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, initiated within 48 hours of symptom onset for optimal efficacy. 1, 2

Adults and Adolescents (≥13 years)

• Standard dose: 75 mg orally twice daily for 5 days 1, 2
• 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
• Can be taken with or without food, though administration with meals may improve gastrointestinal tolerability 1, 2

Pediatric Patients (≥12 months)

Weight-based dosing 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)

• 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
• FDA approved for use in infants as young as 2 weeks of age 1, 2

Preterm Infants

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

• <38 weeks: 1.0 mg/kg twice daily for 5 days
• 38-40 weeks: 1.5 mg/kg twice daily for 5 days
• >40 weeks: 3.0 mg/kg twice daily for 5 days

The lower dosing for preterm infants is critical because immature renal function can lead to drug accumulation and toxicity if term infant doses are used 1

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Prophylaxis Dosing

For post-exposure prophylaxis, initiate oseltamivir within 48 hours of contact with an infected individual. 2

Adults and Adolescents (≥13 years)

• Standard dose: 75 mg orally once daily 1, 2
• Duration: 10 days for post-exposure prophylaxis; up to 6 weeks for seasonal prophylaxis during community outbreak 1, 2
• Immunocompromised patients: May continue for up to 12 weeks 2

Pediatric Patients (≥1 year)

Use same weight-based doses as treatment, but once daily instead of twice daily: 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
• Duration: 10 days post-exposure; up to 6 weeks during community outbreak 1, 2

Infants (3-11 months)

• 3-8 months: 3 mg/kg once daily for 10 days 1
• 9-11 months: 3.5 mg/kg once daily for 10 days 1
• <3 months: Not recommended 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, dose reduction is mandatory to prevent drug accumulation. 1, 2

Treatment Dosing in Renal Impairment

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

Prophylaxis Dosing in Renal Impairment

• CrCl 10-30 mL/min: Either 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses) 1, 2

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Formulations and Administration

Available Formulations

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

Suspension Dosing 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

Compounding Instructions

If commercially manufactured oral suspension is unavailable, capsules can be opened and contents mixed with simple syrup or Ora-Sweet SF (sugar-free) by retail pharmacies to achieve a final concentration of 6 mg/mL 1, 3

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Clinical Efficacy and Timing

Early treatment provides optimal clinical benefit—initiate within 48 hours of symptom onset whenever possible. 1, 2

Treatment Benefits

• Reduces duration of illness by 0.7-1.5 days in general populations 4, 5, 6
• Greater efficacy (1.5-2.0 days symptom reduction) when treatment initiated within 30 hours of symptom onset in febrile patients 6
• Reduces severity of illness by up to 38% compared with placebo 4
• Decreases incidence of secondary complications and antibiotic use 4

Late Treatment Considerations

Treatment initiated after 48 hours may still provide benefit in patients with moderate-to-severe disease, progressive disease, or those requiring ICU admission, and should be strongly considered 1, 7

High-Risk Populations

Treatment should be offered to children with presumed serious, complicated, or progressive disease, irrespective of influenza immunization status 1

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Special Populations

Pregnancy

Pregnant women should receive the same dosing as non-pregnant adults (75 mg twice daily for 5 days) throughout all trimesters and the postpartum period 8

Breastfeeding

Breastfeeding mothers requiring antivirals should receive oseltamivir, and it is not a reason to discontinue breastfeeding 1, 8

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Adverse Effects and Tolerability

The most common adverse effects are gastrointestinal—nausea and vomiting occur in approximately 5-15% of patients. 3, 4, 6

Common Adverse Effects

• Nausea and vomiting (mild and transient) 4, 6
• Headache 6
• Upper respiratory tract symptoms 6

Minimizing Adverse Effects

• Administer with food to reduce gastrointestinal symptoms 1, 3, 2
• Gastrointestinal effects rarely result in treatment discontinuation 5

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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. 8, 3

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Key Clinical Pearls

• Prophylaxis is not a substitute for vaccination but serves as an important adjunct during outbreaks 1
• Do not withhold treatment while awaiting laboratory confirmation in high-risk patients with suspected influenza 3
• Continue treatment despite negative initial tests unless an alternative diagnosis is established or clinical criteria suggest low probability of influenza 9
• Double-dose therapy (150 mg twice daily) confers no significant survival benefit and is not recommended 7
• Extended treatment beyond 5 days has limited supporting data except possibly in critically ill ICU patients with H1N1 infection 7