What is the recommended treatment for influenza (flu)?

Treatment of Influenza

Oral oseltamivir 75 mg twice daily for 5 days is the first-line antiviral treatment for influenza in adults and adolescents, and should be initiated as soon as possible, ideally within 48 hours of symptom onset. 1, 2

Antiviral Treatment Recommendations

When to Treat with Antivirals

Treatment should be offered as early as possible for the following patients, regardless of vaccination status or whether symptoms began more than 48 hours prior: 1

• Any hospitalized patient with clinically presumed or confirmed influenza 1
• Patients with severe, complicated, or progressive illness attributable to influenza 1
• High-risk patients including those with chronic pulmonary disease, cardiovascular disease, immunocompromised states, age ≥65 years, or age <2 years 1

For outpatients with uncomplicated influenza, treatment is most beneficial when started within 48 hours of symptom onset, though earlier initiation (within 24 hours) provides the greatest benefit. 1, 3

Oseltamivir Dosing (First-Line Agent)

Adults and adolescents ≥13 years: 75 mg orally twice daily for 5 days 1, 2

Children ≥12 months (weight-based): 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 9-11 months: 3.5 mg/kg per dose twice daily 1

Term infants 0-8 months: 3 mg/kg per dose twice daily 1

Renal dosing adjustment: Reduce dose by 50% (75 mg once daily) if creatinine clearance <30 mL/minute 1, 4

Alternative Antiviral Agents

Zanamivir (inhaled): 10 mg (two 5-mg inhalations) twice daily for 5 days is an equally acceptable alternative for patients ≥7 years old without chronic respiratory disease (asthma, COPD). 1, 5 This agent is more difficult to administer but has comparable efficacy. 1

Peramivir (intravenous): Single 600 mg IV infusion (12 mg/kg in children 2-12 years, maximum 600 mg) is approved for acute uncomplicated influenza in patients ≥2 years who have been symptomatic ≤2 days. 1 However, efficacy in hospitalized patients with serious influenza has not been established. 1

Baloxavir: Single oral dose (40 mg for 40-80 kg; 80 mg for ≥80 kg) for patients ≥12 years. 1

Clinical Benefits of Antiviral Treatment

Timely antiviral treatment provides the following benefits:

• Reduces illness duration by approximately 24 hours in otherwise healthy patients 1, 3
• Reduces symptom severity by up to 38% 4
• Decreases risk of acute otitis media by 34% in children 1-5 years 1
• May reduce hospitalizations and need for subsequent antibiotics 4
• Reduces influenza-associated mortality when started within 48 hours (or even within 5 days) in hospitalized patients 1

In high-risk patients, treatment benefits are even greater, with reductions in illness duration of 2.5 days in high-risk patients with fever and up to 7 days in patients >50 years with severe symptoms. 6

Important Treatment Considerations

Treatment beyond 48 hours: While optimal benefit occurs with early treatment, patients hospitalized with moderate-to-severe or progressive disease should still receive antivirals even if presenting >48 hours after symptom onset, as some benefit has been demonstrated. 1

Immunocompromised or elderly patients: May benefit from treatment despite lack of documented fever, as they may be unable to mount an adequate febrile response. 1, 4

No benefit from double-dose therapy: Standard dosing is recommended; higher doses provide no additional benefit. 1

Antibiotic Use: When NOT to Prescribe

Do not routinely prescribe antibiotics for uncomplicated influenza with cold symptoms or acute bronchitis. 1, 4 Influenza is a viral illness, and antibiotics have no effect on viral infections. 7

Consider antibiotics only if secondary bacterial infection develops: 1, 4

• Recrudescent fever after initial improvement
• Increasing dyspnea or breathlessness
• New focal chest signs suggesting pneumonia
• High-risk patients with lower respiratory tract features

First-line antibiotic choices (if indicated): Co-amoxiclav or tetracycline (e.g., doxycycline); alternatives include macrolides (clarithromycin) or fluoroquinolones with pneumococcal activity. 1, 4

Supportive Care

• Antipyretics for fever control (acetaminophen or ibuprofen) 4
• Adequate hydration and rest 4
• Symptom monitoring for signs of complications 4

Antiviral Resistance

Amantadine and rimantadine should not be used due to high levels of resistance in circulating influenza strains. 1 Current neuraminidase inhibitors (oseltamivir, zanamivir, peramivir) maintain good activity against most circulating strains. 1

Common Pitfalls to Avoid

• Vomiting occurs in approximately 5-15% of oseltamivir-treated patients, particularly children; taking medication with food may improve tolerability. 1, 2
• Zanamivir should be avoided in patients with asthma or COPD due to risk of bronchospasm. 1, 8
• Do not withhold antivirals from hospitalized patients simply because they present >48 hours after symptom onset. 1
• Neuropsychiatric adverse effects have been reported with oseltamivir but causality has not been established. 1