Treatment for Influenza A
Primary Treatment Recommendation
Oseltamivir 75 mg orally twice daily for 5 days is the first-line treatment for influenza A in adults and adolescents ≥13 years, and should be initiated as soon as possible, ideally within 48 hours of symptom onset. 1, 2
When to Initiate Treatment Immediately (Do Not Wait for Testing)
Treatment should be started empirically without waiting for laboratory confirmation in the following high-risk groups 3, 1:
- All hospitalized patients with suspected influenza, regardless of symptom duration 1
- Patients with severe, progressive, or complicated illness (pneumonia, respiratory failure) 1
- Children <2 years (highest risk in infants <6 months) 3, 1
- Adults ≥65 years 1
- Pregnant and postpartum women (within 2 weeks after delivery) 3, 1
- Immunocompromised patients (HIV, medications, cancer) 3, 1
- Patients with chronic conditions (asthma, COPD, heart disease, diabetes, obesity, neuromuscular disorders) 3, 1
Dosing by Age and Weight
Adults and Adolescents ≥13 years
Pediatric Patients ≥12 months (weight-based) 1, 2:
- ≤15 kg: 30 mg twice daily
15-23 kg: 45 mg twice daily
23-40 kg: 60 mg twice daily
40 kg: 75 mg twice daily
Infants <12 months 1, 2:
- 9-11 months: 3.5 mg/kg per dose twice daily
- 0-8 months: 3 mg/kg per dose twice daily
Preterm Infants (by postmenstrual age) 1:
- <38 weeks: 1.0 mg/kg twice daily
- 38-40 weeks: 1.5 mg/kg twice daily
40 weeks: 3.0 mg/kg twice daily
Timing Considerations
The greatest benefit occurs when treatment is initiated within 48 hours of symptom onset, reducing illness duration by approximately 24 hours (1-1.5 days) and severity by up to 38%. 3, 1, 4 However, earlier initiation within 12-36 hours provides progressively greater benefit, reducing illness duration by up to 3.1 days compared to treatment at 48 hours. 1, 5
Critical exception: For hospitalized patients, severely ill patients, or high-risk groups, treatment should be initiated even beyond 48 hours as it may still provide mortality benefit. 3, 1
Duration of Treatment
- Standard duration: 5 days for uncomplicated influenza 1, 2
- Consider longer duration (10 days) in immunocompromised patients or those with persistent fever after 6 days, though this remains controversial 1
Renal Dose Adjustment
For creatinine clearance <30 mL/min: reduce dose to 75 mg once daily (50% dose reduction) 1, 6
Oseltamivir is not recommended for end-stage renal disease patients not undergoing dialysis 2
Alternative Antiviral Agents
Zanamivir (inhaled)
- 10 mg (two 5-mg inhalations) twice daily for 5 days 1, 7
- Approved for ages ≥7 years 1, 7
- Contraindicated in patients with underlying airways disease (asthma, COPD) due to risk of serious bronchospasm 7
Peramivir (IV)
- Recommended for severely ill patients with concerns about oral absorption 1
Amantadine and Rimantadine
- NOT recommended due to high resistance rates among current influenza A strains 1
Clinical Benefits
Oseltamivir treatment provides 1, 4:
- Reduces illness duration by 1-1.5 days (24 hours)
- Reduces illness severity by up to 38%
- Reduces pneumonia risk by approximately 50%
- Reduces otitis media in children by 34%
- May decrease hospitalization rates and need for subsequent antibiotics
Adverse Effects and Management
- Nausea and vomiting occur in 10-15% of patients 1, 4
- Taking oseltamivir with food significantly reduces gastrointestinal side effects 1, 4, 5
- Diarrhea may occur in infants <1 year 1
- Neuropsychiatric events have not been definitively linked to oseltamivir 1
- Overall discontinuation rate is low (1.8%) 5
Critical Pitfalls to Avoid
- Do not delay treatment while awaiting laboratory confirmation in high-risk patients or during community outbreaks 3, 1
- Do not withhold treatment beyond 48 hours in hospitalized or severely ill patients, as mortality benefit may still occur 3, 1
- Do not use amantadine or rimantadine for influenza A treatment due to widespread resistance 1
Post-Exposure Prophylaxis
- 75 mg once daily for 10 days, initiated within 48 hours of exposure 1
- Efficacy: 68-89% in household contacts 6