Tamiflu (Oseltamivir) Dosing for Influenza
For adults and adolescents ≥13 years, the standard treatment dose is 75 mg orally twice daily for 5 days, and for prophylaxis, 75 mg once daily for 10 days post-exposure or up to 6 weeks during community outbreaks. 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 beyond 48 hours still provides substantial mortality reduction in hospitalized and high-risk patients 2, 4
- Earlier treatment is better: initiating within 12 hours reduces illness duration by 3.1 days more than starting at 48 hours 4
Pediatric Patients (≥12 months)
Weight-based dosing twice daily for 5 days: 1, 2, 5
- ≤15 kg: 30 mg (5 mL suspension) twice daily
- >15-23 kg: 45 mg (7.5 mL suspension) twice daily
- >23-40 kg: 60 mg (10 mL suspension) twice daily
- >40 kg: 75 mg (12.5 mL suspension) twice daily
Infants (Birth to <12 months)
The FDA has approved oseltamivir for infants as young as 2 weeks, and the AAP supports use from birth including preterm infants because benefits outweigh risks: 1, 2
- 9-11 months: 3.5 mg/kg per dose twice daily 1, 3
- 0-8 months (term): 3 mg/kg per dose twice daily 1, 3
- Preterm infants (dose by postmenstrual age): 1
- <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
Prophylaxis Dosing
Adults and Adolescents (≥13 years)
- 75 mg once daily for 10 days (post-exposure prophylaxis) 1, 2, 6
- 75 mg once daily for up to 6 weeks during community outbreaks 6, 3
- Initiate within 48 hours of exposure to infected individual 6
Pediatric Patients (≥1 year)
Use the same weight-based doses as treatment, but once daily instead of twice daily for 10 days: 1, 2, 6
- ≤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 if prophylaxis deemed necessary 2, 6
- Not recommended for infants <3 months unless situation judged critical due to limited safety data 1, 2
Renal Impairment Adjustments
For patients with creatinine clearance 10-30 mL/min: 1, 2, 5
- Treatment: 75 mg once daily for 5 days
- Prophylaxis: Either 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses)
Critical Timing Considerations
Do not delay treatment while awaiting laboratory confirmation in high-risk patients, as rapid antigen tests have poor sensitivity and treatment should begin immediately based on clinical suspicion. 2
Treatment after 48 hours still provides benefit, particularly in hospitalized and high-risk patients, and should be strongly considered for those with moderate-to-severe or progressive disease. 1, 2 One study of ICU patients with H1N1 suggested improved survival when oseltamivir was started within 5 days of symptom onset. 7
Special Populations
Pregnancy and Breastfeeding
- Pregnant women receive the same dosing as non-pregnant persons: 75 mg twice daily for 5 days 2
- Oseltamivir is preferred over zanamivir in pregnancy due to zanamivir's inhaled route 2
- Breastfeeding is not a contraindication to oseltamivir use 2
Immunocompromised Patients
- Should receive treatment regardless of time since symptom onset 2
- May require extended treatment duration beyond 5 days if illness is prolonged 2
- For prophylaxis, may continue up to 12 weeks during outbreaks 3
Formulation and Administration
- Available as capsules (30 mg, 45 mg, 75 mg) and oral suspension (6 mg/mL when reconstituted) 1, 2, 3
- May be taken with or without food, though administration with meals improves gastrointestinal tolerability 1, 3
- If commercial suspension unavailable, pharmacies can compound suspension from capsules to 6 mg/mL concentration 1
Common Pitfalls to Avoid
Do not confuse prophylaxis dosing (once daily) with treatment dosing (twice daily) - this is a frequent prescribing error. 6
Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir, and do not use oseltamivir for 14 days after LAIV vaccination as it may interfere with vaccine efficacy. 2, 6
Do not withhold treatment in high-risk or hospitalized patients presenting beyond 48 hours - these patients still derive substantial benefit, particularly regarding mortality reduction. 2
The most common adverse events are nausea and vomiting, which are transient, mild, and occur primarily with first dosing; taking oseltamivir with food significantly reduces these effects. 1, 8, 4