What is the recommended treatment for Influenza A (Flu A)?

Treatment for Influenza A

For patients with confirmed or suspected Influenza A, initiate oseltamivir 75 mg orally twice daily for 5 days as soon as possible, ideally within 48 hours of symptom onset, though treatment should not be withheld in severely ill or hospitalized patients even beyond this window. 1, 2, 3

Who Requires Immediate Antiviral Treatment

Mandatory treatment groups where oseltamivir should be started immediately regardless of symptom duration include: 4, 2

• Hospitalized patients with confirmed or suspected influenza 4, 2
• Patients with severe, progressive, or complicated illness (e.g., pneumonia, respiratory failure) 4, 2
• High-risk patients including: 4, 2
  • Children <2 years (especially infants <6 months who have highest mortality) 4
  • Adults ≥65 years 4
  • Pregnant and postpartum women (within 2 weeks of delivery) 4
  • Immunocompromised patients 4
  • Patients with chronic conditions (pulmonary including asthma, cardiovascular except hypertension alone, renal, hepatic, hematological, metabolic including diabetes, or neurologic disorders) 4

Standard Dosing Regimens

Adults and Adolescents ≥13 Years

• Oseltamivir 75 mg orally twice daily for 5 days 1, 3
• Take with food to reduce gastrointestinal side effects 1, 5

Pediatric Patients (Weight-Based Dosing)

For children 1-12 years: 1, 3

• ≤15 kg: 30 mg twice daily
• 15.1-23 kg: 45 mg twice daily
• 23.1-40 kg: 60 mg twice daily

• 40 kg: 75 mg twice daily

For infants <12 months: 1

• 9-11 months: 3.5 mg/kg twice daily
• 0-8 months: 3 mg/kg twice daily
• Preterm infants: dose adjusted by postmenstrual age (1.0-3.0 mg/kg twice daily) 1

Renal Dose Adjustment

• Creatinine clearance <30 mL/min: reduce dose by 50% (75 mg once daily for adults) 4

Critical Timing Considerations

The 48-hour window is a guideline, not an absolute cutoff: 4, 2

• Greatest benefit occurs when treatment starts within 24 hours of symptom onset (reduces illness duration by additional 53.9 hours compared to starting at 48 hours) 5
• Treatment within 12 hours provides even greater benefit (additional 74.6 hours reduction) 5
• For severely ill, hospitalized, or high-risk patients, initiate treatment even if >48 hours from symptom onset, as observational studies show benefit up to 4-5 days after onset in reducing mortality and morbidity 4, 2

Alternative Antiviral Agents

When oseltamivir is not suitable: 1, 2

• Zanamivir (inhaled): 10 mg (two 5-mg inhalations) twice daily for 5 days, approved for ages ≥7 years 1
• Peramivir (IV): recommended for severely ill patients with concerns about oral absorption 1
• Amantadine and rimantadine are NOT recommended due to high resistance rates among current influenza A strains 1, 2

Extended Treatment Duration

Standard duration is 5 days, but longer treatment may be considered for: 1

• Patients with persistent fever after 6 days 1
• Immunocompromised patients 1
• Critically ill patients 1

Managing Complications

Influenza Without Pneumonia

• Previously healthy adults with acute bronchitis do not routinely require antibiotics 4
• Consider antibiotics if worsening symptoms develop (recrudescent fever or increasing dyspnea) 4
• High-risk patients should receive antibiotics if lower respiratory features present 4
• Preferred oral antibiotics: co-amoxiclav or tetracycline 4

Non-Severe Influenza-Related Pneumonia

• Oral co-amoxiclav or tetracycline preferred 4
• Administer antibiotics within 4 hours of admission 4
• Duration: 7 days for uncomplicated pneumonia 4

Severe Influenza-Related Pneumonia

• IV combination therapy: broad-spectrum β-lactamase stable antibiotic (co-amoxiclav or cefuroxime/cefotaxime) PLUS macrolide (clarithromycin or erythromycin) 4
• Duration: 10 days for severe pneumonia 4
• Empirically treat bacterial coinfection when patients present with initial severe disease, clinical deterioration after initial improvement, or failure to improve after 3-5 days 2

Common Pitfalls and Side Effects

Gastrointestinal effects occur in 10-15% of patients: 1, 5

• Nausea and vomiting are most common 1, 6
• Taking oseltamivir with food significantly reduces GI side effects 1, 6, 5
• Effects are mild, transient, and resolve within 1-2 days 5
• Diarrhea may occur in infants <1 year 1

Important contraindications and warnings: 2

• Do NOT use corticosteroids as adjunctive therapy for seasonal influenza 2
• Neuropsychiatric events have not been definitively linked to oseltamivir 1

Prophylaxis Dosing (When Indicated)

Post-exposure prophylaxis: 1, 3

• 75 mg once daily for 10 days, initiated within 48 hours of exposure 1, 3

Seasonal prophylaxis: 1, 3

• 75 mg once daily for up to 6 weeks during community outbreaks 1, 3
• May extend to 12 weeks in immunocompromised patients 3

Clinical Efficacy

Treatment reduces illness duration by approximately 24 hours in otherwise healthy patients 1, 6, 7

Additional benefits include: 6, 8

• Faster return to normal activities and sleep patterns 8
• Reduced severity of troublesome symptoms (fatigue reduced by 29%, myalgia by 26%) 8
• Decreased incidence of secondary complications (otitis media, bronchitis, pneumonia, sinusitis) 6, 5
• May decrease hospitalization rates and need for subsequent antibiotics 1