What is the recommended treatment for influenza (flu)?

Influenza Treatment

For influenza, start oseltamivir 75 mg twice daily for 5 days immediately in all high-risk patients and those with severe illness, ideally within 48 hours of symptom onset but even beyond 48 hours if illness is progressive or complicated. 1, 2

Immediate Treatment Indications

Never delay antiviral treatment while awaiting laboratory confirmation—clinical diagnosis alone is sufficient to initiate therapy. 2 Treatment should begin empirically based on clinical presentation during influenza season. 3

High-Risk Patients Requiring Treatment

Antiviral therapy with neuraminidase inhibitors is mandatory for the following groups with suspected or confirmed influenza: 3, 1

• Children under 2 years (highest risk in infants under 6 months) 3
• Adults 65 years or older 3, 1
• Pregnant women and postpartum women (within 2 weeks of delivery) 3, 1
• Chronic medical conditions: pulmonary disease including asthma, cardiovascular disease (except hypertension alone), renal disease, hepatic disease, diabetes, neurologic disorders, immunosuppression 3, 1
• Morbidly obese patients (BMI ≥40) 3
• Nursing home residents 3
• Any hospitalized patient with suspected influenza, regardless of timing 3, 2

Previously Healthy Patients

For otherwise healthy outpatients without high-risk conditions, antiviral treatment can be considered if initiated within 48 hours of symptom onset, based on clinical judgment to reduce symptom duration by approximately 1 day. 3, 1

First-Line Antiviral Medications

Oseltamivir (Preferred)

Oseltamivir is the first-line treatment for influenza across all age groups. 1, 2

Adult dosing: 75 mg orally twice daily for 5 days 1, 2, 4

Pediatric dosing (2 weeks and older): 4

• Weight-based for children under 1 year: 3 mg/kg twice daily
• 15 kg or less: 30 mg twice daily
• 15.1-23 kg: 45 mg twice daily
• 23.1-40 kg: 60 mg twice daily
• Over 40 kg: 75 mg twice daily

Renal impairment: Reduce dose to 75 mg once daily if creatinine clearance <30 mL/min 1, 4

Administration: Take with food to reduce nausea and vomiting, the most common adverse effects (occurring in 12-15% and 2.5-14% respectively) 1

Alternative Agents

Zanamivir: 10 mg (two inhalations) twice daily for 5 days, approved for patients 7 years and older 3, 5

• Critical contraindication: Do not use in patients with asthma or chronic obstructive pulmonary disease due to risk of severe, potentially fatal bronchospasm 1, 5
• Patients must use bronchodilators before zanamivir if prescribed both 5

Baloxavir: Single-dose option for patients 12 years and older, useful when compliance is a concern 3

Timing of Treatment

Maximum benefit occurs when treatment starts within 24-48 hours of symptom onset, reducing illness duration by 1.5-2.5 days. 1, 6, 7 However, critical exceptions exist:

• Treat beyond 48 hours in patients with severe, complicated, or progressive illness 3, 1
• Treat beyond 48 hours in all hospitalized patients 3, 2
• Treat beyond 48 hours in high-risk patients with worsening symptoms 3, 1

Antibiotic Considerations

Do not routinely prescribe antibiotics for uncomplicated influenza. 2 Antibiotics are indicated only when:

• Confirmed or suspected bacterial pneumonia develops as a complication 2
• Severe influenza-related pneumonia requires immediate broad-spectrum coverage including anti-staphylococcal therapy (for S. aureus), initiated within 4 hours of hospital admission 2
• High-risk patients develop lower respiratory tract features suggesting secondary bacterial infection 2

Critical Pitfalls to Avoid

• Never use aspirin in children with influenza due to Reye syndrome risk 2
• Do not withhold treatment while awaiting test results—empiric therapy based on clinical suspicion is appropriate 3, 2
• Do not assume vaccination eliminates need for treatment—vaccinated high-risk patients still require antivirals if they develop influenza 3
• Remember resistance patterns: Amantadine and rimantadine are no longer recommended due to widespread resistance 3, 8

Prophylaxis

Antiviral prophylaxis is not a substitute for vaccination but can be used in specific situations: 1, 9

Post-exposure prophylaxis: Oseltamivir 75 mg once daily for 10 days, initiated within 48 hours of exposure to an infected individual 1, 4

Seasonal prophylaxis: Oseltamivir 75 mg once daily for up to 6 weeks during community outbreaks, or up to 12 weeks in immunocompromised patients 1, 4