Management of Influenza
For uncomplicated influenza in otherwise healthy adults, initiate oseltamivir 75 mg twice daily for 5 days only if the patient presents within 48 hours of symptom onset with fever >38°C and acute influenza-like illness; antibiotics are not routinely indicated unless bacterial complications develop. 1
Antiviral Treatment Criteria
All three criteria must be met for standard antiviral therapy: 2
- Acute influenza-like illness (fever, cough, myalgias, malaise)
- Documented fever >38°C
- Symptom duration ≤48 hours
Dosing regimen: 2
- Oseltamivir 75 mg orally every 12 hours for 5 days
- Reduce dose by 50% (75 mg once daily) if creatinine clearance <30 mL/min
Important Exceptions to Standard Criteria
Immunocompromised or very elderly patients may receive antivirals despite lack of documented fever, as they often cannot mount adequate febrile responses. 2, 1
Severely ill hospitalized patients, particularly if immunocompromised, may benefit from oseltamivir even when started >48 hours after symptom onset, though evidence for benefit in this scenario is limited. 2, 1 This recommendation prioritizes potential mortality reduction in high-risk patients despite lack of robust supporting data.
Alternative Antiviral Options
Baloxavir marboxil is available as a single-dose oral treatment for patients ≥5 years old who present within 48 hours of symptom onset. 3 Take with or without food, but avoid concurrent administration with dairy products, calcium-fortified beverages, or supplements containing calcium, iron, magnesium, selenium, or zinc, as these significantly reduce absorption. 3
Zanamivir (inhaled) is an alternative neuraminidase inhibitor but is NOT recommended for patients with underlying airways disease (asthma, COPD) due to risk of fatal bronchospasm. 4 If zanamivir is considered despite airways disease, it requires careful respiratory monitoring, close observation, and availability of fast-acting bronchodilators. 4
Antibiotic Management
Uncomplicated Influenza Without Pneumonia
Previously healthy adults with acute bronchitis complicating influenza do NOT routinely require antibiotics in the absence of pneumonia. 2, 1 This is a critical pitfall—bacterial co-infection typically develops 4-5 days after initial symptoms, not at presentation. 1
Consider antibiotics only if worsening symptoms develop: 2, 1
- Recrudescent fever (fever returns after initial improvement)
- Increasing dyspnea
High-risk patients should receive antibiotics if lower respiratory tract features are present, even without confirmed pneumonia. 2 High-risk groups include elderly patients, those with chronic cardiac/pulmonary disease, immunocompromised individuals, and those with diabetes or renal disease.
Preferred oral antibiotic regimens: 2
- Co-amoxiclav (first-line)
- Tetracycline (alternative first-line)
- Macrolide (clarithromycin or erythromycin) for penicillin-allergic patients
- Fluoroquinolone with pneumococcal and staphylococcal coverage (levofloxacin or moxifloxacin)
Non-Severe Influenza-Related Pneumonia
Most patients can be treated with oral antibiotics. 2
Preferred oral regimens: 2
- Co-amoxiclav
- Tetracycline
When oral therapy is contraindicated, use parenteral antibiotics: 2
- IV co-amoxiclav
- Second-generation cephalosporin (cefuroxime)
- Third-generation cephalosporin (cefotaxime)
Antibiotics must be administered within 4 hours of hospital admission. 2
Duration: 7 days for uncomplicated pneumonia. 2
Severe Influenza-Related Pneumonia
Treat immediately with parenteral combination therapy: 2
Preferred regimen: 2
- IV broad-spectrum beta-lactamase stable antibiotic (co-amoxiclav, cefuroxime, or cefotaxime)
- PLUS IV macrolide (clarithromycin or erythromycin)
Alternative regimen: 2
- IV fluoroquinolone with enhanced pneumococcal activity (levofloxacin)
- PLUS broad-spectrum beta-lactamase stable antibiotic or macrolide
Be vigilant for Staphylococcus aureus pneumonia, which is more common during influenza outbreaks than in typical community-acquired pneumonia. 1
Duration: 2
- 10 days for severe, microbiologically undefined pneumonia
- 14-21 days if S. aureus or Gram-negative enteric bacilli confirmed or suspected
Switch from IV to oral antibiotics as soon as clinical improvement occurs and temperature has been normal for 24 hours, provided no contraindication to oral route exists. 2
Hospitalization and Discharge Criteria
Patients should remain hospitalized if they have ≥2 of the following unstable clinical factors: 2, 1
- Temperature >37.8°C
- Heart rate >100/min
- Respiratory rate >24/min
- Systolic blood pressure <90 mmHg
- Oxygen saturation <90%
- Inability to maintain oral intake
- Abnormal mental status
Review patients within 24 hours before discharge. 2
Follow-Up and Re-Consultation Triggers
Patients should re-consult immediately if: 2
- Shortness of breath at rest or with minimal activity
- Painful or difficult breathing
- Coughing up bloody sputum
- Drowsiness, disorientation, or confusion
- Fever persists 4-5 days without improvement or worsens
- Initial improvement followed by recurrent high fever
- No improvement within 2 days of starting antivirals
Arrange follow-up for all patients with significant complications or worsening of underlying disease with their general practitioner or hospital clinic. 2, 1
Key Clinical Pitfalls
Avoid unnecessary antibiotics in uncomplicated influenza—bacterial co-infection typically develops days after initial presentation, not at onset. 1
Do not delay antiviral treatment for laboratory confirmation during confirmed community outbreaks; clinical diagnosis is sufficient when influenza is circulating locally. 5, 6
Greatest benefit from antivirals occurs when started within 24 hours of symptom onset, though treatment within 48 hours still provides benefit. 7, 6
Neuraminidase inhibitors reduce illness duration by approximately 24 hours, decrease complications, reduce antibiotic use, and may decrease hospitalizations and mortality. 7, 8, 6
Influenza vaccination remains the primary preventive measure; antivirals are adjunctive, not alternatives to vaccination. 7, 9