Treatment of Influenza A Positive Patient
Start oseltamivir 75 mg orally twice daily for 5 days immediately for any patient with confirmed influenza A, regardless of timing of presentation, if they are hospitalized, severely ill, or have any high-risk condition including age <2 years or ≥65 years, pregnancy, chronic lung disease (including asthma), diabetes, immunosuppression, or chronic cardiac/neurologic disease. 1, 2
Antiviral Treatment Algorithm
Who Gets Treated?
Immediate treatment is indicated for:
- All hospitalized patients with suspected or confirmed influenza, regardless of illness duration prior to hospitalization 1
- Outpatients with severe or progressive illness, regardless of illness duration 1
- All high-risk patients, including:
For previously healthy outpatients without high-risk features: Treatment can be considered but is not mandatory. The benefit is modest—approximately 24 hours reduction in illness duration when started within 48 hours 1, 3
Timing Considerations
Optimal window: Within 48 hours of symptom onset provides maximum benefit 1, 4
Critical exception: Do not withhold oseltamivir from hospitalized or severely ill patients even if presenting >48 hours after symptom onset, particularly if immunocompromised 1, 2. These patients may still benefit significantly 5, 6
Evidence on late treatment: A study of 1190 patients showed oseltamivir reduced symptom duration even when started ≥48 hours after onset, though the benefit was more modest 5
Dosing Regimen
Standard Adult Dosing
- Oseltamivir 75 mg orally twice daily for 5 days 1, 4
- Take with food to reduce nausea 4, 3
- Renal adjustment: Reduce to 75 mg once daily if creatinine clearance <30 mL/min 1, 4
Pediatric Dosing (from FDA label)
- Age 2 weeks to <1 year: 3 mg/kg twice daily 4
- Weight ≤15 kg: 30 mg twice daily 1, 4
- Weight 15.1-23 kg: 45 mg twice daily 1, 4
- Weight 23.1-40 kg: 60 mg twice daily 4
- Weight >40 kg: 75 mg twice daily 1, 4
Extended Duration Considerations
Consider longer treatment duration (>5 days) for:
- Immunocompromised patients with documented persistent viral replication 1
- Patients requiring hospitalization for severe lower respiratory disease, pneumonia, or ARDS 1
- Critically ill H1N1-infected ICU patients may benefit from extended treatment 6
Do NOT routinely use higher doses than FDA-approved dosing for seasonal influenza—two randomized controlled trials showed no survival benefit from double-dose therapy 6
Antibiotic Management: When to Add Antibacterials
Do NOT Give Antibiotics
Previously healthy adults with uncomplicated influenza or acute bronchitis without pneumonia do NOT require antibiotics 1, 7, 2
Consider Antibiotics
Add antibiotics if any of the following develop:
- Worsening symptoms after initial improvement (particularly recrudescent fever or increasing dyspnea) 1, 7
- Failure to improve after 3-5 days of antiviral treatment 1
- Signs of bacterial pneumonia on examination or imaging 7
Immediate Antibiotic Therapy Required
Start antibiotics immediately for:
- Patients presenting initially with severe disease (extensive pneumonia, respiratory failure, hypotension) 1
- Confirmed or suspected influenza-related pneumonia 1
- Patients with COPD or other severe pre-existing illnesses who develop lower respiratory features 1
Antibiotic Selection
For non-severe influenza-related pneumonia (oral therapy):
- First-line: Co-amoxiclav OR tetracycline (e.g., doxycycline) 1, 7, 2
- Alternative: Macrolide (clarithromycin preferred over azithromycin for better H. influenzae activity) OR fluoroquinolone with pneumococcal and staphylococcal activity 1
For severe influenza-related pneumonia (parenteral therapy):
- Immediate combination therapy: IV co-amoxiclav OR 2nd/3rd generation cephalosporin (cefuroxime or cefotaxime) PLUS macrolide (clarithromycin or erythromycin) 1, 7, 2
- Must cover S. aureus—this is critical as staphylococcal pneumonia is a common and severe complication 2
- Administer within 4 hours of admission 7
Duration of antibiotics:
- 7 days for non-severe, uncomplicated pneumonia 7
- 10 days for severe, microbiologically undefined pneumonia 7
- 14-21 days for confirmed/suspected S. aureus or Gram-negative pneumonia 7
Switch to oral: When clinical improvement occurs, temperature normal for 24 hours, and oral route feasible 7
Common Pitfalls to Avoid
Never delay antiviral treatment while awaiting laboratory confirmation—clinical diagnosis is sufficient 2
Never use aspirin in children <16 years with influenza due to Reye syndrome risk 7, 2
Never prescribe zanamivir to patients with any underlying airways disease (asthma, COPD), regardless of severity—risk of fatal bronchospasm 8
Never withhold oseltamivir from high-risk or hospitalized patients even if presenting beyond 48 hours 1, 2, 8
Never rely on negative rapid antigen tests to rule out influenza—they have low sensitivity 2
Always remember to cover S. aureus when treating influenza-related pneumonia with antibiotics 2
Adverse Effects and Tolerability
Most common side effect: Nausea in approximately 10% of patients 1, 3
- Transient and generally occurs only with first dosing 9
- Managed by taking oseltamivir with food 4, 3, 9
- Can use mild anti-emetic medication if needed 1
Overall discontinuation rate is low (1.8%) 9
Expected Benefits
Anticipated positive effects of oseltamivir:
- Reduction of illness duration by approximately 24 hours (up to 1.5 days when started early) 1, 3, 9
- Possible reduction in hospitalization 1, 2
- Reduction in subsequent antibiotic use 1, 2
- Hastens return to normal activity 2, 3
Earlier initiation provides progressively greater benefit: Starting within 12 hours of fever onset reduced illness duration by 3.1 days (41%) more than starting at 48 hours 9
Mortality benefit: Current evidence does not definitively demonstrate reduction in overall mortality, but does not rule it out 1