What are the recommended oseltamivir (Tamiflu) dosing regimens and durations for treatment in healthy adults and children, and for post‑exposure prophylaxis?

Oseltamivir (Tamiflu) Dosing and Duration

For adults and adolescents ≥13 years, the standard dose is 75 mg orally twice daily for 5 days for treatment, or 75 mg once daily for 10 days for post-exposure prophylaxis. 1, 2

Treatment Dosing

Adults and Adolescents (≥13 years)

• 75 mg orally twice daily for 5 days 1, 2
• Initiate within 48 hours of symptom onset for maximum benefit (earlier initiation within 12-24 hours provides even greater symptom reduction) 3, 4
• Take with or without food, though administration with meals reduces nausea and vomiting 1, 3, 4

Pediatric Patients (≥12 months, weight-based)

• ≤15 kg (≤33 lb): 30 mg twice daily for 5 days 1, 2
• >15-23 kg (>33-51 lb): 45 mg twice daily for 5 days 1, 2
• >23-40 kg (>51-88 lb): 60 mg twice daily for 5 days 1, 2
• >40 kg (>88 lb): 75 mg twice daily for 5 days 1, 2

Infants (<12 months, age-based)

• 9-11 months: 3.5 mg/kg per dose twice daily for 5 days 1, 3, 2
• Term infants 0-8 months: 3 mg/kg per dose twice daily for 5 days 1, 3, 2
• Preterm infants (postmenstrual age-based):
  • <38 weeks PMA: 1.0 mg/kg twice daily 1, 3
  • 38-40 weeks PMA: 1.5 mg/kg twice daily 1, 3

  • 40 weeks PMA: 3.0 mg/kg twice daily 1, 3

• Use lower doses for preterm infants due to immature renal function that can lead to toxic drug concentrations 1, 3

Prophylaxis Dosing

Adults and Adolescents (≥13 years)

• 75 mg orally once daily for 10 days following close contact with an infected individual 1, 5, 2
• May be extended up to 6 weeks during a community outbreak 2
• In immunocompromised patients, may continue for up to 12 weeks 2

Pediatric Patients (≥12 months, weight-based)

• Use the same weight-based doses as treatment, but once daily instead of twice daily for 10 days 1, 2
• ≤15 kg: 30 mg once daily 1, 2

• 15-23 kg: 45 mg once daily 1, 2

• 23-40 kg: 60 mg once daily 1, 2

• 40 kg: 75 mg once daily 1, 2

Infants (3-11 months)

• 3 mg/kg once daily for 10 days 1, 3
• Not recommended for infants <3 months unless the situation is judged critical due to limited safety and efficacy data 1, 3

Renal Impairment Adjustments

Dose adjustment is mandatory for patients with creatinine clearance <60 mL/min. 3

Treatment in Renal Impairment

• CrCl 10-30 mL/min: 75 mg once daily (instead of twice daily) for 5 days 1, 3

Prophylaxis in Renal Impairment

• CrCl 10-30 mL/min: 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses) 1, 3, 5

Formulation and Administration

Available Forms

• Capsules: 30 mg, 45 mg, and 75 mg 1, 3
• Oral suspension: 6 mg/mL when reconstituted (preferred for infants and children who cannot swallow capsules) 1, 2

Suspension Dosing Volumes (6 mg/mL concentration)

• 30 mg dose = 5 mL 1, 3
• 45 mg dose = 7.5 mL 1, 3
• 60 mg dose = 10 mL 1, 3
• 75 mg dose = 12.5 mL 1, 3

Administration Tips

• If commercial suspension is unavailable, pharmacies can compound a 6 mg/mL suspension based on package insert instructions 1, 3
• For infants, use a calibrated oral syringe (3-5 mL capacity) to measure small volumes accurately—do not use household spoons or the syringe supplied with the commercial product 3
• Capsules can be opened and contents mixed with liquid if swallowing is difficult 1, 5

Critical Timing Considerations

Treatment must be initiated within 48 hours of symptom onset for maximum effectiveness—earlier initiation (within 12-24 hours) provides even greater benefit, reducing illness duration by an additional 53.9-74.6 hours compared to starting at 48 hours. 3, 4

Complete the full 5-day treatment course even if symptoms improve earlier to ensure adequate viral suppression and prevent resistance development. 3

Common Pitfalls to Avoid

• Do not use weight-based categorical dosing (≤15 kg = 30 mg) for infants <12 months—use mg/kg dosing instead 3
• Do not apply term-infant dosing to preterm infants—use postmenstrual age-based dosing to avoid toxicity 1, 3
• Do not confuse prophylaxis dosing (once daily) with treatment dosing (twice daily)—this is a common prescribing error 5
• Do not delay prophylaxis waiting for laboratory confirmation in the index case—start based on clinical suspicion if within 48 hours of contact 5
• Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir, and do not use oseltamivir for 14 days after LAIV vaccination 3

Adverse Effects and Tolerability

• Nausea and vomiting occur in approximately 10% of adults and 14.3% of children, compared to 6% and 8.5% respectively with placebo 3, 4, 6
• Gastrointestinal effects are mild, transient, and typically resolve within 1-2 days 3, 4
• Taking oseltamivir with food significantly reduces the severity of nausea and vomiting 3, 4
• Only approximately 1% of patients discontinue therapy due to gastrointestinal side effects 3