What is the recommended dosage of Tamiflu (Oseltamivir) for treating influenza?

Tamiflu (Oseltamivir) Dosage 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. 1, 2, 3

• For prophylaxis, the dose is 75 mg once daily for at least 10 days following exposure or up to 6 weeks during community outbreaks 1, 2, 3
• In immunocompromised patients, prophylaxis may be extended up to 12 weeks 2, 3

Pediatric Dosing (≥12 months to 12 years)

Weight-based dosing is essential for children, administered twice daily for 5 days for treatment or once daily for 10 days for prophylaxis: 1, 2

• ≤15 kg (≤33 lb): 30 mg twice daily (treatment) or 30 mg once daily (prophylaxis) 1, 2, 3
• >15-23 kg (>33-51 lb): 45 mg twice daily (treatment) or 45 mg once daily (prophylaxis) 1, 2, 3
• >23-40 kg (>51-88 lb): 60 mg twice daily (treatment) or 60 mg once daily (prophylaxis) 1, 2, 3
• >40 kg (>88 lb): 75 mg twice daily (treatment) or 75 mg once daily (prophylaxis) 1, 2, 3

Infant Dosing (<12 months)

For infants, age-based dosing using mg/kg calculations is required: 1, 2

• 9-11 months: 3.5 mg/kg per dose twice daily for 5 days (treatment) or 3 mg/kg once daily for 10 days (prophylaxis) 1, 2
• Term infants 0-8 months: 3 mg/kg per dose twice daily for 5 days (treatment) 1, 2, 3
• Infants 3-11 months: 3 mg/kg once daily for 10 days (prophylaxis) 1, 2

Critical Caveat for Infants <3 Months

Prophylaxis is not routinely recommended for infants younger than 3 months unless the situation is judged critical, due to limited safety data 1

Preterm Infant Dosing

Preterm infants require lower doses based on postmenstrual age (gestational age + chronological age) due to immature renal function: 1, 2

• <38 weeks postmenstrual age: 1.0 mg/kg twice daily 1, 2
• 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily 1, 2
• >40 weeks postmenstrual age: 3.0 mg/kg twice daily 1, 2

Renal Impairment Adjustments

For patients with creatinine clearance 10-30 mL/min, dose reduction is mandatory: 1, 2

• Treatment: 75 mg once daily (instead of twice daily) for 5 days 1, 2
• Prophylaxis: 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses) 1, 2

Oseltamivir is not recommended for patients with end-stage renal disease 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, 3

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 significantly improve gastrointestinal tolerability, as nausea and vomiting occur in approximately 5-15% of patients. 1, 2, 3

Capsules can be opened and mixed with liquid for patients unable to 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, 2, 4, 5

• Earlier initiation (within 24 hours) provides even greater benefit, reducing symptom duration by up to 40% 5
• However, treatment should not be withheld in high-risk or hospitalized patients 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

Immunocompromised patients should receive treatment regardless of time since symptom onset and may require extended treatment duration beyond 5 days if illness is prolonged. 2

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 use lower doses or shorter treatment durations than recommended, as this may contribute to viral resistance emergence 6
• Ensure proper dosing device for infants <1 year that can accurately measure small volumes 3
• Do not withhold treatment due to mild illness or fever alone in high-risk patients 1