What are the treatment options for influenza (flu)?

Treatment of Influenza

Start antiviral treatment immediately with oseltamivir 75 mg orally twice daily for 5 days in all hospitalized patients, those with severe/progressive illness, and high-risk outpatients with confirmed or suspected influenza, ideally within 48 hours of symptom onset but do not withhold treatment beyond this window in severely ill patients. 1, 2

Immediate Antiviral Therapy Indications

Do not delay treatment while awaiting laboratory confirmation - empiric therapy based on clinical judgment is appropriate when influenza is circulating in the community. 3

Mandatory Treatment Groups

Antiviral treatment is strongly recommended for:

• All hospitalized patients with confirmed or suspected influenza, regardless of symptom duration 3, 1
• Patients with severe, complicated, or progressive illness at any stage 3
• High-risk patients including:
  • Children aged <2 years (highest risk in infants <6 months) 3
  • Adults aged ≥65 years 3
  • Pregnant or postpartum women (within 2 weeks after delivery) 3
  • Persons with chronic pulmonary disease (including asthma), cardiovascular disease (except hypertension alone), renal, hepatic, hematological, metabolic (including diabetes), or neurologic conditions 3
  • Immunocompromised patients (including HIV infection or immunosuppressive medications) 3

Optional Treatment Groups

Consider antiviral treatment for previously healthy, symptomatic outpatients not at high risk if treatment can be initiated within 48 hours of illness onset, based on clinical judgment. 3

Antiviral Medication Selection and Dosing

First-Line: Oseltamivir

• Standard adult dose: 75 mg orally twice daily for 5 days 1, 2
• Renal impairment: 75 mg once daily if creatinine clearance <30 mL/min 4, 2
• Pediatric dosing (≥12 months): Weight-based - 30 mg twice daily (≤15 kg), 45 mg twice daily (>15-23 kg), 60 mg twice daily (>23-40 kg), 75 mg twice daily (>40 kg) 4

Alternative: Zanamivir

• Dose: 10 mg (two inhalations) twice daily for 5 days 5, 6
• Contraindication: Not recommended in patients with underlying airways disease (asthma, COPD) due to risk of serious bronchospasm 5
• Age restriction: Approved for treatment in patients ≥7 years 5

Alternative: Baloxavir

• Conditionally recommended for non-severe influenza in high-risk patients 7
• Also recommended for prophylaxis in exposed asymptomatic persons at very high risk of hospitalization 7

Critical Timing Considerations

Greatest benefit occurs when treatment starts within 24 hours of symptom onset, with diminishing but still meaningful benefit up to 48 hours. 8, 9

However, do not withhold treatment beyond 48 hours in:

• Severely ill or hospitalized patients (may benefit up to 5 days after onset) 3, 1, 4
• Immunocompromised patients 1, 4
• Elderly patients who may not mount adequate febrile responses 4

Observational studies demonstrate that antiviral treatment initiated even 2-5 days after symptom onset reduces mortality in critically ill patients, particularly with H1N1. 3, 4

Antibiotic Management

Do not routinely prescribe antibiotics for uncomplicated influenza in previously healthy adults without evidence of bacterial co-infection. 1, 4

When to Add Antibiotics

Consider antibiotics only when:

• Worsening symptoms develop after initial improvement 1, 4
• High risk for complications or secondary bacterial infection 1, 4
• Confirmed or suspected influenza-related pneumonia 1

Antibiotic Selection When Indicated

First-line oral options:

• Co-amoxiclav (amoxicillin-clavulanate) 1, 4
• Tetracycline 1, 4

Alternative oral options:

• Macrolide 1, 4
• Respiratory fluoroquinolone 1, 4

Severe pneumonia requiring parenteral therapy:

• Intravenous broad-spectrum beta-lactamase stable antibiotic plus macrolide 1

Common Pitfalls and Caveats

Avoid withholding oseltamivir from high-risk patients presenting slightly beyond 48 hours - they may still derive significant benefit, particularly the elderly and immunocompromised. 4

Monitor vigilantly for secondary bacterial pneumonia, which typically develops 4-5 days after initial influenza symptoms. 1 Staphylococcus aureus is more common during influenza outbreaks than in routine community-acquired pneumonia. 1, 4

Immunocompromised and elderly patients may benefit from antiviral treatment even without documented fever, as they may not mount adequate febrile responses. 1, 4

Zanamivir demonstrated comparable efficacy in patients with asthma or chronic pulmonary disease in some studies and reduced pulmonary complications without adversely affecting pulmonary function 6, but FDA labeling contraindicates its use in underlying airways disease due to bronchospasm risk. 5

Oseltamivir may be less effective for influenza B than influenza A, with slower fever resolution and viral shedding in observational studies of Japanese children. 3

Antiviral treatment does not impair normal antibody response to influenza infection and should not replace annual influenza vaccination. 2, 5