What is the recommended dose of Oseltamivir (Tamiflu) for treating influenza?

Oseltamivir Dosing for Influenza Treatment

For adults and adolescents ≥13 years, administer oseltamivir 75 mg orally twice daily for 5 days; for children, use weight-based dosing ranging from 30-75 mg twice daily; and for infants, use age-specific mg/kg dosing. 1, 2

Adult and Adolescent Dosing (≥13 years)

• The standard treatment dose is 75 mg orally twice daily for 5 days 1, 3, 2
• Treatment should be initiated within 48 hours of symptom onset for maximum effectiveness 1, 4, 5
• Earlier initiation (within 12-24 hours) provides greater clinical benefit, reducing illness duration by an additional 53-74 hours compared to treatment started at 48 hours 5

Pediatric Dosing (1-12 years)

Weight-based dosing is recommended for children ≥1 year: 1, 3, 2

• ≤15 kg (≤33 lb): 30 mg twice daily for 5 days 1, 3, 2
• >15-23 kg (>33-51 lb): 45 mg twice daily for 5 days 1, 3, 2
• >23-40 kg (>51-88 lb): 60 mg twice daily for 5 days 1, 3, 2
• >40 kg (>88 lb): 75 mg twice daily for 5 days 1, 3, 2

Infant Dosing (<12 months)

Age-based mg/kg dosing is essential for infants: 1, 3, 6

• 9-11 months: 3.5 mg/kg per dose twice daily for 5 days 1, 3, 6
• Term infants 0-8 months: 3 mg/kg per dose twice daily for 5 days 1, 3, 6

Critical Caveat for Infants <3 months

• Infants <3 months show greater variability in drug exposure, requiring careful monitoring 6
• The 3 mg/kg dose still produces exposures within the target therapeutic range 6

Preterm Infant Dosing

Preterm infants require significantly lower doses based on postmenstrual age (PMA = gestational age + chronological age) due to immature renal function: 1, 3

• <38 weeks PMA: 1.0 mg/kg per dose twice daily 1, 3
• 38-40 weeks PMA: 1.5 mg/kg per dose twice daily 1, 3
• >40 weeks PMA: 3.0 mg/kg per dose twice daily 1, 3

This lower dosing prevents drug accumulation and toxicity in preterm infants with reduced renal clearance 3

Renal Impairment Dosing

For patients with creatinine clearance 10-30 mL/min: 1, 3

• Treatment: 75 mg once daily (not twice daily) for 5 days 1, 3
• Prophylaxis: 30 mg once daily OR 75 mg every other day for 10 days 1, 3

Dose adjustment is essential as oseltamivir is renally eliminated 1

Formulation and Administration

• Available as capsules (30 mg, 45 mg, 75 mg) and oral suspension (6 mg/mL when reconstituted) 1, 3, 2
• Administer with food to improve gastrointestinal tolerability and reduce nausea/vomiting 1, 3, 4, 5
• The oral suspension is preferred for patients who cannot swallow capsules 2

Oral Suspension Volumes (6 mg/mL concentration):

• 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

Common Pitfalls to Avoid

• Do not use adult dosing (75 mg) in children weighing <40 kg, as this may lead to excessive exposure 7
• Do not use standard pediatric weight-based dosing in preterm infants, as this causes drug accumulation and toxicity 1, 3
• Do not delay treatment beyond 48 hours of symptom onset, as efficacy diminishes significantly 1, 5
• Avoid administering live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir or within 14 days after oseltamivir, as the antiviral may reduce vaccine effectiveness 1

Adverse Effects

• Nausea and vomiting are the most common adverse events, occurring in approximately 10% of patients 4, 5, 8
• Gastrointestinal effects are typically mild, transient (1-2 days), and significantly reduced when taken with food 1, 4, 5
• Other adverse events include headache, diarrhea, and skin reactions 1