What is the recommended treatment for Influenza A?

Treatment for Influenza A

Oseltamivir 75 mg orally twice daily for 5 days is the recommended first-line treatment for adults and adolescents ≥13 years with Influenza A, initiated as soon as possible and ideally within 48 hours of symptom onset. 1, 2

Who Should Receive Immediate Antiviral Treatment

Treatment should be started immediately without waiting for laboratory confirmation in the following groups 1:

• All hospitalized patients with confirmed or suspected influenza, regardless of symptom duration 1
• Patients with severe, progressive, or complicated illness (pneumonia, respiratory failure) 1
• High-risk patients including:
  • Children <2 years of age 1, 3
  • Adults ≥65 years 1
  • Pregnant and postpartum women 1
  • Immunocompromised patients 1
  • Patients with chronic conditions (cardiac, respiratory, renal disease) 1, 4

For these high-risk groups, treatment provides mortality benefit even when initiated beyond 48 hours of symptom onset 1.

Dosing Recommendations by Age Group

Adults and Adolescents (≥13 years)

• Oseltamivir 75 mg orally twice daily for 5 days 1, 2
• Take with food to reduce gastrointestinal side effects 1, 5

Pediatric Patients (≥12 months)

Weight-based dosing 1, 3, 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 (0-11 months)

• 9-11 months: 3.5 mg/kg per dose twice daily 1, 3
• 0-8 months: 3 mg/kg per dose twice daily 1, 3, 2
• Preterm infants: Adjust based on postmenstrual age (1.0-3.0 mg/kg twice daily) 1, 3

Renal Impairment

• Creatinine clearance <30 mL/min: Reduce dose by 50% to 75 mg once daily 1
• Not recommended for end-stage renal disease patients not on dialysis 2

Timing and Clinical Benefits

Greatest benefit occurs when treatment is initiated within 12-36 hours of symptom onset, but treatment should still be given to high-risk patients even if presenting later 1, 6. The evidence shows:

• Reduces illness duration by 1-1.5 days (24-36 hours) 1, 5, 4
• Reduces illness severity by 38-43% 1, 5, 4
• Decreases fever duration by 45% 4
• Reduces hospitalization rates 1, 5
• Decreases secondary complications by 34-76% (including pneumonia and otitis media) 1, 4
• Reduces antibiotic use by 32-46% 1, 4

Earlier initiation provides progressively greater benefit: starting within 12 hours reduces illness duration by 3.1 days (41%) compared to starting at 48 hours 6.

Alternative Antiviral Agents

Zanamivir (Inhaled)

• 10 mg (two 5-mg inhalations) twice daily for 5 days 1, 7
• Approved for ages ≥7 years for treatment, ≥5 years for prophylaxis 1, 7
• Not recommended for patients with underlying airways disease (asthma, COPD) due to risk of serious bronchospasm 1, 7

Peramivir (IV)

• Reserved for severely ill patients with concerns about oral absorption 1
• Approved for children ≥2 years (not ≥6 months as previously stated) 3
• Available via Emergency Use Authorization in certain circumstances 8

Amantadine and Rimantadine

• Not recommended due to high resistance rates among current Influenza A strains 8, 1

Extended Treatment Duration

While standard treatment is 5 days 1, 2, longer duration may be considered for 1:

• Patients with persistent fever after 6 days
• Immunocompromised patients
• Critically ill patients

For critically ill adults, doubling the dose to 150 mg twice daily may be considered, though evidence is mixed 8, 9. One study showed no additional benefit for Influenza A but improved virologic response for Influenza B with higher dosing 9.

Common Side Effects and Management

Nausea and vomiting occur in 10-15% of patients taking oseltamivir 1, 5:

• Taking oseltamivir with food significantly reduces gastrointestinal side effects 1, 5, 6
• Symptoms are typically mild, transient, and occur primarily with first dosing 5, 6
• Diarrhea may occur in infants <1 year 1, 3
• Discontinuation rate is low (1.8%) 6

Neuropsychiatric events have not been definitively linked to oseltamivir in controlled trials and ongoing surveillance 1, 3.

Prophylaxis Considerations

Post-Exposure Prophylaxis

• 75 mg once daily for 7-10 days after last known exposure 8, 1, 10
• Must be initiated within 48 hours of exposure 10
• Reserved for very high-risk individuals (severely immunocompromised, unvaccinated household contacts of high-risk persons) 10

Seasonal Prophylaxis

• 75 mg once daily for up to 6 weeks during community outbreaks 1, 2
• May extend to 12 weeks in immunocompromised patients 2
• Provides >70% protection in unvaccinated adults and 92% in vaccinated high-risk elderly 5

Critical Pitfalls to Avoid

• Do not delay treatment while waiting for laboratory confirmation in high-risk patients—clinical judgment based on symptoms and local influenza activity should guide immediate treatment decisions 1, 3, 11
• Do not withhold treatment beyond 48 hours in high-risk groups—they still benefit from later initiation 1
• Do not use rapid antigen tests alone to rule out influenza due to low sensitivity—negative results should not prevent treatment in high-risk patients 3
• Do not use amantadine or rimantadine due to widespread resistance 8, 1
• Do not use zanamivir in patients with asthma or COPD due to bronchospasm risk 1, 7
• Oseltamivir is not a substitute for annual influenza vaccination, which remains the primary prevention strategy 2, 7, 11

Resistance Monitoring

Current surveillance shows the majority of Influenza A strains remain susceptible to oseltamivir, zanamivir, and peramivir 3. However, continuous monitoring is essential as resistance patterns can change 3, 2. If viral replication persists beyond 7-10 days despite treatment, consider antiviral resistance and consult reference laboratories for resistance testing beyond just H275Y mutation screening 8.