What is the recommended treatment for adults with influenza?

Influenza Treatment in Adults: Clinical Algorithm

For adults with confirmed or suspected influenza, initiate oseltamivir 75 mg orally twice daily for 5 days, ideally within 48 hours of symptom onset, though treatment should still be offered to severely ill, hospitalized, or high-risk patients regardless of illness duration. 1, 2, 3

Initial Assessment and Risk Stratification

Determine Treatment Eligibility

• Symptom onset timing: Treatment is most effective when started within 48 hours of symptom onset, ideally within 24 hours 3, 4, 5
• Severity assessment: Evaluate for severe illness indicators including respiratory distress (respiratory rate >30/min), hypoxia (oxygen saturation <90%), hemodynamic instability (systolic blood pressure <90 mmHg, heart rate >100/min), or altered mental status 1, 6
• High-risk conditions: Identify patients with age ≥65 years, chronic cardiac or pulmonary disease (including COPD), diabetes, immunosuppression, obesity (BMI ≥30), pregnancy, or other chronic medical conditions 1, 2

Treatment Decision Algorithm

Step 1: Is the patient within 48 hours of symptom onset?

• YES → Proceed to Step 2
• NO → Proceed to Step 3

Step 2: For patients within 48 hours

• All patients with confirmed or suspected influenza: Prescribe oseltamivir 75 mg orally twice daily for 5 days 3, 7
• Dosing: Take with food to reduce nausea (occurs in ~10% of patients) 2, 4
• Expected benefit: Reduces illness duration by 24-36 hours (up to 43-47 hours if started within 24 hours) 1, 7, 5

Step 3: For patients beyond 48 hours

• Hospitalized or severely ill patients: Prescribe oseltamivir regardless of illness duration 1, 2
• High-risk patients (age ≥65, chronic disease, immunocompromised, pregnant): Prescribe oseltamivir even beyond 48 hours 2
• Otherwise healthy outpatients: Antiviral treatment provides minimal benefit; focus on supportive care 2, 8

Antiviral Therapy Details

Oseltamivir (First-Line Agent)

• Standard dose: 75 mg orally twice daily for 5 days 3, 7
• Renal adjustment: Reduce to 75 mg once daily if creatinine clearance <30 mL/min 2, 3
• Administration: May be taken with or without food, though food enhances tolerability 3, 4
• Adverse effects: Nausea (10-15%) and vomiting (15% vs 9% placebo), typically mild and transient 9, 7, 4

Alternative Agents (When Oseltamivir Unavailable or Contraindicated)

• Zanamivir: 10 mg (2 inhalations) twice daily for 5 days; avoid in patients with underlying airways disease (asthma, COPD) 9
• Baloxavir: Single oral dose alternative, though oseltamivir remains first-line due to established efficacy 1

Antibiotic Considerations

When Antibiotics Are NOT Indicated

• Uncomplicated influenza in previously healthy adults without evidence of bacterial superinfection 2, 6
• Acute bronchitis from influenza alone does not warrant antibiotics 6

When to Consider Antibiotics

• Bacterial superinfection suspected: Worsening symptoms after initial improvement, recrudescent fever, or increasing breathlessness 1, 2, 6
• Pre-existing severe illness: Patients with COPD or other severe chronic conditions should receive empiric antibiotics 2
• Confirmed pneumonia: Clinical or radiographic evidence of bacterial pneumonia 2
• First-line choices: Co-amoxiclav (amoxicillin-clavulanate), doxycycline, or cefuroxime to cover Streptococcus pneumoniae, Staphylococcus aureus (including MRSA), and Haemophilus influenzae 1, 2
• Timing: Administer within 4 hours if pneumonia confirmed on admission 1

Monitoring and Follow-Up

Expected Clinical Course

• Typical fever duration: 3-5 days in uncomplicated cases 1
• Total illness duration: Usually resolves within 7 days, though cough, malaise, and fatigue may persist for weeks 6
• Antiviral effect: Reduces symptom duration by approximately 1 day when started early 9, 7, 5

Red Flag Symptoms Requiring Urgent Evaluation

• Respiratory: Increasing shortness of breath, respiratory rate >30/min, oxygen saturation <90% 1, 6
• Hemodynamic: Heart rate >100/min, systolic blood pressure <90 mmHg 1, 6
• Neurological: Altered mental status, confusion, drowsiness 1, 6
• Prolonged fever: Temperature >37.8°C lasting more than 4-6 days suggests complications 1, 6
• Worsening after improvement: Recrudescent fever or increasing dyspnea suggests bacterial superinfection 1, 2, 6

Hospitalization Criteria

• CRB-65 score ≥1-2: Consider hospital referral; urgent admission if ≥3 2
  • Confusion (1 point)
  • Respiratory rate ≥30/min (1 point)
  • Blood pressure: SBP <90 or DBP ≤60 mmHg (1 point)
  • Age ≥65 years (1 point)
• Bilateral pneumonia: Warrants hospital referral regardless of score 2
• Severe illness indicators: Hypoxia, hemodynamic instability, inability to maintain oral intake, or altered mental status 1, 6

Special Populations

Pregnant Women

• Treatment: Oseltamivir should be given to pregnant women with influenza, as they are at high risk of complications 2
• Timing: Treat even beyond 48 hours if high-risk 2

Immunocompromised Patients

• Extended treatment: May require longer than 5-day course 9
• Prophylaxis duration: May continue up to 12 weeks during outbreaks 3
• Treatment threshold: Lower threshold for initiating antivirals, even beyond 48 hours 2

Elderly Patients (≥65 years)

• Automatic high-risk: Treat even beyond 48 hours 1, 2
• Atypical presentation: May present without fever 1
• Increased complications: Higher risk of hospitalization and death 9, 10

Infection Control Measures

Patient Education

• Hand hygiene: Strict handwashing or alcohol-based hand sanitizer, especially after coughing or sneezing 6
• Respiratory etiquette: Cover coughs/sneezes with tissue or sleeve (not hands), dispose of tissues immediately 6
• Isolation: Avoid contact with others, especially high-risk individuals, until fever-free for 24 hours without antipyretics 6
• Work/school exclusion: Remain off work while symptomatic 6

Common Pitfalls to Avoid

Antiviral Prescribing Errors

• Don't withhold treatment beyond 48 hours in severely ill, hospitalized, or high-risk patients—these populations may still benefit 1, 2
• Don't use double-dose oseltamivir (150 mg twice daily)—no additional benefit demonstrated 9
• Don't prescribe zanamivir to patients with asthma or COPD due to bronchospasm risk 9

Antibiotic Misuse

• Don't routinely prescribe antibiotics for uncomplicated influenza in healthy adults 2, 6
• Don't delay antibiotics if bacterial superinfection is suspected—empiric coverage should be started promptly 1, 2

Monitoring Failures

• Don't dismiss prolonged fever (>4-6 days) as normal—evaluate for complications 1, 6
• Don't ignore worsening after initial improvement—this pattern strongly suggests bacterial superinfection 1, 2, 6