Tamiflu (Oseltamivir) Dosing and Treatment Guidelines
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 efficacy. 1, 2
Adults and Adolescents (≥13 years)
- Standard dose: 75 mg orally twice daily for 5 days 1, 2
- Treatment should ideally begin within 48 hours of symptom onset, though treatment after 48 hours may still provide benefit in patients with moderate-to-severe or progressive disease 1
Pediatric Patients (≥12 months)
Weight-based dosing for 5 days: 1, 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)
Age-based dosing for 5 days: 1, 2
- 9-11 months: 3.5 mg/kg per dose twice daily
- Term infants 0-8 months: 3 mg/kg per dose twice daily
- FDA approved down to 2 weeks of age 1
Preterm Infants
Postmenstrual age-based dosing (gestational age + chronological age): 1
- <38 weeks: 1.0 mg/kg twice daily for 5 days
- 38-40 weeks: 1.5 mg/kg twice daily for 5 days
- >40 weeks: 3.0 mg/kg twice daily for 5 days
Preterm infants require lower doses due to immature renal function and risk of drug accumulation 1
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. 1, 2
Adults and Adolescents (≥13 years)
- Post-exposure prophylaxis: 75 mg once daily for 10 days 1, 2
- Seasonal prophylaxis: 75 mg once daily for up to 6 weeks during community outbreak 1, 2
- Immunocompromised patients: May continue for up to 12 weeks 2
Pediatric Patients (≥1 year)
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)
- 3-11 months: 3 mg/kg once daily for 10 days 1
- <3 months: Not recommended unless situation judged critical due to limited safety data 1
Renal Impairment Adjustments
For patients with creatinine clearance 10-30 mL/min, reduce treatment dose to 75 mg once daily for 5 days. 1, 2
Treatment Dosing
- CrCl 10-30 mL/min: 75 mg once daily for 5 days 1
Prophylaxis Dosing
- CrCl 10-30 mL/min: Either 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses) 1
Formulation and Administration
Available Formulations
- Capsules: 30 mg, 45 mg, 75 mg 1, 2
- Oral suspension: 6 mg/mL when reconstituted (preferred for patients unable to swallow capsules) 1, 2
Suspension Dosing Volumes (6 mg/mL concentration)
Administration Tips
- Can be taken with or without food, though administration with meals may improve gastrointestinal tolerability and reduce nausea/vomiting 1, 2
- If commercial suspension unavailable, capsules can be opened and contents mixed with simple syrup or Ora-Sweet SF by retail pharmacies to achieve 6 mg/mL concentration 1
Clinical Efficacy Considerations
Timing of Treatment Initiation
Earlier treatment provides optimal clinical benefit—initiate within 48 hours of symptom onset whenever possible. 1
- Treatment within 36 hours reduces illness duration by 1.5 days and severity by up to 38% 1
- Treatment after 48 hours may still benefit patients with moderate-to-severe or progressive disease and should be strongly considered 1
- In critically ill patients, treatment within 5 days of symptom onset may improve survival 1
High-Risk Populations
Treatment should be offered to children with presumed serious, complicated, or progressive disease, irrespective of influenza immunization status. 1
- Children <2 years are at increased risk of hospitalization and complications 1
- Timely oseltamivir treatment reduces risks of complications, hospitalizations, and death 1
- Effective in elderly patients and those with chronic cardiac or respiratory disease 1
Special Populations
Pregnancy
- Same dosing as non-pregnant adults: 75 mg twice daily for 5 days 3
- Pregnancy substantially increases risk of severe influenza complications, and benefit-risk profile strongly favors treatment 3
- No causal relationship established between oseltamivir use and adverse pregnancy outcomes 3
Breastfeeding
- Breastfeeding mothers requiring antivirals should receive oseltamivir, and it is not a reason to discontinue breastfeeding 1, 3
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, 4
Adverse Effects
Common Side Effects
- Nausea and vomiting are the most common adverse effects, occurring in approximately 1 in 7 oseltamivir-treated patients compared to 1 in 12 placebo patients 1
- Gastrointestinal effects are typically mild and transient 1
- Other effects include headache and skin reactions 4
Mitigation Strategies
- Taking oseltamivir with food significantly reduces gastrointestinal adverse effects 1, 2
- Adverse effects rarely result in treatment discontinuation 1
Key Clinical Pitfalls to Avoid
Do not delay treatment waiting for laboratory confirmation in high-risk patients with suspected influenza—initiate empirically within 48 hours of symptom onset 1
Do not use standard term infant dosing in preterm infants—they require lower postmenstrual age-based dosing due to immature renal function 1
Do not withhold treatment beyond 48 hours in hospitalized or severely ill patients—treatment may still provide benefit in moderate-to-severe or progressive disease 1
Remember to adjust dosing in renal impairment—failure to do so may lead to drug accumulation and toxicity 1
Do not use prophylaxis as a substitute for vaccination—chemoprophylaxis is an adjunct, not a replacement for annual influenza immunization 1