Recommended Treatment Regimen for Influenza Using Oseltamivir
The recommended treatment regimen for influenza using oseltamivir is 75 mg twice daily for 5 days in adults, with weight-based dosing for children, and should be initiated within 48 hours of symptom onset for maximum effectiveness. 1, 2, 3
Adult Dosing
- Adults and adolescents (≥13 years) should receive 75 mg of oseltamivir twice daily for 5 days 1, 2, 3
- Oseltamivir can be taken with or without food, though administration with food may improve gastrointestinal tolerability 1, 2, 4
- For prophylaxis, adults should receive 75 mg once daily for 10 days following exposure to an infected individual 1, 2
Pediatric Dosing
For children ≥12 months, weight-based dosing is recommended 1, 2, 3:
- ≤15 kg (≤33 lb): 30 mg twice daily for 5 days
15-23 kg (33-51 lb): 45 mg twice daily for 5 days
23-40 kg (51-88 lb): 60 mg twice daily for 5 days
40 kg (>88 lb): 75 mg twice daily for 5 days
For infants 9-11 months: 3.5 mg/kg per dose twice daily for 5 days 1, 2
For term infants 0-8 months: 3 mg/kg per dose twice daily for 5 days 1, 2
Preterm Infant Dosing
- Preterm infants require lower dosing based on postmenstrual age 1, 4:
- <38 weeks postmenstrual age: 1.0 mg/kg per dose twice daily
- 38-40 weeks postmenstrual age: 1.5 mg/kg per dose twice daily
40 weeks postmenstrual age: 3.0 mg/kg per dose twice daily
Dosing in Renal Impairment
- For patients with creatinine clearance 10-30 mL/min 1, 4:
- Treatment: 75 mg once daily for 5 days
- Prophylaxis: 30 mg once daily for 10 days or 75 mg once every other day for 10 days (5 doses)
Timing of Treatment
- Treatment should be initiated within 48 hours of symptom onset for maximum effectiveness 5
- Earlier initiation provides greater benefit - treatment within 12 hours after symptom onset reduces illness duration by an additional 74.6 hours compared to starting at 48 hours 5
- Treatment may still be beneficial when started within 5 days of symptom onset in critically ill patients with H1N1 influenza 6
Formulation and Administration
- Oseltamivir is available as capsules (30 mg, 45 mg, 75 mg) and as a powder for oral suspension (6 mg/mL when reconstituted) 4, 3
- For the oral suspension, dosing volumes are 4, 3:
- 30 mg dose = 5 mL
- 45 mg dose = 7.5 mL
- 60 mg dose = 10 mL
- 75 mg dose = 12.5 mL
Clinical Efficacy
- Oseltamivir is effective against both influenza A and B viruses 1, 2, 7, 8
- Treatment reduces the duration of illness by up to 1.5 days and severity by up to 38% when initiated promptly 7
- It also reduces the incidence of secondary complications such as otitis media, bronchitis, pneumonia, and sinusitis 7, 5
Common Side Effects and Management
- Gastrointestinal effects (nausea, vomiting, diarrhea) are the most common adverse events 4, 7, 5
- These side effects are typically mild and transient, resolving within 1-2 days 5
- Taking oseltamivir with food can significantly reduce gastrointestinal side effects 4, 7, 5
Important Considerations
- Higher doses (150 mg twice daily) have not shown additional benefit for influenza A but may improve virologic response in influenza B 9
- Standard 5-day treatment duration is appropriate for most patients; extended treatment has limited evidence except in critically ill patients 6
- Resistance to oseltamivir is rare and generally of limited clinical relevance 5