Tamiflu (Oseltamivir) Dosing and Administration
For adults and adolescents ≥13 years, administer oseltamivir 75 mg orally twice daily for 5 days for treatment, or 75 mg once daily for 10 days for post-exposure prophylaxis. 1, 2, 3
Treatment Dosing
Adults and Adolescents (≥13 years)
- 75 mg orally twice daily for 5 days 1, 2, 3
- Initiate treatment within 48 hours of symptom onset for maximum benefit, though treatment after 48 hours may still provide benefit in patients with moderate-to-severe or progressive disease 1, 4
Pediatric Patients (≥12 months)
Weight-based dosing for 5 days, administered twice daily: 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 (<12 months)
- 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
Preterm Infants
Dosing based on postmenstrual age (gestational age + chronological age), twice daily for 5 days: 2, 4
- <38 weeks: 1.0 mg/kg per dose
- 38-40 weeks: 1.5 mg/kg per dose
- >40 weeks: 3.0 mg/kg per dose
Prophylaxis Dosing
Adults and Adolescents (≥13 years)
- 75 mg orally once daily for 10 days (post-exposure prophylaxis) 1, 2, 3
- May be extended up to 6 weeks during community outbreaks 3
- In immunocompromised patients, may continue up to 12 weeks 3
Pediatric Patients (≥1 year)
Use the same weight-based doses as treatment, but once daily instead of twice daily for 10 days: 1, 2
- ≤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)
- 3 mg/kg once daily for 10 days 2, 4
- Not recommended for infants <3 months unless situation is judged critical due to limited safety data 1
Renal Impairment Adjustments
For patients with creatinine clearance 10-30 mL/min: 1, 2, 4
- Treatment: 75 mg once daily for 5 days
- Prophylaxis: 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses)
Formulation and Administration
Available Forms
Suspension Dosing Volumes
Administration Tips
- Can be taken with or without food, though taking with meals improves gastrointestinal tolerability 1, 4, 3
- If commercial suspension unavailable, capsules can be opened and contents mixed with simple syrup or Ora-Sweet SF to achieve 6 mg/mL concentration 1, 4
Clinical Efficacy Considerations
Earlier treatment provides progressively better outcomes. Initiation within 12 hours of fever onset reduces illness duration by 3.1 days (41%) more than treatment started at 48 hours 5. However, treatment initiated after 48 hours in hospitalized patients with moderate-to-severe or progressive disease still provides benefit and should be strongly considered 1.
Timely oseltamivir treatment reduces risks of complications, hospitalizations, and death, particularly in high-risk populations including children <2 years, elderly patients, and those with chronic cardiac or respiratory disease 1, 6. Treatment duration may be extended beyond 5 days in critically ill patients, particularly those with H1N1 infection requiring ICU admission 7, 8.
Important 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 2, 4, as the antiviral may interfere with vaccine efficacy.
Common Adverse Effects
Nausea and vomiting are the most common adverse events, occurring in approximately 1 in 7 patients (versus 1 in 12 on placebo) 9, 6. These gastrointestinal effects are typically mild, transient, occur primarily with the first dose, and are significantly reduced when oseltamivir is taken with food 4, 9, 5. Discontinuation rates due to adverse events are low (1.8%) 5.