How should I treat influenza (flu) in an adult, including supportive care and antiviral therapy?

How to Treat Influenza (Flu)

Start oseltamivir 75 mg orally twice daily for 5 days if the patient presents within 48 hours of symptom onset with fever >38°C, combined with supportive care including acetaminophen for fever and body aches. 1, 2

Antiviral Therapy: Oseltamivir

When to Initiate Treatment

• Prescribe oseltamivir for all patients who meet these three criteria: 3, 1

  • Acute influenza-like illness (fever, cough, myalgias, malaise)
  • Fever >38°C in adults (>38.5°C in children)
  • Symptom duration ≤48 hours

• Standard adult dosing: 75 mg orally twice daily for 5 days 3, 1

• Renal dose adjustment: Reduce to 75 mg once daily if creatinine clearance <30 mL/min 3, 1

Extended Window for High-Risk Patients

• Treat beyond 48 hours if the patient has any high-risk features, as mortality benefit persists up to 96 hours: 2, 4

  • Age <2 years or ≥65 years
  • Pregnancy or postpartum period
  • Immunocompromised status
  • Chronic cardiac, pulmonary, renal, hepatic, neurologic, or metabolic disease
  • Severe illness requiring hospitalization
  • Evidence of complications (e.g., pneumonia)

• Special consideration: Patients unable to mount adequate fever response (immunocompromised, very elderly) may still qualify for treatment despite lack of documented fever 3

Expected Benefits

• Reduces illness duration by approximately 24 hours 3, 5
• May reduce hospitalization risk 3
• Decreases subsequent antibiotic use 3
• Note: Evidence does not definitively prove mortality reduction in otherwise healthy adults, but benefit is established in high-risk groups 3, 2

Common Side Effects

• Nausea occurs in ~10% of patients; manage with mild anti-emetics 3

Symptomatic Management

Fever and Body Aches

• First-line: Acetaminophen (paracetamol) for fever and myalgias based on favorable safety profile 2
• Alternative: Ibuprofen (use with caution) 2
• Goal: Alleviate distressing symptoms, not solely reduce temperature 2
• Contraindication: Never use aspirin in children <16 years due to Reye's syndrome risk 2, 4

Additional Supportive Measures

• Rest and adequate hydration (but no more than 2 liters per day) 2
• Avoid smoking 2
• Short-term topical decongestants, throat lozenges, or saline nose drops as needed 2
• For distressing cough: consider codeine linctus, codeine phosphate tablets, or morphine sulfate oral solution 2
• For children >1 year with cough: honey can be used as a simple remedy 2

Antibiotic Use: Critical Decision Points

When NOT to Prescribe Antibiotics

• Do not routinely prescribe for previously healthy adults with uncomplicated influenza or acute bronchitis without pneumonia 3, 2
• Antibiotics are not indicated for isolated viral influenza symptoms 4, 6

When TO Prescribe Antibiotics

Initiate antibiotics if the patient develops: 3, 2

• Recrudescent fever (fever returning after initial improvement)
• Worsening dyspnea after initial improvement
• Lower respiratory tract involvement in high-risk individuals
• Radiographically confirmed pneumonia

Antibiotic Selection

For non-severe pneumonia or bronchitis with bacterial features: 3, 2

• First-line oral: Co-amoxiclav or tetracycline (e.g., doxycycline)
• Alternative: Macrolide (clarithromycin or erythromycin) or respiratory fluoroquinolone (levofloxacin, moxifloxacin)

For severe influenza-related pneumonia: 3, 6

• Intravenous combination: Co-amoxiclav or cephalosporin (cefuroxime or cefotaxime) PLUS macrolide (clarithromycin or erythromycin)
• Alternative: Respiratory fluoroquinolone with activity against S. pneumoniae and S. aureus
• Administer within 4 hours of admission 3

Duration of Antibiotic Therapy

• Uncomplicated pneumonia: 7 days 2, 6
• Severe pneumonia or suspected S. aureus: 10-14 days 2, 6

Monitoring and Red Flags

When to Seek Immediate Medical Attention

Instruct patients to return immediately if they develop: 2, 4, 6

• Shortness of breath at rest or with minimal activity
• Painful or difficult breathing
• Coughing up bloody sputum (hemoptysis)
• Drowsiness, disorientation, or confusion
• Fever persisting 4-5 days without improvement
• Initial improvement followed by recurrence of high fever

Hospitalization Criteria

Admit if ANY TWO of the following are present: 3, 2

• Temperature >37.8°C
• Heart rate >100 beats/min
• Respiratory rate >24 breaths/min
• Systolic blood pressure <90 mmHg
• Oxygen saturation <90% on room air
• Inability to maintain oral intake
• Altered mental status

In-Hospital Monitoring

• Record vital signs (temperature, respiratory rate, pulse, blood pressure, oxygen saturation, mental status) at least twice daily, more frequently if critically ill 3, 2

Common Pitfalls to Avoid

• Do not withhold oseltamivir from high-risk patients based solely on timing beyond 48 hours—mortality benefit persists up to 96 hours 2, 4
• Do not prescribe antibiotics reflexively for viral symptoms alone; this drives antibiotic resistance 4
• Do not delay antibiotics when bacterial superinfection is clinically evident (worsening at day 4-5, new respiratory findings) 2, 6
• Do not allow return to work while febrile; patients remain contagious 2
• Do not use aspirin in children or adolescents <16 years 2, 4

Special Populations

Pediatric Dosing (Oseltamivir)

• Age 1-9 years: 5 mg/kg/day divided twice daily (not to exceed 150 mg/day) 3
• Age ≥10 years: 75 mg twice daily 3
• Weight-based dosing for children 1-12 years: 1
  • ≤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

Pregnancy and Immunocompromised Patients

• Treat with oseltamivir even if evidence is limited, as these are high-risk groups 2, 7
• Immunocompromised patients may receive prophylaxis for up to 12 weeks during outbreaks 1

Infection Control

• Advise hand hygiene and respiratory etiquette 4
• Consider post-exposure prophylaxis with oseltamivir 75 mg once daily for 10 days for high-risk household contacts 4