Oseltamivir (Tamiflu) Dosing for Influenza
For adults and adolescents ≥13 years, administer oseltamivir 75 mg orally twice daily for 5 days for treatment of influenza, initiated within 48 hours of symptom onset. 1, 2
Treatment Dosing by Age and Weight
Adults and Adolescents (≥13 years)
- 75 mg orally twice daily for 5 days 1, 3, 2
- Treatment should be initiated within 48 hours of symptom onset for maximum benefit 2, 4
- Earlier initiation (within 12 hours) reduces illness duration by an additional 3.1 days compared to treatment at 48 hours 4
Pediatric Patients (≥12 months)
Weight-based dosing twice daily for 5 days: 1, 3, 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
Infants (Birth to <12 months)
- 9-11 months: 3.5 mg/kg per dose twice daily for 5 days 1, 3
- Term infants 0-8 months: 3 mg/kg per dose twice daily for 5 days 1, 3, 2
Preterm Infants
Dosing based on postmenstrual age (gestational age + chronological age), twice daily for 5 days: 1, 3, 5
- <38 weeks postmenstrual age: 1.0 mg/kg per dose
- 38-40 weeks postmenstrual age: 1.5 mg/kg per dose
- >40 weeks postmenstrual age: 3.0 mg/kg per dose
The lower dosing for preterm infants is critical due to immature renal function and reduced drug clearance. 1, 5
Prophylaxis Dosing
Post-Exposure Prophylaxis (initiate within 48 hours of exposure)
Adults and Adolescents (≥13 years):
- 75 mg orally once daily for 10 days 1, 3, 2
- May extend up to 6 weeks during community outbreaks 2
- Immunocompromised patients may continue for up to 12 weeks 2
Pediatric Patients (≥1 year):
- Same weight-based doses as treatment, but once daily for 10 days 1, 3, 2
- May extend to 6 weeks during community outbreaks 2
Infants (3-11 months):
- 3 mg/kg once daily for 10 days 3, 5
- Prophylaxis is not recommended for infants <3 months unless the situation is critical, due to limited safety data 5
Renal Impairment Adjustments
For creatinine clearance 10-30 mL/min: 1, 3, 5, 2
- 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 Formulations
Suspension Dosing Volumes (6 mg/mL concentration)
- 30 mg dose = 5 mL 1, 3, 2
- 45 mg dose = 7.5 mL 1, 3, 2
- 60 mg dose = 10 mL 1, 3, 2
- 75 mg dose = 12.5 mL 1, 3, 2
Administration Tips
- Can be taken with or without food, but administration with meals improves gastrointestinal tolerability 1, 5, 2
- Capsules can be opened and mixed with liquid if patients cannot swallow them whole 5
- If commercial suspension is unavailable, pharmacies can compound it per package instructions 1, 5
Clinical Pearls and Common Pitfalls
Timing is Critical
The benefit of oseltamivir is time-dependent—treatment initiated within 12 hours of symptom onset provides 40% reduction in illness duration compared to 25-30% when started at 36 hours. 6, 4 Do not delay treatment while awaiting laboratory confirmation in symptomatic patients during influenza season.
Common Adverse Effects
- Nausea and vomiting occur in approximately 1 in 7 patients (versus 1 in 12 on placebo) 7
- These effects are typically transient, mild, and occur primarily with the first dose 8, 4
- Taking oseltamivir with food significantly reduces gastrointestinal symptoms 1, 2, 4
- Discontinuation rates are low (1.8%) 4
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 3, 5
Resistance Considerations
Lower doses or shorter treatment durations than approved may be ineffective and contribute to viral resistance emergence. 9 Always use the full 5-day treatment course.
Clinical Efficacy
Oseltamivir reduces illness duration by 1-1.5 days (25-30% reduction) and severity by up to 38% compared to placebo. 8, 7, 6 It also significantly reduces secondary complications, antibiotic use, and hastens return to normal activities. 8, 7