What is the recommended treatment for influenza A infection, including antiviral choices and supportive care for adults and children?

Treatment for Influenza A

All children with suspected or confirmed influenza A should receive oseltamivir immediately if they are hospitalized, severely ill, under 2 years of age, or have high-risk conditions—and treatment should begin as soon as possible within 48 hours of symptom onset for maximum benefit, though high-risk and hospitalized patients benefit even when started beyond 48 hours. 1, 2

Who Should Receive Antiviral Treatment

Immediate Treatment Required (Do Not Wait for Testing)

• All hospitalized patients with suspected or confirmed influenza A, regardless of symptom duration or vaccination status 1, 2, 3
• Children under 2 years of age, particularly infants under 6 months who face the highest risk of complications, hospitalization, and death 1, 2
• Severely ill or progressively worsening patients with respiratory distress, pneumonia, or clinical deterioration 1, 2
• High-risk patients including:
  • Adults ≥65 years 1, 2, 4
  • Pregnant and postpartum women 1, 2, 4
  • Immunocompromised patients (HIV, chemotherapy, transplant recipients, long-term corticosteroids) 1, 2, 4
  • Chronic cardiac disease (congenital heart disease, heart failure, coronary artery disease) 1, 2, 4
  • Chronic respiratory disease (asthma, COPD, cystic fibrosis) 1, 2, 4
  • Diabetes mellitus requiring medication 1, 2, 4
  • Chronic renal disease 1, 2, 4
  • Chronic liver disease 1, 2, 4
  • Neurological disorders (cerebral palsy, epilepsy) 1, 2, 4
  • Residents of long-term care facilities 1, 2, 4

Treatment May Be Considered

• Otherwise healthy outpatients presenting within 48 hours of symptom onset who wish to reduce illness duration by approximately 1-1.5 days 1, 2, 3
• Patients with high-risk household contacts (infants <6 months, elderly, immunocompromised) to potentially reduce transmission 1, 2

Recommended Antiviral Medications

First-Line: Oseltamivir (Oral)

Oseltamivir is the preferred first-line antiviral for influenza A treatment in both adults and children. 1, 2, 3

Adult Dosing

• 75 mg orally twice daily for 5 days for adults and adolescents ≥13 years 2, 4, 3
• Reduce to 75 mg once daily if creatinine clearance <30 mL/min 4, 3

Pediatric Dosing (≥12 months)

• ≤15 kg: 30 mg twice daily 2, 3
• >15-23 kg: 45 mg twice daily 2, 3
• >23-40 kg: 60 mg twice daily 2, 3
• >40 kg: 75 mg twice daily 2, 3
• All for 5 days 2, 3

Infant Dosing (<12 months)

• 9-11 months: 3.5 mg/kg per dose twice daily 2, 3
• 0-8 months: 3 mg/kg per dose twice daily 2, 3
• For 5 days 2, 3

Preterm Infants (Postmenstrual Age-Based)

• <38 weeks: 1.0 mg/kg twice daily 2, 3
• 38-40 weeks: 1.5 mg/kg twice daily 2, 3
• >40 weeks: 3.0 mg/kg twice daily 2, 3

Alternative: Zanamivir (Inhaled)

• 10 mg (two 5-mg inhalations) twice daily for 5 days for patients ≥7 years 3, 5
• NOT recommended for patients with underlying airways disease (asthma, COPD) due to risk of life-threatening bronchospasm 5, 6
• Consider when oseltamivir resistance is suspected or confirmed 4, 3

Alternative: Peramivir (IV)

• Reserved for severely ill hospitalized patients with concerns about oral absorption 2, 3
• Approved for children ≥2 years who are not hospitalized and symptomatic ≤2 days 1

NOT Recommended: Amantadine and Rimantadine

• Do not use due to widespread resistance among current influenza A strains 2, 3, 7

Timing of Treatment Initiation

Optimal Window: Within 48 Hours

• Greatest benefit occurs when started within 48 hours of symptom onset, reducing illness duration by 1-1.5 days and severity by up to 38% 1, 2, 4, 3
• Earlier is better—treatment within 12-36 hours provides faster symptom resolution than treatment at 36-48 hours 1, 2

Beyond 48 Hours: Still Treat High-Risk Patients

• Do not withhold treatment in hospitalized, severely ill, or high-risk patients presenting >48 hours after symptom onset 1, 2, 4
• Multiple studies demonstrate significant mortality benefit (OR 0.21 for death within 15 days) when treatment is initiated up to 96 hours after symptom onset in hospitalized patients 4
• Treatment after 48 hours in adults and children with moderate-to-severe or progressive disease has shown benefit and should be strongly considered 1, 4

Do Not Wait for Laboratory Confirmation

• Start treatment empirically based on clinical suspicion during influenza season without waiting for test results 2, 4, 3
• Rapid antigen tests have poor sensitivity (40-60% in adults), and negative results should not exclude treatment in high-risk patients 2
• RT-PCR is the gold standard but takes longer—do not delay treatment while awaiting results 2

