Treatment of Influenza A
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, 3
Who Must Receive Immediate Antiviral Treatment
Treatment should be started immediately without waiting for laboratory confirmation in the following groups: 1, 2
- Any hospitalized child or adult with suspected or confirmed influenza 1, 2
- Patients with severe, complicated, or progressive illness including pneumonia or respiratory failure 1, 2
- High-risk patients regardless of illness duration: 1, 2
Pediatric Dosing (Weight-Based)
For children ≥12 months: 1, 2, 3
- ≤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
- 9-11 months: 3.5 mg/kg per dose twice daily
- 0-8 months (term): 3 mg/kg per dose twice daily
For preterm infants (by postmenstrual age): 1, 2
- <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
Treatment Duration and Timing
- Standard duration: 5 days for uncomplicated influenza 1, 2, 3
- Extended duration: Consider 10 days in immunocompromised patients or those with persistent fever after 6 days 1, 4
- Optimal timing: Treatment provides greatest benefit when started within 24-36 hours of symptom onset, but should still be offered to hospitalized or severely ill patients even beyond 48 hours 1, 5
Clinical Benefits of Treatment
When initiated within 48 hours, oseltamivir: 2, 4, 5
- Reduces illness duration by approximately 24 hours 2, 4, 5
- Decreases pneumonia risk by approximately 50% 4
- Reduces hospitalization rates 2
- Provides 82% reduction in in-patient death for hospitalized patients (OR 0.18) 4
- Decreases otitis media incidence by 34% in children 4
Alternative Antiviral Agents
- Dose: 10 mg (two 5-mg inhalations) twice daily for 5 days
- Approved for: Ages ≥7 years for treatment, ≥5 years for prophylaxis 1, 6
- Contraindication: NOT recommended for patients with underlying respiratory disease (asthma, COPD) due to risk of serious bronchospasm 6
- Recommended for severely ill patients with concerns about oral absorption or gastrointestinal dysfunction 1, 2
Baloxavir: 1
- Single-dose oral agent that may be considered as alternative when compliance is a concern 1
- Availability of oral suspension formulation may be limited 1
Agents NOT Recommended
Amantadine and rimantadine should NOT be used due to high resistance rates (>99%) among currently circulating influenza A strains. 1, 2
Renal Dose Adjustment
For patients with creatinine clearance <30 mL/min: 2, 4
- Reduce oseltamivir dose by 50% to 75 mg once daily for treatment
- Oseltamivir is NOT recommended for end-stage renal disease patients not on dialysis 3
Managing Adverse Effects
- Nausea and vomiting occur in 10-15% of patients 1, 2
- Mitigation strategy: Take oseltamivir with food to reduce gastrointestinal symptoms 2, 3
- Diarrhea may occur in infants <1 year (7% incidence) 1
Neuropsychiatric events: 1
- Have been reported but not definitively linked to oseltamivir in controlled trials 1
Prophylaxis Considerations
Post-exposure prophylaxis: 2, 4, 3
- Dose: 75 mg once daily for 7-10 days
- Must be initiated within 48 hours of exposure 2, 4
- Efficacy: 68-89% in household contacts 4
- Dose: 75 mg once daily for up to 6 weeks during community outbreaks
- Protective efficacy >70% in unvaccinated healthy adults 4
Critical Pitfalls to Avoid
- Do not delay treatment while awaiting laboratory confirmation in high-risk patients or during community outbreaks 1, 2
- Do not withhold treatment beyond 48 hours in hospitalized or severely ill patients—late treatment still provides mortality benefit 1, 4
- Do not use amantadine or rimantadine for current influenza A strains 1, 2
- Do not prescribe zanamivir to patients with asthma or COPD due to bronchospasm risk 6
- Remember that antiviral treatment is NOT a substitute for annual influenza vaccination 1, 3