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, 3

Adults and Adolescents (≥13 years)

• 75 mg orally twice daily for 5 days 1, 2, 3
• Treatment should be initiated within 48 hours of symptom onset for maximum benefit, though treatment after 48 hours may still provide benefit in patients with moderate-to-severe or progressive disease 1, 4
• Earlier initiation provides progressively greater benefit—starting within 12 hours of fever onset can reduce illness duration by 3.1 days compared to starting at 48 hours 4

Pediatric Patients (≥12 months)

Weight-based dosing twice daily for 5 days: 1, 2, 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 (<12 months)

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

Preterm Infants

Dosing based on postmenstrual age (gestational age + chronological age) twice daily for 5 days: 2, 5

• <38 weeks: 1.0 mg/kg per dose
• 38-40 weeks: 1.5 mg/kg per dose
• >40 weeks: 3.0 mg/kg per dose

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Prophylaxis Dosing

For post-exposure prophylaxis, use the same weight-based doses as treatment but once daily instead of twice daily for 10 days. 1, 2, 3

Adults and Adolescents (≥13 years)

• 75 mg orally once daily for 10 days (post-exposure prophylaxis) 1, 2, 3
• May be extended up to 6 weeks during community outbreaks 3
• In immunocompromised patients, may continue up to 12 weeks 3

Pediatric Patients (≥1 year)

Use the same weight-based doses as treatment, but once daily for 10 days: 1, 2, 3

• ≤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 2, 3
• Not recommended for infants <3 months unless situation is judged critical due to limited safety 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, 5, 3

Treatment

• CrCl 10-30 mL/min: 75 mg once daily for 5 days 1, 2, 5

Prophylaxis

• CrCl 10-30 mL/min: 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses) 2, 5

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Formulation and Administration

Available Formulations

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

Suspension Dosing Volumes

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

Administration Tips

• Can be taken with or without food, though administration with meals improves gastrointestinal tolerability 1, 5, 3, 6
• If commercial suspension is 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, 5

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Clinical Efficacy Considerations

Treatment within 48 hours of symptom onset reduces illness duration by approximately 1-1.5 days in otherwise healthy adults, with greater benefit when started earlier. 6, 7, 4

• Oseltamivir reduces duration of fever, severity of symptoms, and time to return to normal activities 7, 4
• Treatment can reduce risks of complications including hospitalization and death, particularly in high-risk populations 1
• Treatment should still be offered to patients with severe, complicated, or progressive disease even if presenting >48 hours after symptom onset 1
• Efficacy is similar for both influenza A and B infections 7

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Important 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. 2, 5

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Common Adverse Effects

• Nausea and vomiting are the most common adverse effects (occurring in approximately 1 in 7 patients vs. 1 in 12 on placebo) 6, 7
• Gastrointestinal effects are typically mild, transient, and occur primarily with first dosing 6, 8, 4
• Taking oseltamivir with food significantly reduces nausea and vomiting 6, 8, 4
• Discontinuation rates are low (approximately 1.8%) 4