What is the recommended treatment for influenza A?

Treatment for Influenza A

Oseltamivir (Tamiflu) 75 mg twice daily for 5 days is the first-line treatment for influenza A in adults and adolescents, and should be initiated as soon as possible, ideally within 48 hours of symptom onset. 1, 2

Recommended Dosing by Age Group

Adults and Adolescents (≥13 years)

• Standard dose: 75 mg orally twice daily for 5 days 3, 1, 2
• Treatment reduces illness duration by approximately 24 hours and may decrease hospitalization rates and need for subsequent antibiotics 1, 4

Pediatric Patients (Weight-Based Dosing)

For children ≥12 months: 3, 5, 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

For infants <12 months: 3, 5

• 9-11 months: 3.5 mg/kg per dose twice daily
• 0-8 months: 3 mg/kg per dose twice daily
• Term infants ≥2 weeks: FDA-approved for treatment 2

For preterm infants (consult pediatric infectious disease for <28 weeks): 3

• <38 weeks postmenstrual age: 1.0 mg/kg twice daily
• 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily

• 40 weeks postmenstrual age: 3.0 mg/kg twice daily

Renal Impairment

• Creatinine clearance <30 mL/min: Reduce to 75 mg once daily 1, 6
• Not recommended for end-stage renal disease patients not on dialysis 2

Timing of Treatment Initiation

Treatment is most effective when started within 48 hours of symptom onset, with greatest benefit occurring within the first 24 hours. 1, 7, 4 However, important exceptions exist:

• Hospitalized patients with severe illness should receive treatment even if >48 hours from symptom onset, particularly if immunocompromised 1, 6
• Treatment initiated within 12 hours reduces illness duration by an additional 74.6 hours compared to treatment at 48 hours 7
• Treatment within 24 hours provides an additional 53.9 hours of benefit compared to 48-hour initiation 7

Who Should Receive Treatment

Offer treatment immediately to: 3, 1, 5

• All hospitalized patients with presumed influenza
• Patients with severe, complicated, or progressive illness
• Children <2 years (high-risk for complications)
• Patients at high risk of complications (immunocompromised, chronic respiratory/cardiac disease, elderly)

Consider treatment for: 3, 1

• Any otherwise healthy patient with influenza, especially if within 48 hours of onset
• Healthy children living with siblings <6 months or household contacts with high-risk conditions

Alternative Antiviral Agents

While oseltamivir is preferred, alternatives include:

• Zanamivir (inhaled): 10 mg (two 5-mg inhalations) twice daily for 5 days, approved for ages ≥7 years 3

  • Contraindicated in patients with chronic respiratory disease (asthma, COPD) due to bronchospasm risk 3

• Peramivir (IV): For severely ill patients with concerns about oral absorption 6

Amantadine and rimantadine are NOT recommended due to high resistance rates among current influenza A strains 3, 5

Duration and Extended Treatment

• Standard treatment duration: 5 days 3, 2
• Consider longer duration for: 6
  • Persistent fever after 6 days with evidence of ongoing viral replication
  • Immunocompromised patients with prolonged viral shedding
  • Critically ill patients, though evidence for benefit is limited 8

Double-dose oseltamivir (150 mg twice daily) has NOT been shown to improve outcomes and is not recommended 3, 8

Common Pitfalls and Important Considerations

Do Not Delay Treatment

• Do not wait for laboratory confirmation before initiating treatment 5, 4
• Negative rapid antigen tests should not rule out influenza due to low sensitivity 5

Adverse Effects

• Nausea and vomiting occur in ~10-15% of patients 3, 9
• Taking oseltamivir with food reduces gastrointestinal side effects 2, 9, 7
• Diarrhea may occur in infants <1 year 5
• Despite reports from Japan, neuropsychiatric events have not been definitively linked to oseltamivir 3, 5

Managing Persistent Fever

If fever persists beyond 3-5 days, strongly suspect bacterial coinfection: 6

• Investigate with respiratory cultures, blood cultures, and chest imaging
• Empirically treat bacterial coinfection in patients with extensive pneumonia, respiratory failure, or hypotension
• Consider antiviral resistance testing if persistent viral replication after 7-10 days of treatment 6

Resistance Monitoring

• Current influenza A strains remain largely susceptible to oseltamivir 3, 5
• Resistance is rare and mutants show reduced transmissibility and pathogenicity 7
• Continuous CDC monitoring guides treatment recommendations 5

Prophylaxis Considerations

While treatment is the focus, oseltamivir is also approved for prophylaxis:

• Post-exposure prophylaxis: 75 mg once daily for 10 days (initiate within 48 hours of exposure) 3
• Seasonal prophylaxis: 75 mg once daily for up to 6 weeks during community outbreaks 9
• Prophylaxis is NOT a substitute for annual vaccination 2