What is the recommended treatment for influenza A?

Treatment for Influenza A

Oseltamivir 75 mg orally twice daily for 5 days is the first-line treatment for influenza A in adults and adolescents ≥13 years, and should be initiated as soon as possible, ideally within 48 hours of symptom onset. 1, 2

Primary Treatment Recommendation

• Oseltamivir (Tamiflu) is the antiviral drug of choice for influenza A treatment across all age groups, with demonstrated efficacy in reducing illness duration by approximately 24 hours and potentially decreasing hospitalization rates and need for subsequent antibiotics. 3, 1

• The standard adult dose is 75 mg orally twice daily for 5 days, which is FDA-approved for patients ≥2 weeks of age who have been symptomatic for no more than 48 hours. 2, 1

• Treatment provides greatest benefit when initiated within 12-36 hours of symptom onset, with earlier initiation associated with faster symptom resolution—treatment within 12 hours reduces illness duration by an additional 74.6 hours compared to treatment at 48 hours. 1, 4

Pediatric Dosing (Weight-Based)

For children ≥12 months, oseltamivir dosing is weight-based for 5 days: 3, 1

• ≤15 kg (≤33 lb): 30 mg twice daily
• 15-23 kg (33-51 lb): 45 mg twice daily
• 23-40 kg (51-88 lb): 60 mg twice daily
• >40 kg (>88 lb): 75 mg twice daily

For infants <12 months: 3, 1

• 9-11 months: 3.5 mg/kg per dose twice daily
• Term infants 0-8 months: 3 mg/kg per dose twice daily
• Preterm infants: Dosing varies by postmenstrual age (1.0-3.0 mg/kg twice daily depending on gestational age)

High-Priority Groups Requiring Immediate Treatment

Treatment should be initiated empirically without waiting for laboratory confirmation in the following high-risk populations, even if presenting beyond 48 hours: 1, 5

• Children <2 years of age
• Adults ≥65 years
• Pregnant and postpartum women (up to 2 weeks postpartum)
• Immunocompromised patients
• Patients with chronic medical conditions (pulmonary, cardiovascular, renal, metabolic, diabetes, hemoglobinopathies)
• Hospitalized patients with confirmed or suspected influenza
• Patients with severe, progressive, or complicated illness (pneumonia, respiratory failure)

Alternative Antiviral Agents

• Zanamivir (inhaled) is an acceptable alternative at 10 mg (two 5-mg inhalations) twice daily for 5 days, approved for ages ≥7 years for treatment and ≥5 years for prophylaxis. 3, 6

• Zanamivir should NOT be used in patients with underlying airways disease (asthma, COPD) due to risk of serious bronchospasm. 6

• Peramivir (IV) may be considered for severely ill patients with concerns about oral absorption or gastrointestinal intolerance. 1

• Amantadine and rimantadine are NOT recommended due to high resistance rates (>99%) among current influenza A strains and should not be used unless resistance patterns change significantly. 3, 1, 7

Renal Dose Adjustment

• For patients with creatinine clearance <30 mL/min, reduce oseltamivir dose by 50% to 75 mg once daily for treatment. 1, 5

• Oseltamivir is not recommended for patients with end-stage renal disease not undergoing dialysis. 2

Extended Treatment Duration

• Standard treatment duration is 5 days for uncomplicated influenza. 3, 1, 2

• Longer duration may be considered for immunocompromised patients, critically ill patients, or those with persistent fever after 6 days of treatment, though data supporting extended therapy are limited. 1, 8

Managing Adverse Effects

• Nausea and vomiting occur in approximately 10-15% of patients taking oseltamivir and are the most common adverse effects. 1, 9

• Taking oseltamivir with food significantly reduces gastrointestinal side effects—this is a critical counseling point that can improve adherence. 1, 4

• Gastrointestinal symptoms are typically mild, transient, and resolve within 1-2 days. 9, 4

• Diarrhea may occur more frequently in infants <1 year of age. 1

Critical Pitfalls to Avoid

• Do not delay treatment while awaiting laboratory confirmation in patients with clinical influenza during community outbreaks, especially in high-risk populations—empiric treatment should be started immediately. 1, 5

• Do not withhold treatment beyond 48 hours in hospitalized or severely ill patients—these patients may still derive mortality benefit from antiviral therapy even when started later in the disease course. 1, 5

• Do not use amantadine or rimantadine for influenza A treatment due to widespread resistance. 3, 1

• Immunocompromised or very elderly patients may benefit from treatment despite lack of documented fever. 5

Managing Secondary Bacterial Complications

• Previously healthy adults with acute bronchitis complicating influenza do not routinely require antibiotics, but antibiotics should be considered if worsening symptoms develop. 1, 5

• High-risk patients with lower respiratory features should receive antibiotics such as co-amoxiclav or tetracycline. 1, 5

• For non-severe influenza-related pneumonia, oral co-amoxiclav or tetracycline is preferred and should be administered within 4 hours of admission. 1

• For severe influenza-related pneumonia, IV combination therapy with a broad-spectrum β-lactamase stable antibiotic plus a macrolide is recommended. 1

Prophylaxis Considerations

• Post-exposure prophylaxis with oseltamivir 75 mg once daily for 7-10 days after last known exposure should be initiated within 48 hours of exposure. 3, 1

• Seasonal prophylaxis with oseltamivir 75 mg once daily for up to 6 weeks during community outbreaks is effective, with >70% protective efficacy demonstrated in clinical trials. 1, 9

• Oseltamivir is not a substitute for annual influenza vaccination, which remains the primary prevention strategy. 2, 6