withhold treatment due to mild illness or fever alone in high-risk populations 1
- Ensure proper dose adjustment for renal impairment to avoid toxicity 1, 2
- Use appropriate dosing devices for infants, particularly those requiring small volumes (<1 year) 3