Tamiflu (Oseltamivir) Dosing
For adults and adolescents ≥13 years, the standard treatment dose is 75 mg orally twice daily for 5 days, and this should be initiated within 48 hours of symptom onset for maximum effectiveness. 1, 2
Adult and Adolescent Dosing (≥13 years)
Treatment: 75 mg orally twice daily for 5 days 1, 3, 2
Prophylaxis: 75 mg orally once daily 1, 3
- Duration: 10 days following close contact with infected individual, or up to 6 weeks during community outbreak 1, 2
- May extend to 12 weeks in immunocompromised patients 2
Pediatric Dosing (≥12 months to 12 years)
Weight-based treatment dosing (twice daily for 5 days): 1, 3, 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)
Prophylaxis dosing: Same weight-based doses given once daily for 10 days 1, 2
Infant Dosing (<12 months)
Treatment (twice daily for 5 days): 1, 3
- 9-11 months: 3.5 mg/kg per dose twice daily
- Term infants 0-8 months: 3.0 mg/kg per dose twice daily
Prophylaxis: 3.0 mg/kg once daily for 10 days (infants 3-11 months only) 1
- Prophylaxis not recommended for infants <3 months unless situation is critical due to limited safety data 1
Preterm Infant Dosing
Dosing based on postmenstrual age (gestational age + chronological age): 1, 3
- <38 weeks postmenstrual age: 1.0 mg/kg twice daily
- 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily
- >40 weeks postmenstrual age: 3.0 mg/kg twice daily
This lower dosing is essential due to immature renal function in preterm infants to avoid toxicity. 1
Renal Impairment Adjustments
For creatinine clearance 10-30 mL/min: 1, 3
- Treatment: 75 mg once daily (instead of twice daily) for 5 days
- Prophylaxis: 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses)
Dose adjustments are critical for patients with renal insufficiency to prevent drug accumulation. 1
Formulation and Administration
Available formulations: 1, 3, 2
- Capsules: 30 mg, 45 mg, 75 mg
- Oral suspension: 6 mg/mL when reconstituted (preferred for patients who cannot swallow capsules)
- Can be taken with or without food
- Taking with food significantly improves gastrointestinal tolerability and reduces nausea/vomiting, which occur in approximately 10-15% of patients 1, 4, 5
- Capsules can be opened and contents mixed with liquid if patient cannot swallow whole 1
- If commercial suspension unavailable, pharmacies can compound using capsule contents mixed with simple syrup or Ora-Sweet SF to achieve 6 mg/mL concentration 1
Critical Timing Considerations
Treatment must be initiated within 48 hours of symptom onset for maximum benefit. 1, 3, 2, 4
- Earlier initiation provides greater benefit: treatment within 12 hours reduces illness duration by an additional 74.6 hours compared to treatment at 48 hours 4
- Treatment within 24 hours reduces duration by an additional 53.9 hours compared to 48-hour initiation 4
- For high-risk patients, empiric treatment should be started without waiting for laboratory confirmation 1
Prophylaxis should be initiated within 48 hours following close contact with infected individual. 1
Drug Interactions
Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir use, and do not use oseltamivir for 14 days after LAIV vaccination. 1
Common Pitfalls to Avoid
- Do not delay treatment waiting for laboratory confirmation in high-risk patients 1
- Do not withhold oseltamivir due to mild illness or fever alone—these are not contraindications 1
- Remember to adjust dosing for renal impairment to prevent toxicity 1, 3
- For preterm infants, always calculate postmenstrual age (not just chronological age) to determine appropriate dosing 1, 3
- Oseltamivir is only effective during viral replication phase, making early initiation critical 4