Expected Clinical Benefits

Symptom Reduction

• Reduces illness duration by 1-1.5 days (17.6-36 hours) when started within 48 hours 2, 4, 3, 6, 8
• Reduces symptom severity by 30-38% 2, 4, 8
• Faster return to normal activities 4, 8

Complication Prevention

• 50% reduction in pneumonia risk in patients with laboratory-confirmed influenza 2, 4
• 34% reduction in otitis media in children 1, 2, 4
• 35% reduction in secondary complications requiring antibiotics 4
• Decreased hospitalization rates in outpatients 4, 6

Mortality Benefit

• Significant mortality reduction in hospitalized and high-risk patients (OR 0.21 for death within 15 days) 2, 4
• Benefit persists even when treatment is initiated up to 96 hours after symptom onset 4

Viral Shedding

• Reduces quantity and duration of viral shedding, though the clinical significance for transmission prevention is unclear 1, 4, 8

Administration and Tolerability

Oseltamivir Administration

• Can be given with or without food, though taking with food reduces gastrointestinal side effects 2, 8
• Use oral suspension (6 mg/mL concentration) for infants and young children who cannot swallow capsules 2
• If commercial suspension unavailable, pharmacies can compound from capsules 2

Common Adverse Effects

• Vomiting is most common: 15% of treated children vs 9% on placebo, but transient and rarely leads to discontinuation 1, 2, 4
• Nausea occurs in approximately 10-15% of patients 4, 3, 8
• Diarrhea may occur in infants <1 year (7% in clinical trials) 1, 3
• Taking oseltamivir with food significantly reduces nausea and vomiting 2, 8

Important Safety Considerations

• No established link between oseltamivir and neuropsychiatric events—extensive review of controlled trial data and ongoing surveillance has failed to establish causation 1, 2
• Neurologic and neuropsychiatric complications occur in children with influenza in the absence of oseltamivir exposure 1

Treatment Duration and Extended Therapy

Standard Duration

• 5 days is the standard treatment course for both adults and children 2, 4, 3

Consider Extended Duration

• Immunocompromised patients may require treatment beyond 5 days due to prolonged viral shedding 4
• Critically ill patients with persistent fever after 6 days 3
• Clinical judgment should guide extension based on ongoing viral replication and clinical response 4

Post-Exposure Prophylaxis

Indications for Prophylaxis

• High-risk household contacts after exposure to confirmed influenza within 48 hours 2, 4
• Unvaccinated healthcare workers in outbreak settings 4
• Institutional outbreak control in nursing homes—all eligible residents for ≥2 weeks or until 1 week after outbreak ends 4
• Severely immunocompromised patients when vaccination is contraindicated or expected to have low effectiveness 4

Prophylaxis Dosing

• 75 mg once daily for 10 days after household exposure (adults) 4, 3
• Pediatric weight-based dosing once daily for 10 days 4
• Initiate within 48 hours of exposure for maximum benefit 4
• Prophylaxis is not a substitute for vaccination 1, 4

Managing Secondary Bacterial Complications

When to Add Antibiotics

• Do not routinely add antibiotics for viral influenza symptoms alone 4, 3
• Add antibiotics if:
  • New consolidation on chest imaging 4
  • Purulent sputum production 4, 3
  • Clinical deterioration despite oseltamivir 4, 3
  • Elevated inflammatory markers suggesting bacterial infection 4

Antibiotic Choices for Bacterial Superinfection

• Non-severe pneumonia: Oral co-amoxiclav or tetracycline 3
• Severe pneumonia: IV co-amoxiclav or cephalosporin (cefuroxime/cefotaxime) PLUS macrolide (clarithromycin/erythromycin) 3
• Pediatric patients <12 years: Co-amoxiclav 5 mL of suspension 125/31 three times daily 2
• Most common bacterial superinfections are S. pneumoniae, S. aureus, and H. influenzae 4

Critical Pitfalls to Avoid

• Do not delay or withhold treatment while waiting for laboratory confirmation in high-risk patients—this is the most critical error 2, 4
• Do not withhold treatment based on time since symptom onset in hospitalized, severely ill, or high-risk patients 1, 2, 4
• Do not use zanamivir in patients with asthma or COPD due to risk of fatal bronchospasm 5, 6
• Do not use amantadine or rimantadine due to widespread resistance 2, 3
• Do not reflexively add antibiotics for viral symptoms alone—this contributes to resistance 4, 3
• Do not assume vaccination precludes need for treatment—treat symptomatic patients regardless of vaccination status 1, 2

Supportive Care

• Maintain adequate hydration—consider IV fluids if dehydration present 2
• Oxygen therapy to maintain SaO₂ >92% in children with respiratory distress 2
• Monitor for warning signs requiring immediate attention: difficulty breathing, persistent fever beyond 3-4 days, seizures, altered mental status 2