What are the treatment options for influenza (flu)?

Treatment of Influenza

Start oseltamivir 75 mg twice daily for 5 days immediately in all hospitalized patients, severely ill patients, or high-risk individuals with suspected influenza, ideally within 48 hours of symptom onset—but do not withhold treatment in severely ill patients even beyond 48 hours. 1, 2

Who Should Receive Antiviral Treatment

Immediate Treatment Indicated (Do Not Wait for Testing)

• All hospitalized patients with suspected or confirmed influenza, regardless of symptom duration 1, 2
• Severely ill or progressive illness at any age, regardless of timing 2
• High-risk patients including:
  • Children under 2 years and adults ≥65 years 3, 2
  • Pregnant and postpartum women (up to 2 weeks postpartum) 2
  • Immunocompromised patients 2
  • Chronic medical conditions (pulmonary, cardiac, renal, metabolic disorders) 2

Outpatient Treatment (Within 48 Hours of Symptom Onset)

• Previously healthy outpatients may benefit from antivirals if started within 48 hours, though benefit is modest (reduces illness duration by approximately 24 hours) 1, 4
• The American Thoracic Society requires all three criteria for outpatient treatment: acute influenza-like illness, fever >38°C, and symptomatic for ≤48 hours 1

Do NOT Treat with Antivirals

• Healthy patients presenting >48 hours after symptom onset in outpatient settings—the treatment window has closed 1, 5
• Exception: Hospitalized/severely ill patients benefit even beyond 48 hours, particularly if immunocompromised 1, 2

Antiviral Drug Options

First-Line: Oseltamivir (Tamiflu)

• Standard dosing: 75 mg orally twice daily for 5 days 3, 2, 6
• Pediatric dosing (weight-based, see detailed table): 3
  • Infants 0-8 months (term): 3 mg/kg/dose twice daily
  • Infants 9-11 months: 3.5 mg/kg/dose twice daily
  • Children ≥12 months: weight-tiered dosing (30-75 mg twice daily)
• Renal adjustment: 75 mg once daily if creatinine clearance 10-30 mL/min 3, 2
• Pregnancy: Safe to use; high-risk pregnant women should be treated 2
• May be given with meals to improve GI tolerability 3

Alternative: Baloxavir (Xofluza)

• Single-dose oral therapy for patients ≥5 years (previously ≥12 years) 3, 7
• Dosing: 40 mg (40-80 kg) or 80 mg (≥80 kg) as single dose 3, 7
• WHO conditionally recommends baloxavir for non-severe influenza in high-risk patients 8
• Must be given within 48 hours of symptom onset 7

Alternative: Zanamivir (Relenza)

• Inhaled therapy: 10 mg (two 5-mg inhalations) twice daily for 5 days 3, 9
• Approved for treatment in patients ≥7 years 3, 9
• Contraindicated in asthma/COPD due to risk of severe, life-threatening bronchospasm 2, 9
• Use only if oseltamivir cannot be taken 1

Alternative: Peramivir

• Single IV infusion: 600 mg over 15-30 minutes (adults); 12 mg/kg up to 600 mg (children 2-12 years) 3
• Useful when oral/inhaled routes not feasible 3
• Not recommended for prophylaxis 3

Avoid: Amantadine/Rimantadine

• Not mentioned in current guidelines due to widespread resistance 10

When to Add Antibiotics

Do NOT Routinely Add Antibiotics

• Previously healthy adults with uncomplicated influenza or acute bronchitis do not need antibiotics 1, 2
• Antibiotics should not be used systematically without evidence of bacterial infection 2

Add Antibiotics Immediately If:

• Worsening symptoms after initial improvement (suggests bacterial superinfection) 1, 2, 5
• High-risk patients with lower respiratory tract features 1
• Confirmed or suspected bacterial pneumonia on imaging or clinical grounds 1
• Signs of bacterial superinfection (typically 4-5 days after initial symptoms): 5
  • New or recrudescent fever after improvement
  • Increasing dyspnea or respiratory distress
  • Purulent sputum production
  • Pneumonia on examination

Antibiotic Selection for Influenza-Related Pneumonia

Non-severe pneumonia (oral therapy):

• First-line: Co-amoxiclav (amoxicillin-clavulanate) or tetracycline 1, 2
• Duration: 7 days for uncomplicated cases 1

Severe pneumonia (parenteral therapy):

• Immediate combination therapy (must be given within 4 hours of admission): 1
  • IV co-amoxiclav OR 2nd/3rd generation cephalosporin (cefuroxime, cefotaxime)
  • PLUS macrolide (clarithromycin or erythromycin)
• Duration: 10 days for severe, microbiologically undefined pneumonia; 14-21 days for confirmed/suspected S. aureus or Gram-negative pneumonia 1
• Switch to oral when clinically improved, afebrile for 24 hours, and oral route feasible 1, 2

Supportive Care

• Antipyretics: Paracetamol (acetaminophen) or ibuprofen for fever, myalgias, headache 3, 1
• Never aspirin in children <16 years due to Reye's syndrome risk 3, 1
• Adequate hydration 3, 1
• Rest 3
• Consider short-course topical decongestants, throat lozenges, saline nose drops 3

Prophylaxis (Post-Exposure)

• Oseltamivir: 75 mg once daily for 10 days after exposure 3
• Baloxavir: Single dose (40 or 80 mg based on weight) 3
• Zanamivir: 10 mg once daily for 10 days 3
• Indicated for high-risk individuals exposed to confirmed influenza who would be at very high risk of hospitalization 8
• Not a substitute for vaccination 6, 7, 9

Critical Pitfalls to Avoid

• Do not delay antiviral treatment while awaiting virological confirmation in hospitalized or high-risk patients 2
• Do not withhold oseltamivir in severely ill hospitalized patients beyond 48 hours—they still benefit 1, 2
• Do not use zanamivir in patients with asthma or COPD 2, 9
• Do not use antibiotics routinely in uncomplicated influenza without bacterial infection evidence 1, 2
• Remember Staphylococcus aureus is more common in influenza-related secondary pneumonia than typical community-acquired pneumonia 2
• Immunocompromised patients may require prolonged antiviral treatment beyond 5 days 2

When Patients Should Re-Consult

• Failure to improve within 48 hours of starting antiviral treatment 3
• Development of worsening symptoms after initial improvement 5
• New or increasing dyspnea 5
• Persistent high fever or recrudescent fever 5
• Signs of dehydration or inability to maintain oral intake 3