What are the dosages for Oseltamivir (antiviral medication) in the treatment of influenza A?

Oseltamivir Dosages for Treatment of Influenza A

For the treatment of influenza A, oseltamivir (Tamiflu) should be administered at 75 mg twice daily for 5 days in adults, with weight-based dosing for children, starting within 48 hours of symptom onset for maximum efficacy. 1, 2

Adult Dosing

• Adults and adolescents ≥13 years: 75 mg twice daily for 5 days 1, 2
• Treatment should be initiated within 48 hours of symptom onset, with earlier initiation (within 12-24 hours) providing significantly greater benefit 3

Pediatric Dosing

Children ≥12 months (weight-based):

• ≤15 kg (≤33 lb): 30 mg twice daily for 5 days 1

• 15-23 kg (33-51 lb): 45 mg twice daily for 5 days 1

• 23-40 kg (51-88 lb): 60 mg twice daily for 5 days 1

• 40 kg (>88 lb): 75 mg twice daily for 5 days 1

Infants:

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

Preterm infants (based on postmenstrual age):

• <38 weeks postmenstrual age: 1.0 mg/kg twice daily 1
• 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily 1

• 40 weeks postmenstrual age: 3.0 mg/kg twice daily 1

• For extremely preterm infants (<28 weeks), consultation with a pediatric infectious diseases physician is recommended 1

Renal Dosage Adjustments

• Creatinine clearance 10-30 mL/min: 75 mg once daily for 5 days 1, 2
• Not recommended for patients with end-stage renal disease not undergoing dialysis 2

Administration Guidelines

• Oseltamivir can be taken with or without food, though administration with food may improve gastrointestinal tolerability 1, 2
• Available as capsules (30 mg, 45 mg, and 75 mg) and as powder for oral suspension (6 mg/mL) 1, 2
• For patients who cannot swallow capsules, the oral suspension is the preferred formulation 2

Clinical Pearls

• Timing is critical: Efficacy is highly dependent on early initiation of treatment. Starting within 12 hours of symptom onset can reduce illness duration by an additional 74.6 hours compared to starting at 48 hours 3
• The most common adverse effects are nausea and vomiting (approximately 10% of patients), which are typically mild, transient (resolving within 1-2 days), and can be minimized by taking with food 3
• Resistance to oseltamivir has been reported but remains relatively rare and appears to have limited clinical significance due to reduced transmissibility of resistant strains 3
• For children, weight-based dosing is preferred over age-based dosing when weight is known 1

Prophylaxis Dosing (for reference)

• Adults: 75 mg once daily for 10 days post-exposure or during community outbreaks 1, 2
• Children: Same weight-based dosing as treatment but administered once daily instead of twice daily 1, 2

Oseltamivir remains effective against most circulating influenza strains, including influenza A (H1N1) and A (H3N2) 1. Treatment should be initiated as soon as possible after symptom onset to maximize clinical benefit 3.