What is the prescribed dosage of Tamiflu (oseltamivir) for influenza (flu)?

Tamiflu (Oseltamivir) Prescribing for Influenza A

For adults and adolescents ≥13 years, prescribe oseltamivir 75 mg orally twice daily for 5 days, initiated within 48 hours of symptom onset for maximum effectiveness. 1, 2, 3

Treatment Dosing by Age Group

Adults and Adolescents (≥13 years)

• Standard dose: 75 mg orally twice daily for 5 days 1, 2, 4, 3
• Treatment must be initiated within 48 hours of symptom onset for optimal benefit 1, 2
• Earlier initiation (within 12-24 hours) provides progressively greater benefit, reducing illness duration by up to 3.1 days compared to treatment at 48 hours 5, 6

Pediatric Patients (≥12 months to 12 years)

Weight-based dosing twice daily for 5 days: 1, 2, 4, 3

• ≤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 (2 weeks to <12 months)

Age-based dosing twice daily for 5 days: 1, 2, 4

• 9-11 months: 3.5 mg/kg per dose twice daily
• Term infants 0-8 months: 3 mg/kg per dose twice daily

Preterm Infants

Postmenstrual age-based dosing (gestational age + chronological age) twice daily for 5 days: 1, 2, 4

• <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

Formulation and Administration

Available Formulations

• Capsules: 30 mg, 45 mg, and 75 mg 1, 2, 4, 3
• Oral suspension: 6 mg/mL when reconstituted (preferred for patients who cannot swallow capsules) 1, 2, 3

Suspension Dosing Volumes

1, 4

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

Administration Tips

• Can be taken with or without food, though taking with meals significantly improves gastrointestinal tolerability 1, 2, 3
• Capsules can be opened and mixed with liquid if patients cannot swallow them whole 1
• If commercial suspension unavailable, pharmacies can compound a suspension per package instructions 1

Renal Impairment Adjustments

For creatinine clearance 10-30 mL/min: 1, 2, 4

• Treatment dose: 75 mg once daily (instead of twice daily) for 5 days
• Prophylaxis dose: 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses)

Not recommended for end-stage renal disease patients not undergoing dialysis 3

Prophylaxis Dosing (Post-Exposure or Seasonal)

Adults and Adolescents (≥13 years)

• 75 mg once daily for at least 10 days (post-exposure) or up to 6 weeks (seasonal prophylaxis) 4, 3
• In immunocompromised patients, may continue up to 12 weeks 3

Pediatric Patients (≥1 year)

• Same weight-based doses as treatment, but once daily instead of twice daily for 10 days 4, 3
• Seasonal prophylaxis may extend up to 6 weeks 3

Infants (3-11 months)

• 3 mg/kg once daily for 10 days 4
• Prophylaxis not recommended for infants <3 months unless situation is critical due to limited safety data 1

Critical Timing Considerations

The 48-hour window is crucial: 1, 2, 5, 6

• Treatment initiated within 12 hours of fever onset reduces illness duration by 3.1 days (41% reduction) compared to treatment at 48 hours 5
• Treatment at 24 hours reduces illness by approximately 2 days (37-40% reduction) 6
• Benefits are progressive—every hour earlier provides incremental benefit 5

Common Adverse Effects and Management

Gastrointestinal effects are most common: 1

• Nausea and vomiting occur in approximately 1 in 7 patients (vs 1 in 12 on placebo) 7
• These effects are typically mild, transient, and occur primarily with first dosing 5
• Taking oseltamivir with food substantially reduces nausea and vomiting 1, 5
• Discontinuation due to adverse effects is rare (1.8%) 5

Important Drug Interactions

Live attenuated influenza vaccine (LAIV) interactions: 1, 4

• Avoid LAIV within 48 hours before starting oseltamivir
• Do not use oseltamivir for 14 days after LAIV vaccination (oseltamivir may inhibit vaccine virus replication)

Clinical Pearls

• Oseltamivir is active against both influenza A and B viruses 8, 7
• Treatment reduces illness duration by 1-1.5 days and severity by up to 38% when initiated promptly 8, 7
• Secondary complications and antibiotic use are significantly reduced in treated patients 8
• Oseltamivir is approved for use in children as young as 2 weeks of age 1
• Not a substitute for annual influenza vaccination—vaccination remains the primary prevention strategy 3