Management of Influenza A
Start oseltamivir 75 mg orally twice daily for 5 days immediately for any patient with suspected or confirmed influenza A, ideally within 48 hours of symptom onset, but do not withhold treatment in high-risk or severely ill patients presenting beyond 48 hours. 1, 2
Immediate Treatment Initiation
Oseltamivir is the antiviral treatment of choice for influenza A. 3, 1 The standard adult dosage is 75 mg orally twice daily for 5 days. 3, 1 Treatment should be initiated as early as possible, ideally within 48 hours of symptom onset when maximum benefit occurs. 1, 2
Criteria for Standard Treatment
All three criteria should ideally be present for routine treatment: 2
- Acute influenza-like illness (abrupt onset with respiratory symptoms)
- Fever >38°C in adults
- Symptom duration ≤48 hours
Critical Exceptions: Treat Beyond 48 Hours
Do not withhold oseltamivir in the following populations, even if presenting >48 hours after symptom onset: 1, 4
- All hospitalized patients with suspected influenza 1, 4
- Severely ill or progressively worsening patients 1, 4
- Immunocompromised patients (including those on long-term corticosteroids, chemotherapy, HIV, transplant recipients) 3, 4
- Children <2 years of age, particularly infants <6 months 3, 1
- Adults ≥65 years 1, 4
- Pregnant or postpartum women 1, 4
- Patients with chronic medical conditions: 1, 4
- Chronic respiratory disease (asthma, COPD, cystic fibrosis, bronchiectasis)
- Chronic cardiac disease (congenital heart disease, heart failure, ischemic heart disease)
- Chronic renal disease (nephrotic syndrome, chronic renal failure, transplant)
- Chronic liver disease (cirrhosis)
- Diabetes mellitus requiring medication
- Neurological diseases with muscle weakness or cerebral palsy
- Residents of long-term care facilities
Evidence supporting late treatment: Multiple studies demonstrate significant mortality benefit when oseltamivir is initiated up to 96 hours after symptom onset in hospitalized and high-risk patients (OR for death = 0.21). 1, 4
Renal Dose Adjustment
Reduce dose by 50% (75 mg once daily for 5 days) if creatinine clearance is <30 mL/min. 3, 1 Oseltamivir is not recommended for patients with end-stage renal disease not undergoing dialysis. 5
Pediatric Dosing (Weight-Based)
For children, administer twice daily for 5 days: 3, 1
- ≤15 kg: 30 mg twice daily
- >15-23 kg: 45 mg twice daily
- >23-40 kg: 60 mg twice daily
- >40 kg: 75 mg twice daily
- Infants 9-11 months: 3.5 mg/kg per dose twice daily
- Term infants 0-8 months: 3 mg/kg per dose twice daily
Expected Clinical Benefits
When initiated within 48 hours: 1, 6, 7
- Reduces illness duration by 1-1.5 days (approximately 24-36 hours)
- Reduces risk of pneumonia by 50%
- Reduces otitis media in children by 34%
- Decreases antibiotic use by 35%
- Significant mortality benefit in hospitalized/high-risk patients (OR = 0.21)
- Faster return to normal activities and work
Antibiotic Management
Do not routinely prescribe antibiotics for uncomplicated influenza or acute bronchitis in previously healthy adults without pneumonia. 3, 2
When to Add Antibiotics
Consider antibiotics in the following situations: 3, 2
- Worsening symptoms after initial improvement (recrudescent fever or increasing dyspnea)
- High-risk patients with lower respiratory tract features (productive cough, focal chest findings)
- Confirmed pneumonia on chest X-ray
- Clinical deterioration despite oseltamivir treatment
Preferred Antibiotic Choices
For non-severe pneumonia (oral therapy): 3, 2
- Co-amoxiclav (first choice)
- Tetracycline (e.g., doxycycline)
- Macrolide (clarithromycin or erythromycin) if intolerant to above
For severe pneumonia (parenteral therapy): 3, 2
- IV co-amoxiclav OR cefuroxime/cefotaxime PLUS a macrolide
Common Adverse Effects
Nausea and vomiting are the most common side effects, occurring in approximately 10-15% of patients. 3, 1, 6 These are typically mild, transient, and rarely lead to discontinuation. 1, 6 Taking oseltamivir with food reduces gastrointestinal symptoms. 6, 7
Critical Pitfalls to Avoid
- Do not wait for laboratory confirmation before starting treatment in high-risk patients during influenza season. Rapid antigen tests have poor sensitivity, and negative results should not exclude treatment. 1, 4
- Do not withhold oseltamivir based solely on time since symptom onset in high-risk or hospitalized patients. Mortality benefit persists even when treatment starts up to 96 hours after onset. 1, 4
- Do not reflexively add antibiotics for viral influenza symptoms alone. Bacterial superinfection typically develops 4-5 days after initial symptoms, not at presentation. 2
- Immunocompromised or very elderly patients may not mount adequate febrile responses. Treat based on clinical suspicion even without documented fever. 3, 1, 2
Monitoring and Follow-Up
For hospitalized patients, monitor twice daily (more frequently if severe): 3
- Temperature, respiratory rate, pulse, blood pressure
- Mental status
- Oxygen saturation and inspired oxygen concentration
Discharge criteria: Patients should have <2 of the following unstable factors before discharge: 3, 2
- Temperature >37.8°C
- Heart rate >100/min
- Respiratory rate >24/min
- Systolic blood pressure <90 mmHg
- Oxygen saturation <90%
Post-Exposure Prophylaxis
Consider oseltamivir 75 mg once daily for 10 days for: 1, 4
- Household contacts of influenza-infected persons, especially high-risk individuals
- Unvaccinated healthcare workers during institutional outbreaks
- Residents of long-term care facilities during outbreaks (continue ≥2 weeks or until 1 week after outbreak ends)
Prophylaxis should be initiated within 48 hours of exposure for maximum effectiveness. 4