What is the recommended treatment for influenza A?

Treatment of Influenza A

The recommended treatment for influenza A is a single neuraminidase inhibitor (NAI), with oral oseltamivir being the preferred agent, initiated as soon as possible within 48 hours of symptom onset for a standard 5-day course. 1

Patient Selection for Antiviral Treatment

Antiviral treatment should be started for:

1. High-priority patients:

   • Hospitalized patients with influenza, regardless of illness duration 1
   • Outpatients with severe or progressive illness 1
   • High-risk patients including those with chronic medical conditions and immunocompromised patients 1
   • Children younger than 2 years and adults ≥65 years 1
   • Pregnant women and those within 2 weeks postpartum 1

2. Other patients:

   • Treatment can be considered for otherwise healthy individuals if started within 48 hours of symptom onset 1

Recommended Antiviral Medications

First-line therapy:

• Oseltamivir (oral) - preferred agent for both influenza A and B 1
  • Adults and adolescents ≥13 years: 75 mg twice daily for 5 days 2
  • Children (dosing by weight) 1:
    • ≤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 9-11 months: 3.5 mg/kg twice daily 1
  • Term infants 0-8 months: 3 mg/kg twice daily 1
  • Preterm infants (by postmenstrual age) 1:
    • <38 weeks: 1 mg/kg twice daily
    • 38-40 weeks: 1.5 mg/kg twice daily

    • 40 weeks: 3 mg/kg twice daily

Alternative options:

• Zanamivir (inhaled): 10 mg (two 5-mg inhalations) twice daily for 5 days for patients ≥7 years 1
• Peramivir (IV): Single dose for adults 1

Timing of Treatment

The timing of antiviral treatment is critical for maximizing efficacy:

• Start treatment as soon as possible after symptom onset 1
• Greatest benefit occurs when started within 24 hours of symptom onset 3
• Treatment within 12 hours can reduce illness duration by an additional 74.6 hours compared to starting at 48 hours 3
• While treatment is most effective within 48 hours, it may still provide benefit in hospitalized patients or those with severe illness even when started later 1

Special Considerations

High-Risk Patients

For patients with chronic respiratory or cardiac diseases, oseltamivir has been shown to:

• Reduce symptom duration by 36.8%
• Reduce complication rates (11% vs. 45% with supportive care only)
• Reduce antibiotic use (37% vs. 69%) 4

Duration of Treatment

• Standard duration: 5 days for uncomplicated influenza 1
• Consider longer duration for:
  • Immunocompromised patients
  • Patients requiring hospitalization for severe lower respiratory tract disease 1

Bacterial Co-infection

• Investigate and empirically treat bacterial co-infection in:
  • Patients with severe initial presentation (extensive pneumonia, respiratory failure, hypotension, fever) 1
  • Patients who deteriorate after initial improvement 1
  • Patients who fail to improve after 3-5 days of antiviral treatment 1

Monitoring for Treatment Failure

Consider antiviral resistance testing in:

• Patients who develop influenza while on or immediately after NAI prophylaxis 1
• Immunocompromised patients with persistent viral replication after 7-10 days of treatment 1
• Patients who received subtherapeutic NAI dosing 1
• Patients with severe influenza who don't improve with treatment 1

Common Pitfalls to Avoid

1. Delaying treatment - Efficacy decreases significantly with each hour of delay; don't wait for test results before initiating treatment in high-risk patients 1, 3

2. Using higher than approved doses - Double-dose oseltamivir has not shown additional benefit and is not recommended 1, 5

3. Inadequate treatment duration - Stopping treatment too early can lead to viral rebound, especially in immunocompromised patients 1

4. Neglecting bacterial co-infections - Secondary bacterial infections are common and may require antibiotics in addition to antiviral therapy 1

5. Relying on serologic testing - Serologic testing is not recommended for diagnosis as it requires paired sera 2-3 weeks apart 1

Remember that antiviral medications are an adjunct to, not a substitute for, annual influenza vaccination 2. Treatment should be initiated based on clinical judgment during influenza season, even before laboratory confirmation in high-risk patients.