What is the treatment for influenza (flu)?

Treatment of Influenza

Oral oseltamivir (Tamiflu) 75 mg twice daily for 5 days is the antiviral drug of choice for treating influenza in adults and adolescents, ideally initiated within 48 hours of symptom onset. 1, 2

Antiviral Treatment Indications

Start antiviral therapy immediately for:

• Any hospitalized patient with suspected or confirmed influenza, regardless of timing or vaccination status 3
• Patients with severe, complicated, or progressive illness 3
• High-risk patients (elderly, immunocompromised, chronic cardiac/respiratory disease, pregnant women) 4, 3
• Outpatients presenting within 48 hours of symptom onset who have acute influenza-like illness with fever >38°C 1, 4

Critical point: Do not delay treatment while awaiting laboratory confirmation—clinical diagnosis is sufficient, and treatment within 24 hours provides maximum benefit. 3

Dosing Regimens by Age and Weight

Adults

• Standard dose: 75 mg orally twice daily for 5 days 1, 2
• Renal impairment (CrCl <30 mL/min): 75 mg once daily for 5 days 1, 4

Children ≥12 months (weight-based)

• ≤15 kg: 30 mg twice daily for 5 days 1

• 15-23 kg: 45 mg twice daily for 5 days 1

• 23-40 kg: 60 mg twice daily for 5 days 1

• 40 kg: 75 mg twice daily for 5 days 1

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
• Preterm infants: Dosing varies by postmenstrual age (1.0-3.0 mg/kg per dose twice daily) 1

Alternative Antiviral Options

Zanamivir (Relenza)

• Adults and children ≥7 years: 10 mg (two 5-mg inhalations) twice daily for 5 days 1, 5
• Equally acceptable alternative for patients without chronic respiratory disease 1
• Contraindicated in asthma or COPD due to risk of serious bronchospasm 5, 6

Peramivir (Rapivab)

• Adults: 600 mg IV infusion over 15-30 minutes, single dose 1
• Children 2-12 years: 12 mg/kg (max 600 mg) IV over 15-30 minutes, single dose 1
• Limited to outpatients with uncomplicated influenza; efficacy not established for hospitalized patients 1

Baloxavir

• Patients ≥12 years, 40-80 kg: 40 mg orally, single dose 1
• Patients ≥12 years, ≥80 kg: 80 mg orally, single dose 1

Extended Treatment Window Considerations

Severely ill hospitalized patients, particularly if immunocompromised, may benefit from oseltamivir even when started >48 hours after symptom onset, though evidence is limited. 1, 4, 3 Oseltamivir may reduce mortality when initiated up to 5 days after symptom onset in critically ill patients, particularly with H1N1. 4

Elderly and immunocompromised patients may not mount adequate febrile responses and should still receive treatment even without documented fever. 1, 4

Expected Treatment Benefits

Antiviral therapy provides:

• Reduction in illness duration by approximately 24 hours (up to 1.5 days in controlled trials) 1, 3, 7, 8
• Greater benefit (2.5 days reduction) in high-risk patients with fever at enrollment 6, 9
• Possible reduction in hospitalization rates 3, 7
• Decreased subsequent antibiotic use 1, 3
• Faster return to normal activities 3, 9

Note: No antiviral drug has been proven to reduce overall mortality or prevent serious influenza-related complications in outpatient trials, though this has not been ruled out. 1

Antibiotic Management

Influenza WITHOUT Pneumonia

• Previously healthy adults with acute bronchitis complicating influenza do NOT routinely require antibiotics 1, 3
• Consider antibiotics only if worsening symptoms develop (recrudescent fever, increasing dyspnea) 1, 3
• Strongly consider antibiotics for high-risk patients (COPD, chronic cardiac disease, immunocompromised) when lower respiratory tract features are present 1, 3

Influenza-Related Pneumonia

All patients with influenza-related pneumonia require antibiotics, initiated within 4 hours of hospital admission. 1, 3

Preferred oral regimens:

• Co-amoxiclav or tetracycline as first-line 1, 3
• Macrolides (clarithromycin, erythromycin) or respiratory fluoroquinolones (levofloxacin, moxifloxacin) as alternatives 1

Severe pneumonia requiring parenteral therapy:

• IV co-amoxiclav or 2nd/3rd generation cephalosporin (cefuroxime, cefotaxime) PLUS macrolide 1, 3
• Alternative: Respiratory fluoroquinolone plus broad-spectrum β-lactamase stable antibiotic 1
• Must cover Staphylococcus aureus in addition to typical community-acquired pneumonia pathogens 3

Duration: 7 days for uncomplicated pneumonia; 10 days for severe, microbiologically undefined pneumonia 1

Common Pitfalls to Avoid

• Never use aspirin in children with influenza due to risk of Reye syndrome 3
• Do not withhold oseltamivir from high-risk patients presenting slightly beyond 48 hours—they may still benefit 4, 3
• Zanamivir is contraindicated in patients with underlying airways disease (asthma, COPD) due to risk of life-threatening bronchospasm 5, 8
• Monitor vigilantly for secondary bacterial pneumonia, particularly Staphylococcus aureus, especially during influenza outbreaks 4, 3
• Oseltamivir's most common adverse effect is nausea (~10%); administer with food to reduce gastrointestinal symptoms 2, 8

Important Limitations

• Antivirals are not a substitute for annual influenza vaccination 2, 5
• Emergence of resistance mutations could decrease drug effectiveness; prescribers should consider available CDC information on influenza drug susceptibility patterns 2, 5
• Oseltamivir is not recommended for end-stage renal disease patients not undergoing dialysis 2
• Treatment does not reduce transmission of influenza to others 5