What is the recommended treatment for Influenza A?

Treatment for Influenza A

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

Who Should Receive Immediate Antiviral Treatment

Treatment should be started empirically without waiting for laboratory confirmation in the following groups:

• All hospitalized patients with confirmed or suspected influenza, regardless of symptom duration 1
• Patients with severe, progressive, or complicated illness (pneumonia, respiratory failure) 1
• High-risk patients including:
  • Children <2 years and adults ≥65 years 1
  • Pregnant and postpartum women 1
  • Immunocompromised patients 1
  • Patients with chronic conditions (respiratory disease, cardiac disease, diabetes, etc.) 1

Timing of Treatment Initiation

The greatest clinical benefit occurs when treatment is initiated within 12-36 hours of symptom onset, reducing illness duration by up to 3.1 days (41%) compared to treatment at 48 hours 3. However, treatment should still be initiated even beyond 48 hours in hospitalized, severely ill, or high-risk patients as it may provide mortality benefit 1.

Dosing by Age and Weight

Adults and Adolescents (≥13 years)

• Oseltamivir 75 mg orally twice daily for 5 days 1, 2

Pediatric Patients (≥12 months)

Weight-based dosing twice daily for 5 days 1, 2:

• ≤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 (0-11 months)

• 9-11 months: 3.5 mg/kg per dose twice daily 1, 2
• 0-8 months: 3 mg/kg per dose twice daily 1, 2

Preterm Infants

• <38 weeks postmenstrual age: 1.0 mg/kg twice daily 1
• 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily 1

• 40 weeks postmenstrual age: 3.0 mg/kg twice daily 1

Renal Dose Adjustment

For patients with creatinine clearance <30 mL/min, reduce oseltamivir dose by 50% to 75 mg once daily 1. Oseltamivir is not recommended for end-stage renal disease patients not undergoing dialysis 2.

Alternative Antiviral Agents

When oseltamivir is not suitable:

• Zanamivir (inhaled): 10 mg (two 5-mg inhalations) twice daily for 5 days, approved for ages ≥7 years 1, 4
  • Critical caveat: Not recommended for patients with underlying airways disease (asthma, COPD) due to risk of serious bronchospasm 4
• Peramivir (IV): Recommended for severely ill patients with concerns about oral absorption 1
• Amantadine and rimantadine: NOT recommended due to high resistance rates among current influenza A strains 1

Extended Treatment Duration

While standard treatment is 5 days 1, 2, longer duration may be considered for:

• Patients with persistent fever after 6 days 1
• Immunocompromised patients 1
• Critically ill patients 1
• Some evidence suggests doubling the dose to 150 mg twice daily in critically ill adults, though benefit is not definitively established 5

Clinical Benefits of Treatment

Oseltamivir treatment provides:

• Reduction in illness duration by 1-1.5 days (24-36 hours) 1, 6, 7
• Reduction in illness severity by up to 38% 1, 6
• Decreased hospitalization rates 1, 6
• Reduced need for subsequent antibiotics 1, 6
• Lower incidence of complications (11% vs 45% in high-risk patients) 7

Managing Complications and Secondary Bacterial Infections

• Previously healthy adults with acute bronchitis: Do not require routine antibiotics, but consider if worsening symptoms develop 1
• High-risk patients with lower respiratory features: Should receive antibiotics such as co-amoxiclav or tetracycline 1
• Non-severe influenza-related pneumonia: Oral co-amoxiclav or tetracycline, administered within 4 hours of admission 1
• Severe influenza-related pneumonia: IV combination therapy with broad-spectrum β-lactamase stable antibiotic plus macrolide 1

Common Side Effects and How to Minimize Them

• Nausea and vomiting occur in 10-15% of patients 1, 6
• Taking oseltamivir with food significantly reduces gastrointestinal side effects 1, 6, 3
• Diarrhea may occur in infants <1 year 1
• Neuropsychiatric events have not been definitively linked to oseltamivir 1
• Overall discontinuation rate is low (1.8%) 3

Post-Exposure Prophylaxis

For asymptomatic individuals at very high risk (severely immunocompromised, unvaccinated household contacts of high-risk individuals):

• Oseltamivir 75 mg once daily for 7-10 days after last exposure 1, 8
• Must be initiated within 48 hours of exposure 8
• If >48 hours have elapsed, do not give prophylaxis; instead, educate patient to initiate full-dose treatment immediately if symptoms develop 8

Critical Pitfalls to Avoid

• Do not delay treatment while waiting for laboratory confirmation in high-risk or hospitalized patients 1
• Do not withhold treatment beyond 48 hours in severely ill, hospitalized, or high-risk patients 1
• Do not use amantadine or rimantadine due to widespread resistance 1
• Do not use zanamivir in patients with underlying airways disease due to bronchospasm risk 4
• Oseltamivir is not a substitute for annual influenza vaccination 2, 4