What is the recommended dosage of oseltamivir (Tamiflu) for treatment and prophylaxis of influenza?

Oseltamivir Dosing Recommendations

For adults and adolescents ≥13 years, administer oseltamivir 75 mg orally twice daily for 5 days for treatment and 75 mg once daily for prophylaxis, with treatment initiated within 48 hours of symptom onset for maximum efficacy. 1

Treatment Dosing

Adults and Adolescents (≥13 years)

• 75 mg orally twice daily for 5 days 2, 1
• Initiate within 48 hours of symptom onset; earlier initiation (within 12-24 hours) provides significantly greater clinical benefit 3
• Take with food to reduce gastrointestinal side effects 4, 1

Pediatric Patients (1-12 years) - Weight-Based Dosing

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

Infants (2 weeks to <1 year)

• 9-11 months: 3.5 mg/kg per dose twice daily for 5 days 4, 1
• Term infants 0-8 months: 3 mg/kg per dose twice daily for 5 days 2, 4, 1
• Infants <3 months: 3 mg/kg per dose twice daily for 5 days 2

Preterm Infants - Postmenstrual Age-Based Dosing

Preterm infants require substantially lower doses due to immature renal function and risk of drug accumulation 4, 5:

• <38 weeks postmenstrual age: 1.0 mg/kg twice daily 4, 5
• 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily 4, 5
• >40 weeks postmenstrual age: 3.0 mg/kg twice daily 4, 5

Prophylaxis Dosing

Adults and Adolescents (≥13 years)

• 75 mg orally once daily 2, 1
• Post-exposure prophylaxis: 10 days following close contact with infected individual 1
• Seasonal prophylaxis: up to 6 weeks during community outbreak 1
• Immunocompromised patients: up to 12 weeks 1

Pediatric Patients (1-12 years)

Use same weight-based doses as treatment but once daily instead of twice daily 2, 1:

• ≤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

• Duration: 10 days post-exposure or up to 6 weeks for seasonal prophylaxis 1

Infants (<1 year)

• Prophylaxis not recommended for infants <3 months unless situation judged critical due to limited safety data 2
• 3-11 months: 3 mg/kg once daily for 10 days 2

Renal Impairment Adjustments

Creatinine Clearance 10-30 mL/min

• Treatment: 75 mg once daily for 5 days (instead of twice daily) 4, 5, 1
• Prophylaxis: 30 mg once daily OR 75 mg every other day for 10 days 4, 5

Creatinine Clearance <10 mL/min

Dosing recommendations not established in FDA labeling; use with extreme caution 1

Formulation and Administration

Available Formulations

• Capsules: 30 mg, 45 mg, 75 mg 2, 1
• Oral suspension: 6 mg/mL when reconstituted 4, 1

Oral Suspension Volumes (6 mg/mL concentration)

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

Critical Clinical Pearls

Timing of Initiation

Treatment within 12 hours of symptom onset reduces illness duration by an additional 74.6 hours compared to initiation at 48 hours 3. Treatment within 24 hours provides an additional 53.9 hours of benefit 3. The 48-hour window is the outer limit, not the target 3.

Gastrointestinal Tolerability

Approximately 10% of patients experience transient nausea, vomiting, or diarrhea 4, 3. Administration with food significantly improves tolerability without affecting drug absorption 4, 1, 3.

Drug Interaction with Live Attenuated Influenza Vaccine (LAIV)

Avoid LAIV within 48 hours before oseltamivir use, and do not use oseltamivir for 14 days after LAIV vaccination to prevent interference with vaccine efficacy 4.

Common Pitfalls

• Do not use standard weight-based dosing for premature infants; postmenstrual age-based dosing is essential to avoid toxicity 2, 4
• Do not delay treatment waiting for laboratory confirmation of influenza; clinical diagnosis during influenza season is sufficient 3
• Ensure appropriate dosing devices for infants requiring small volumes (<5 mL) 1