What is the recommended dosage of Tamiflu (oseltamivir) for the treatment of influenza?

Oseltamivir (Tamiflu) Dosing for Influenza

For adults and adolescents ≥13 years, the standard treatment dose is 75 mg orally twice daily for 5 days, initiated within 48 hours of symptom onset. 1, 2, 3

Adult and Adolescent Dosing (≥13 years)

• Treatment: 75 mg orally twice daily for 5 days (equivalent to 12.5 mL of oral suspension twice daily) 1, 2, 3
• Prophylaxis: 75 mg orally once daily for at least 10 days following close contact with an infected individual, or up to 6 weeks during a community outbreak 1, 2, 3

Pediatric Dosing (≥12 months to 12 years)

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

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

Infant Dosing (<12 months)

Age-based dosing applies for infants, with treatment only (prophylaxis not recommended for <1 year): 1, 2

• 9-11 months: 3.5 mg/kg per dose twice daily for 5 days 1, 2
• Term infants 0-8 months: 3 mg/kg per dose twice daily for 5 days 1, 2, 3

Preterm Infant Dosing

Dosing for preterm infants is based on postmenstrual age (gestational age + chronological age) to avoid toxicity from immature renal function: 1, 2

• <38 weeks postmenstrual age: 1.0 mg/kg per dose twice daily for 5 days 1, 2
• 38-40 weeks postmenstrual age: 1.5 mg/kg per dose twice daily for 5 days 1, 2
• >40 weeks postmenstrual age: 3.0 mg/kg per dose twice daily for 5 days 1, 2

Renal Impairment Adjustments

Dose reduction is mandatory for patients with moderate to severe renal impairment: 1, 2, 3

• Creatinine clearance 10-30 mL/min (treatment): 75 mg once daily for 5 days 1, 2
• Creatinine clearance 10-30 mL/min (prophylaxis): 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses) 1, 2
• End-stage renal disease not on dialysis: Oseltamivir is not recommended 3

Formulation and Administration

• Available formulations: Capsules (30 mg, 45 mg, 75 mg) and oral suspension (6 mg/mL when reconstituted) 1, 2, 3
• Suspension dosing volumes: 30 mg = 5 mL, 45 mg = 7.5 mL, 60 mg = 10 mL, 75 mg = 12.5 mL 1, 2
• Administration with food improves gastrointestinal tolerability, as nausea and vomiting occur in approximately 5-15% of patients 1, 4, 5
• Capsules can be opened and mixed with liquid if patients cannot swallow them whole, or pharmacies can compound a suspension if the commercial product is unavailable 1

Critical Timing Considerations

• Initiate treatment within 48 hours of symptom onset for maximum benefit, reducing illness duration by 1-1.5 days in otherwise healthy patients 1, 2, 4, 6, 5
• Do not delay treatment while awaiting laboratory confirmation in high-risk patients, as rapid antigen tests have poor sensitivity 2
• Treatment beyond 48 hours still provides substantial benefit in hospitalized and high-risk patients, particularly for reducing mortality, though optimal benefit occurs with earlier initiation 2, 7

Special Populations

• Pregnant women: Use 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
• Immunocompromised patients: May require extended treatment duration beyond 5 days if illness is prolonged, and prophylaxis may be continued for up to 12 weeks 2, 3
• Elderly and high-risk patients with chronic cardiac/respiratory disease: Use standard adult dosing; oseltamivir significantly reduces acute febrile illness duration in these populations 6

Common Pitfalls to Avoid

• Do not withhold oseltamivir due to mild illness or fever alone in high-risk patients 1
• Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir, and do not use oseltamivir for 14 days after LAIV vaccination 1, 2
• Do not use double-dose oseltamivir (150 mg twice daily), as studies show no significant survival benefit compared to standard dosing 7
• Ensure accurate weight-based dosing in children using an appropriate oral dosing dispensing device that measures volume in mL 3