What is the recommended treatment for influenza (flu)?

Treatment of Influenza

Start antiviral treatment immediately with oseltamivir 75 mg orally twice daily for 5 days in all hospitalized patients, high-risk individuals (including children <2 years, adults ≥65 years, pregnant women, immunocompromised patients, and those with chronic medical conditions), and anyone with severe or progressive illness, regardless of symptom duration. 1, 2, 3

Who Should Receive Antiviral Treatment

Immediate Treatment Required (Do Not Wait for Testing)

• All hospitalized patients with suspected or confirmed influenza 1, 2
• High-risk outpatients including:
  • Children younger than 2 years (highest risk in infants <6 months) 4, 2
  • Adults ≥65 years 4, 2
  • Pregnant women and postpartum women within 2 weeks of delivery 2
  • Immunocompromised patients 4, 2
  • Patients with chronic pulmonary, cardiovascular, renal, hepatic, hematologic, metabolic, or neurologic conditions 4, 2
• Patients with severe or progressive illness at any time point 4, 1

Consider Treatment (Clinical Judgment)

• Previously healthy outpatients with confirmed or suspected influenza who present within 48 hours of symptom onset 4, 1
• Immunocompromised or very elderly patients even without documented fever (they may not mount adequate febrile response) 4
• Severely ill hospitalized patients may benefit even if started >48 hours after symptom onset 4, 5

Antiviral Medication Regimens

First-Line Treatment: Oseltamivir

• Adults and adolescents ≥13 years: 75 mg orally twice daily for 5 days 1, 2, 3
• Renal impairment (CrCl <30 mL/min): Reduce dose to 75 mg once daily 4, 2, 3
• Children 2 weeks to 12 years: Weight-based dosing 3:
  • ≤15 kg: 30 mg twice daily
  • 15.1-23 kg: 45 mg twice daily
  • 23.1-40 kg: 60 mg twice daily

  • 40 kg: 75 mg twice daily

• Infants <1 year: 3 mg/kg twice daily 3
• Take with food to reduce nausea 2, 3

Alternative Options

• Zanamivir: 10 mg (two 5-mg inhalations) twice daily for 5 days in patients ≥7 years 1, 6
  • Contraindicated in patients with asthma or COPD due to bronchospasm risk 2, 6
• Peramivir: Intravenous option for patients unable to take oral/inhaled medications 1, 2

Special Considerations for Duration

• Immunocompromised patients or severe lower respiratory disease: Consider longer treatment duration beyond 5 days 1, 2
• Standard 5-day course is adequate for most patients 1, 3

Timing of Treatment Initiation

Treatment is most effective when started within 24 hours of symptom onset but should be initiated as soon as possible within 48 hours for outpatients. 1, 2, 7 However, do not withhold treatment from hospitalized or severely ill patients even if >48 hours have passed since symptom onset. 4, 1, 5

Management of Bacterial Complications

When to Add Antibiotics

Do NOT routinely use antibiotics for uncomplicated influenza. 4, 5 Add antibiotics only when:

• Severe initial presentation suggesting bacterial coinfection 1, 5
• Clinical deterioration after initial improvement 1, 5
• Failure to improve after 3-5 days of antiviral treatment 1
• Worsening symptoms (recrudescent fever or increasing dyspnea) 4, 5
• High-risk patients with lower respiratory features 4

Antibiotic Selection by Severity

Non-severe influenza-related pneumonia (oral therapy):

• First-line: Co-amoxiclav or tetracycline 4, 5
• Alternative (penicillin allergy): Macrolide (clarithromycin/erythromycin) or respiratory fluoroquinolone (levofloxacin/moxifloxacin) 4, 5
• Administer within 4 hours of admission 4
• Duration: 7 days for uncomplicated cases 4

Severe influenza-related pneumonia (parenteral therapy):

• Preferred regimen: IV broad-spectrum β-lactamase stable antibiotic (co-amoxiclav or cefuroxime/cefotaxime) PLUS macrolide (clarithromycin/erythromycin) 4, 1, 5
• Alternative: Respiratory fluoroquinolone with pneumococcal/staphylococcal coverage plus broad-spectrum β-lactam 4
• Duration: 10 days (extend to 14-21 days if S. aureus or Gram-negative bacilli suspected) 4
• Switch to oral when temperature normal for 24 hours and clinical improvement occurs 4

Common Pitfall

Staphylococcus aureus (including MRSA) is more common during influenza outbreaks than in routine community-acquired pneumonia—consider adding MRSA coverage if not responding to initial therapy. 4, 5

What NOT to Do

• Do NOT use corticosteroids for influenza treatment unless clinically indicated for other reasons (e.g., COPD exacerbation, septic shock) 1
• Do NOT routinely administer immunoglobulin preparations 1
• Do NOT use antibiotics for uncomplicated influenza without evidence of bacterial infection 5, 2
• Do NOT delay antiviral treatment while awaiting diagnostic test results 4, 1

Prophylaxis Recommendations

Post-Exposure Prophylaxis (initiate within 48 hours of exposure)

• Oseltamivir: 75 mg once daily for 10 days 2, 3
• Target: High-risk unvaccinated individuals exposed to confirmed influenza 2
• Immunocompromised patients: May continue up to 12 weeks 3

Seasonal Prophylaxis During Community Outbreak

• Oseltamivir: 75 mg once daily for up to 6 weeks 2, 3
• Zanamivir: 10 mg once daily for 28 days 6
• Not a substitute for vaccination—use only as adjunct in high-risk situations 2, 3

Monitoring for Antiviral Resistance

Monitor for resistance particularly in:

• Patients developing influenza while on or immediately after neuraminidase inhibitor prophylaxis 1
• Immunocompromised patients with persistent viral replication despite treatment 1
• Patients with severe influenza not improving with treatment 1