What is the recommended dosage and treatment duration for Tamiflu (oseltamivir) in the treatment and prevention of influenza?

Tamiflu (Oseltamivir) Dosing and Treatment Guidelines

Treatment Dosing

For adults and adolescents ≥13 years, administer oseltamivir 75 mg orally twice daily for 5 days, and for pediatric patients, use weight-based dosing with the same 5-day duration. 1, 2

Adults and Adolescents (≥13 years)

• 75 mg orally twice daily for 5 days 1, 2
• Can be taken with or without food, though administration with meals improves gastrointestinal tolerability 1
• Initiate treatment within 48 hours of symptom onset for optimal benefit, though treatment after 48 hours may still provide benefit in patients with moderate-to-severe or progressive disease 1, 3

Pediatric Patients (≥12 months)

Weight-based dosing twice daily 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 (2 weeks to <12 months)

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

Preterm Infants

Dosing based on postmenstrual age (gestational age + chronological age): 1

• <38 weeks: 1.0 mg/kg twice daily
• 38-40 weeks: 1.5 mg/kg twice daily
• >40 weeks: 3.0 mg/kg twice daily

Critical pitfall: Preterm infants require lower weight-based dosing due to immature renal function; using term infant doses can lead to drug toxicity. 1

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Prophylaxis Dosing

For post-exposure prophylaxis, administer oseltamivir at half the treatment dose (once daily instead of twice daily) for 10 days, initiated within 48 hours of exposure. 1, 2

Adults and Adolescents (≥13 years)

• 75 mg orally once daily for 10 days (post-exposure prophylaxis) 1, 2
• For seasonal prophylaxis during community outbreak: up to 6 weeks 2
• In immunocompromised patients: may continue up to 12 weeks 2

Pediatric Patients (≥1 year)

Same weight-based doses as treatment, but once 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 mg/kg once daily for 10 days 1
• Not recommended for infants <3 months unless situation judged critical due to limited safety and efficacy data 1

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Renal Impairment Adjustments

For patients with creatinine clearance 10-30 mL/min, reduce the dose to 75 mg once daily for treatment and 30 mg once daily (or 75 mg every other day) for prophylaxis. 1, 2

Treatment

• 75 mg once daily for 5 days 1

Prophylaxis

• 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses) 1

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Formulation and Administration

Available Forms

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

Suspension Dosing Volumes

• 30 mg dose = 5 mL
• 45 mg dose = 7.5 mL
• 60 mg dose = 10 mL
• 75 mg dose = 12.5 mL 1, 2

Compounding Alternative

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

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Timing and Clinical Efficacy

Earlier treatment initiation provides progressively greater benefit—starting within 12 hours of symptom onset reduces illness duration by 3.1 days more than starting at 48 hours. 3

• Treatment within 48 hours is standard recommendation, but benefits are seen at every time point of intervention 1, 3
• For hospitalized patients with moderate-to-severe or progressive disease, treatment beyond 48 hours should be strongly considered 1
• In critically ill ICU patients with H1N1, oseltamivir may improve survival when initiated within 5 days of symptom onset 4
• Treatment duration may be extended beyond 5 days in critically ill patients, though data are limited 5, 4

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Safety and Tolerability

The most common adverse effects are nausea and vomiting (occurring in approximately 1 in 7 patients), which are transient and can be minimized by taking oseltamivir with food. 1, 6, 7

• Gastrointestinal effects are mild and rarely lead to discontinuation (1.8% discontinuation rate) 6, 3
• Other adverse effects include headache and skin reactions 8

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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. 9, 8

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Evidence for Efficacy

Multiple CDC, WHO, and independent reviews have consistently found that timely oseltamivir treatment reduces risks of complications, hospitalizations, and death, particularly in high-risk populations including children <2 years, elderly, and those with chronic cardiac or respiratory disease. 1, 7

• Reduces illness duration by 19-41% depending on timing of initiation 7, 3
• Reduces secondary complications and antibiotic use 6, 7
• Effective against both influenza A and B 7
• Prophylaxis provides >70% protection in unvaccinated adults and 92% in vaccinated high-risk elderly 6