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

How to Prescribe Tamiflu (Oseltamivir)

Treatment Dosing

For adults and adolescents ≥13 years, prescribe oseltamivir 75 mg orally twice daily for 5 days, initiated within 48 hours of symptom onset for maximum benefit. 1, 2

Adults and Adolescents (≥13 years)

• Standard dose: 75 mg orally twice daily for 5 days 1, 2, 3
• Initiate treatment within 48 hours of symptom onset for optimal efficacy, reducing illness duration by 1-1.5 days 1, 4
• Earlier initiation provides greater benefit—starting within 12 hours of fever onset reduces illness duration by 3.1 days compared to starting at 48 hours 5
• Do not withhold treatment in high-risk or hospitalized patients even if presenting beyond 48 hours 2

Pediatric Patients (≥12 months to 12 years)

Weight-based dosing twice daily for 5 days: 1, 2, 3

• ≤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

Infants (0-11 months)

Age-based dosing twice daily for 5 days: 1, 2, 6

• 9-11 months: 3.5 mg/kg per dose twice daily 1, 7
• Term infants 0-8 months: 3.0 mg/kg per dose twice daily 1, 6, 7

Preterm Infants

Postmenstrual age-based dosing (gestational age + chronological age) twice daily for 5 days: 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

Prophylaxis Dosing

Post-Exposure Prophylaxis

Initiate within 48 hours of close contact with an infected individual. 1, 2

Adults and adolescents ≥13 years: 1, 2, 3

• 75 mg once daily for 10 days

Pediatric patients (≥1 year to 12 years): 1, 2, 3

• Use same weight-based doses as treatment, but once daily for 10 days:
  • ≤15 kg: 30 mg once daily

  • 15-23 kg: 45 mg once daily

  • 23-40 kg: 60 mg once daily

  • 40 kg: 75 mg once daily

Infants 3-11 months: 1, 2

• 3 mg/kg once daily for 10 days
• Prophylaxis NOT recommended for infants <3 months unless situation is critical due to limited safety data 1

Seasonal Prophylaxis

• Same dosing as post-exposure prophylaxis, but continued for up to 6 weeks during community outbreak 2, 3
• In immunocompromised patients, may continue for up to 12 weeks 2, 3

Renal Impairment Adjustments

For 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 on dialysis. 1, 3

Formulation and Administration

Available Formulations

• Capsules: 30 mg, 45 mg, 75 mg 1, 2, 3
• Oral suspension: 6 mg/mL when reconstituted (preferred for patients who cannot swallow capsules) 1, 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 Tips

• Take with food to improve gastrointestinal tolerability—nausea and vomiting occur in approximately 5-15% of patients but are typically mild and transient 1, 4, 5
• Capsules can be opened and contents mixed with liquid if needed 1
• For infants <1 year, use an appropriate dosing device that accurately measures small volumes 3

Special Populations

Pregnancy and Breastfeeding

• Pregnant women receive the same dosing as non-pregnant adults: 75 mg twice daily for 5 days 2
• Pregnancy substantially increases risk of severe influenza complications, and benefit-risk profile strongly favors treatment 2
• Breastfeeding is NOT a contraindication to oseltamivir use 2

High-Risk Patients

Treat regardless of time since symptom onset in: 2

• Hospitalized patients
• Immunocompromised patients (may require extended treatment beyond 5 days if illness is prolonged)
• Patients with chronic cardiac or respiratory disease
• Elderly patients

Critical Timing Considerations

• Do NOT delay treatment while waiting for laboratory confirmation in high-risk patients—rapid antigen tests have poor sensitivity 2
• Maximum benefit occurs when treatment is initiated within 48 hours of symptom onset 1, 6, 5
• Treatment after 48 hours still provides substantial benefit in hospitalized and high-risk patients 2

Drug Interactions

Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir, and do not use oseltamivir for 14 days after LAIV vaccination. 1, 2

Common Pitfalls to Avoid

• Do not withhold treatment due to mild illness or fever alone—these are not contraindications 1
• Do not use standard adult dosing in infants—they require weight-based or age-based dosing due to immature renal function 1, 7
• Do not forget renal dose adjustments—failure to adjust can lead to toxicity 1
• Do not use prophylaxis in infants <3 months unless critical situation—limited safety data 1