Tamiflu (Oseltamivir) Dosing for Influenza
Treatment Dosing
For adults and adolescents ≥13 years, administer oseltamivir 75 mg orally twice daily for 5 days, initiated within 48 hours of symptom onset for optimal benefit. 1, 2
Adults and Adolescents (≥13 years)
- Standard dose: 75 mg twice daily for 5 days 1, 2
- Can be administered with or without food, though taking with meals improves gastrointestinal tolerability 2
- Treatment beyond 48 hours still provides substantial mortality benefit in hospitalized and high-risk patients 3
Pediatric Patients (≥12 months)
Weight-based dosing for 5 days: 1, 4, 2
- ≤15 kg (≤33 lb): 30 mg twice daily (5 mL oral suspension)
- >15-23 kg (>33-51 lb): 45 mg twice daily (7.5 mL oral suspension)
- >23-40 kg (>51-88 lb): 60 mg twice daily (10 mL oral suspension)
- >40 kg (>88 lb): 75 mg twice daily (12.5 mL oral suspension)
Infants (<12 months)
Age and weight-based dosing for 5 days: 1, 3
- 9-11 months: 3.5 mg/kg per dose twice daily
- Term infants 0-8 months: 3 mg/kg per dose twice daily
- Preterm infants (dosing by postmenstrual age): 1, 3
- <38 weeks: 1.0 mg/kg twice daily
- 38-40 weeks: 1.5 mg/kg twice daily
40 weeks: 3.0 mg/kg twice daily
Renal Impairment
For creatinine clearance 10-30 mL/min: 1, 3
- Treatment: 75 mg once daily for 5 days
- Adjust all pediatric doses similarly (reduce frequency to once daily)
Prophylaxis Dosing
For post-exposure prophylaxis, administer oseltamivir 75 mg once daily for 10 days in adults, initiated within 48 hours of exposure to an infected individual. 5, 2
Adults and Adolescents (≥13 years)
- Post-exposure prophylaxis: 75 mg once daily for 10 days 5, 2
- Seasonal/community outbreak prophylaxis: 75 mg once daily for up to 6 weeks 5, 2
- Immunocompromised patients: May continue up to 12 weeks 2
Pediatric Patients (≥1 year)
Same weight-based doses as treatment, but once daily for 10 days: 5, 4
- ≤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)
- 3-11 months: 3 mg/kg once daily for 10 days 3, 5
- <3 months: Not recommended unless situation judged critical due to limited safety data 1, 5
Renal Impairment (Prophylaxis)
For creatinine clearance 10-30 mL/min: 1, 5
- Option 1: 30 mg once daily for 10 days
- Option 2: 75 mg every other day for 10 days (5 total doses)
Critical Timing Considerations
Initiate treatment as soon as possible within 48 hours of symptom onset for maximum benefit—reducing illness duration by 1-1.5 days in otherwise healthy patients. 3, 6
- Earlier initiation (within 30 hours) provides even greater symptom reduction 7
- Do not withhold treatment in high-risk or hospitalized patients presenting beyond 48 hours, as treatment still significantly reduces mortality 3
- Treatment after 48 hours in ICU patients with H1N1 (up to 5 days post-symptom onset) may improve survival 8
- Do not delay treatment while awaiting laboratory confirmation in high-risk patients, as rapid antigen tests have poor sensitivity 1
Formulation and Administration
Oseltamivir is available as capsules (30 mg, 45 mg, 75 mg) and oral suspension (6 mg/mL when reconstituted). 1, 2
- Oral suspension is the preferred formulation for patients who cannot swallow capsules 2
- If commercial suspension unavailable, pharmacies can compound suspension from capsules to 6 mg/mL concentration 1
- Administer with food to reduce gastrointestinal side effects (nausea, vomiting) 2, 7
Special Populations
Pregnancy and Breastfeeding
Pregnant women should receive the same dosing as non-pregnant adults (75 mg twice daily for 5 days) throughout all trimesters and postpartum period. 3
- Pregnancy substantially increases risk of severe influenza complications 3
- Oseltamivir is preferred over zanamivir in pregnancy due to zanamivir's inhaled route 3
- Breastfeeding is not a contraindication to oseltamivir use 3
Immunocompromised Patients
- Treat regardless of time since symptom onset 3
- May require extended treatment duration beyond 5 days if illness is prolonged 3
- Prophylaxis may be continued up to 12 weeks during community outbreaks 2
Common Pitfalls to Avoid
Do not confuse prophylaxis dosing (once daily) with treatment dosing (twice daily)—this is a frequent prescribing error. 5
- Verify current weight in pediatric patients to avoid dosing errors 4
- Do not use oseltamivir within 48 hours before live attenuated influenza vaccine (LAIV) administration 3
- Do not use oseltamivir for 14 days after LAIV vaccination, as it may interfere with vaccine efficacy 3, 5
- Do not rely on negative rapid antigen tests to exclude influenza in high-risk patients—sensitivity is poor 1
Evidence for Efficacy
Reviews by CDC, WHO, and independent investigators consistently demonstrate that timely oseltamivir treatment reduces risks of complications, hospitalizations, and death. 1
- Reduces duration of illness by 1-1.5 days when started within 48 hours 3, 6
- Reduces severity of illness by up to 38% 9
- Significantly reduces incidence of secondary complications and antibiotic use 6
- Protective efficacy for prophylaxis ranges from 67-92% depending on population 6
- No benefit demonstrated with double-dose therapy 8