Influenza Treatment
Immediate Treatment Recommendation
All patients with confirmed or suspected influenza who are hospitalized, have severe/progressive illness, or belong to high-risk groups should receive antiviral treatment with oseltamivir as soon as possible, without waiting for diagnostic confirmation, regardless of time since symptom onset. 1, 2, 3
High-Risk Populations Requiring Immediate Treatment
The following groups require immediate antiviral therapy regardless of illness severity or duration:
- Children <2 years of age (especially <6 months who cannot be vaccinated) 1, 3
- Adults ≥65 years 2, 4
- Pregnant women and up to 2 weeks postpartum 2, 4
- Immunocompromised patients 2, 4
- Patients with chronic medical conditions including heart disease, diabetes, chronic lung disease, chronic kidney disease, neurologic disorders 1, 2, 4
First-Line Antiviral: Oseltamivir
Adults and Adolescents (≥13 years)
- Dosage: 75 mg orally twice daily for 5 days 2, 5
- May be taken with or without food, though tolerability improves with food 5
Pediatric Dosing (Weight-Based)
| Weight | Treatment Dose | Volume (6 mg/mL suspension) |
|---|---|---|
| ≤15 kg | 30 mg twice daily | 5 mL |
| 15.1-23 kg | 45 mg twice daily | 7.5 mL |
| 23.1-40 kg | 60 mg twice daily | 10 mL |
| >40 kg | 75 mg twice daily | 12.5 mL |
- 0-8 months: 3 mg/kg per dose twice daily (0.5 mL/kg of 6 mg/mL suspension)
- 9-11 months: 3.5 mg/kg per dose twice daily
Treatment duration: 5 days for all ages 5
Critical Timing Considerations
Treatment should be initiated within 48 hours of symptom onset for maximum benefit, reducing illness duration by approximately 36 hours (26% reduction) and decreasing complications including otitis media by 34% in children. 1, 3, 6
However, treatment should NOT be withheld in high-risk or hospitalized patients even if >48 hours have passed, as observational data demonstrate mortality reduction when started within 5 days in hospitalized adults (adjusted OR 0.50). 1, 2, 7
Do not delay treatment while awaiting diagnostic test results—initiate empirically based on clinical suspicion during influenza season. 1, 3
Alternative Antiviral Options
Zanamivir (Inhaled)
- Dosage: 10 mg (two 5-mg inhalations) twice daily for 5 days 8
- Approved for: Treatment in patients ≥7 years; prophylaxis in patients ≥5 years 8
- Critical contraindication: NOT recommended for patients with underlying airways disease (asthma, COPD) due to risk of fatal bronchospasm 8
- Patients using bronchodilators should use them BEFORE zanamivir 8
Peramivir (Intravenous)
- Alternative for patients unable to take oral/inhaled medications 1, 3
- Approved for: Children ≥6 months for treatment 3
Baloxavir
- Single-dose oral option approved for prophylaxis (≥12 years) 1
- Reduced household transmission by 92% (1% vs 13% with placebo) when given within 48 hours of exposure 1
Treatment Considerations for Otherwise Healthy Outpatients
Antiviral treatment may be considered for previously healthy symptomatic outpatients with confirmed/suspected influenza if: 1, 4
- Treatment can be initiated within 48 hours of illness onset
- Patient has siblings/household contacts who are <6 months old or have high-risk conditions
- Clinical judgment suggests benefit based on illness severity
Managing Bacterial Coinfection
Add empiric antibiotics to antiviral therapy if: 2, 4
- Initial presentation with severe disease
- Clinical deterioration after initial improvement
- Failure to improve after 3-5 days of antiviral treatment
First-line antibiotic for children <12 years: Co-amoxiclav 125/31 mg, 5 mL three times daily 3
Penicillin-allergic children (1-2 years): Clarithromycin 62.5 mg twice daily 3
Diagnostic Testing Approach
Preferred tests: RT-PCR or molecular assays (sensitivity 86-100%) 1, 4
Rapid antigen tests: Positive results are helpful for treatment decisions, but negative results should NOT rule out influenza due to low sensitivity (10-80%) and should not delay treatment in high-risk patients. 1, 3
For hospitalized patients: PCR confirmation should be considered, but presumptive treatment should start before results. 1
Common Pitfalls and Important Caveats
Side Effects
- Vomiting occurs in 5-15% of children taking oseltamivir but is generally mild and transient 1, 3
- Taking oseltamivir with food reduces gastrointestinal side effects 5, 6
- Despite historical concerns from Japan, controlled trials have failed to establish a link between oseltamivir and neuropsychiatric events 1, 3
Antiviral Resistance
- Do NOT use amantadine or rimantadine—high resistance rates (>99%) persist among circulating influenza A viruses 1, 2, 3
- During 2019-2020 season, >99% of influenza A(H1N1)pdm09 and B viruses remained susceptible to oseltamivir, zanamivir, and peramivir 1
- Monitor local resistance patterns as they can change 1
What NOT to Do
- Do NOT use corticosteroids as adjunctive therapy for seasonal influenza—associated with increased mortality and bacterial superinfection 2, 7
- Do NOT use double-dose oseltamivir—no benefit demonstrated over standard dosing in randomized trials 1
- Do NOT withhold treatment in high-risk patients presenting >48 hours after symptom onset 1, 2, 7
Special Populations
- Renal impairment: Adjust oseltamivir dose in moderate/severe renal dysfunction 5
- Immunocompromised patients: May require extended prophylaxis up to 12 weeks 5
- Preterm infants: Use adjusted dosing based on postmenstrual age 3
Chemoprophylaxis Indications
Post-exposure prophylaxis (initiate within 48 hours of exposure): 1, 5
- Adults/adolescents ≥13 years: 75 mg once daily for 10 days
- Children 1-12 years: Weight-based dosing (same mg amounts as treatment, but once daily) for 10 days
- High-risk household contacts of infected persons
- During community outbreaks: Up to 6 weeks duration
Chemoprophylaxis is NOT a substitute for annual influenza vaccination, which remains the primary prevention strategy. 1, 5