What is the dosage and usage of Oseltamivir (Tamiflu) for treating and preventing influenza?

Oseltamivir (Tamiflu) Dosage and Usage for Treating and Preventing Influenza

Oseltamivir should be administered at 75 mg twice daily for 5 days in adults for treatment of influenza, with weight-based dosing for children, and should be initiated within 48 hours of symptom onset for maximum efficacy. 1, 2

Treatment Dosing Recommendations

Adults and Adolescents (≥13 years)

• 75 mg twice daily for 5 days 1, 2

Children (≥12 months)

• ≤15 kg (≤33 lb): 30 mg twice daily for 5 days 1, 3

• 15-23 kg (33-51 lb): 45 mg twice daily for 5 days 1, 3

• 23-40 kg (51-88 lb): 60 mg twice daily for 5 days 1, 3

• 40 kg (>88 lb): 75 mg twice daily for 5 days 1, 3

Infants

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

Preterm Infants

• <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

Prophylaxis Dosing Recommendations

Adults and Adolescents (≥13 years)

• 75 mg once daily for at least 10 days following exposure or up to 6 weeks during community outbreaks 4, 2

Children (≥1 year)

• ≤15 kg: 30 mg once daily for 10 days 3, 2

• 15-23 kg: 45 mg once daily for 10 days 3, 2

• 23-40 kg: 60 mg once daily for 10 days 3, 2

• 40 kg: 75 mg once daily for 10 days 3, 2

Infants (<1 year)

• 6-11 months: 25 mg once daily for 10 days 3
• 3-5 months: 20 mg once daily for 10 days 3
• ≤3 months: Not recommended unless situation judged critical 3

Special Populations

Renal Impairment

• For patients with creatinine clearance 10-30 mL/min:
  • Treatment: 75 mg once daily for 5 days 1, 3
  • Prophylaxis: 75 mg every other day for 10 days or 30 mg once daily for 10 days 1, 3

Administration Guidelines

• Oseltamivir can be taken with or without food, though administration with food may improve gastrointestinal tolerability 1, 5
• Available as capsules (30 mg, 45 mg, and 75 mg) and as powder for oral suspension (6 mg/mL) 2
• For oral suspension dosing: 30 mg = 5 mL, 45 mg = 7.5 mL, 60 mg = 10 mL, 75 mg = 12.5 mL 1, 2

Clinical Efficacy

• Treatment is most effective when initiated within 48 hours of symptom onset 6, 5
• Earlier initiation (within 12-24 hours) provides greater benefit, reducing illness duration by up to 74.6 additional hours compared to starting at 48 hours 5
• Oseltamivir reduces the duration of influenza symptoms by approximately 24-36 hours 7, 3
• Treatment also reduces the incidence of secondary complications such as otitis media, bronchitis, and pneumonia 6, 5

Common Side Effects

• Gastrointestinal effects, particularly nausea and vomiting (occurs in approximately 5-10% of patients) 3, 5
• Side effects are typically mild, transient, and resolve within 1-2 days 5

Important Considerations

• Not a substitute for annual influenza vaccination 2
• Effectiveness may vary based on influenza strain susceptibility patterns 2
• For institutional outbreaks, continue prophylaxis for a minimum of 2 weeks and up to 1 week after the end of the outbreak 3
• Resistance to oseltamivir has been reported but appears to be rare and of limited clinical significance 5

Oseltamivir remains an effective option for both treatment and prophylaxis of influenza A and B when used according to these guidelines, with the greatest benefit observed when treatment is initiated promptly after symptom onset.