What is the recommended treatment for influenza?

Treatment of Influenza

Start oseltamivir 75 mg orally twice daily for 5 days as soon as influenza is suspected, ideally within 48 hours of symptom onset, without waiting for laboratory confirmation. 1, 2, 3

Who Should Receive Antiviral Treatment

Immediate treatment is indicated for:

• Any hospitalized patient with suspected or confirmed influenza, regardless of symptom duration 1, 2
• Patients with severe, complicated, or progressive illness including pneumonia or respiratory failure 1, 2
• High-risk patients including:
  • Children under 2 years of age 2, 4
  • Adults 65 years and older 2, 4
  • Pregnant and postpartum women (within 2 weeks of delivery) 2, 4
  • Immunocompromised patients 1, 2
  • Patients with chronic medical conditions (cardiac, pulmonary, renal, hepatic, neurologic, hematologic, or metabolic disorders including diabetes) 2, 4

Treatment should be considered for:

• Otherwise healthy outpatients who present within 48 hours of symptom onset, as early treatment shortens illness duration by approximately 1 day and reduces severity by up to 38% 1, 5
• Patients with siblings under 6 months or with high-risk conditions 1

First-Line Antiviral Medications

Oseltamivir (oral) is the preferred first-line agent for both influenza A and B 1, 2, 3:

• Adults and adolescents ≥13 years: 75 mg orally twice daily for 5 days 1, 2, 3
• Pediatric dosing (weight-based): 1, 2, 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

• Infants <12 months: 3 mg/kg per dose twice daily 4, 3

Alternative agents include:

• Zanamivir (inhaled): 10 mg (two 5-mg inhalations) twice daily for 5 days, approved for ages ≥7 years for treatment 1, 6
  • Not recommended for patients with underlying airway disease (asthma, COPD) due to risk of severe bronchospasm 6
• Peramivir (IV): For severely ill patients with concerns about oral absorption 1, 4
• Baloxavir (oral): Conditionally recommended for non-severe influenza in high-risk patients 7

Timing and Duration Considerations

Treatment is most effective when started within 48 hours of symptom onset, with greatest benefit occurring within 12-36 hours 1, 2, 8. However, treatment should still be initiated beyond 48 hours in hospitalized patients, severely ill patients, or high-risk groups, as it may still provide mortality benefit 1, 2, 4.

Standard treatment duration is 5 days 1, 2, 3. Longer duration may be considered for patients with persistent fever after 6 days, immunocompromised patients, or critically ill patients 4.

Renal Dose Adjustment

For patients with creatinine clearance <30 mL/min, reduce oseltamivir dose by 50% to 75 mg once daily 2, 4, 3. Oseltamivir is not recommended for end-stage renal disease patients not undergoing dialysis 3.

Managing Adverse Effects

Common side effects of oseltamivir include nausea (12-15%) and vomiting (2.5-14%) 1, 2, 5. Taking oseltamivir with food significantly reduces gastrointestinal side effects 2, 5. Diarrhea may occur in infants <1 year 4. Neuropsychiatric events have not been definitively linked to oseltamivir 1, 4.

Antibiotic Use for Complications

Do not routinely prescribe antibiotics for uncomplicated influenza 1, 2. Antibiotics are indicated only when bacterial co-infection is suspected or confirmed 1.

For influenza-related bacterial pneumonia:

• Non-severe pneumonia: Oral co-amoxiclav or tetracycline, administered within 4 hours of admission 1, 2
• Severe pneumonia: IV combination therapy with broad-spectrum β-lactamase stable antibiotic (co-amoxiclav or cefuroxime/cefotaxime) plus a macrolide (clarithromycin or erythromycin) 1, 2
• Target likely bacterial pathogens: S. pneumoniae, S. pyogenes, and S. aureus including MRSA 1

Antibiotics should be considered for:

• Previously healthy adults with worsening symptoms (recrudescent fever or increasing dyspnea) 1, 2
• High-risk patients with lower respiratory tract features 1, 2

Prophylaxis Recommendations

Post-exposure prophylaxis: Oseltamivir 75 mg once daily for 10 days, initiated within 48 hours of exposure 2, 4, 3

Seasonal prophylaxis: Oseltamivir 75 mg once daily for up to 6 weeks during community outbreaks 2, 4, 3. In immunocompromised patients, may continue for up to 12 weeks 3.

Antiviral prophylaxis is not a substitute for annual influenza vaccination, which remains the primary prevention strategy 1, 3, 6.

Diagnostic Testing Considerations

Do not delay treatment while awaiting laboratory confirmation in high-risk patients or during known influenza activity 1, 2. Rapid molecular assays (RT-PCR) are preferred when testing is performed, as they are highly sensitive and specific with results available in <20 minutes 1. Positive rapid tests are helpful for reducing unnecessary testing and promoting antimicrobial stewardship, but negative results should not exclude influenza due to suboptimal sensitivity 1.

Antiviral Resistance Monitoring

During the 2018-2019 season, >99% of influenza A(H1N1)pdm09 and all influenza A(H3N2) viruses tested were susceptible to oseltamivir, zanamivir, and peramivir 1. Amantadine and rimantadine are not recommended due to high resistance rates among current influenza A strains 4, 9. Clinicians should monitor CDC guidance for updates on circulating virus resistance patterns 1.