What is the recommended treatment for an adult patient diagnosed with influenza?

Treatment of Influenza in Adults

For adults diagnosed with influenza, initiate oseltamivir 75 mg orally twice daily for 5 days, ideally within 48 hours of symptom onset, though treatment should not be withheld in severely ill, hospitalized, or high-risk patients presenting beyond this window. 1, 2, 3

Antiviral Therapy: Oseltamivir (Tamiflu)

Standard Dosing and Administration

• Oseltamivir 75 mg orally twice daily for 5 days is the treatment of choice for confirmed or suspected influenza in adults and adolescents ≥13 years. 1, 3
• Taking oseltamivir with food enhances tolerability and reduces nausea, which occurs in approximately 10-15% of patients compared to 9% with placebo. 1, 4, 5
• The medication may be taken with or without food, but tolerability is enhanced when taken with food. 3

Timing of Treatment Initiation

• Maximum benefit occurs when treatment starts within 48 hours of symptom onset, reducing illness duration by 24-36 hours (approximately 1-1.5 days) and symptom severity by 30-38%. 1, 4, 6
• Earlier initiation within 24 hours provides even greater benefit, reducing illness duration by 43-47 hours (37-40% reduction) compared to placebo. 6
• Treatment initiated within 12 hours of symptom onset provides an additional 74.6 hours of benefit compared to treatment at 48 hours. 5

Critical Exceptions: Treatment Beyond 48 Hours

Do not withhold oseltamivir in the following populations, even if presenting beyond 48 hours: 1, 2, 7

• Hospitalized patients who are severely ill - these patients demonstrate significant mortality benefit (OR = 0.21 for death within 15 days) even when treatment is initiated up to 96 hours after symptom onset. 1, 7
• High-risk populations, including:
  • Adults ≥65 years of age 1, 2
  • Pregnant women 1
  • Immunocompromised patients (including those on long-term corticosteroids, chemotherapy, transplant recipients) 1, 7
  • Chronic respiratory disease (COPD, asthma, bronchiectasis) 1, 8, 9
  • Chronic cardiac disease 1, 8, 9
  • Diabetes mellitus requiring medication 1
  • Chronic renal or liver disease 1
• Patients with severe or progressive illness at any point in their disease course 1, 2
• Elderly or immunocompromised patients who cannot mount adequate febrile response despite lack of documented fever 1, 7

Renal Dose Adjustment

• Reduce dose to 75 mg once daily if creatinine clearance is <30 mL/min. 1, 3
• For creatinine clearance 10-30 mL/min during prophylaxis, use 30 mg once daily or 75 mg every other day. 1

Expected Clinical Benefits

Symptom Reduction

• Reduces illness duration by 29-35 hours (25-30% reduction) when initiated within 36 hours of symptom onset. 6
• Decreases symptom severity by up to 38% compared to placebo. 4
• Reduces duration of troublesome symptoms: fatigue by 29% and myalgia by 26%. 8
• Shortens median duration of acute febrile illness, particularly in patients with cardiac disease (44.0 vs 64.7 hours) or COPD (37.9 vs 53.8 hours). 8

Complication Prevention

• Reduces risk of pneumonia by 50% in patients with laboratory-confirmed influenza. 1, 7
• Decreases secondary complications requiring antibiotics by 35%. 1
• Reduces antibiotic use by 32-37% in high-risk patients. 8, 9
• Lowers incidence of complications from 45% to 11% in high-risk populations. 9

Mortality Benefit

• Significantly decreases risk of death within 15 days of hospitalization (OR = 0.21) in high-risk and hospitalized patients, even when treatment is initiated >48 hours after symptom onset. 1, 7

Functional Recovery

• Accelerates return to normal health status, usual activities, and normal sleep patterns compared to placebo. 4, 8
• Reduces viral shedding quantity and duration, though complete cessation is not guaranteed. 4

Alternative Antiviral Options

• Zanamivir (10 mg inhaled twice daily for 5 days) may be considered as an alternative, but should be avoided in patients with underlying airways disease (asthma, COPD) due to bronchospasm risk. 1, 2
• Baloxavir (single oral dose) may be considered as an alternative, though oseltamivir remains first-line due to established efficacy. 2

Antibiotic Considerations

When Antibiotics Are NOT Indicated

• Antibiotics are NOT routinely indicated for uncomplicated influenza in previously healthy adults. 1
• Do not reflexively add antibiotics for viral influenza symptoms alone, as this contributes to resistance. 1

When to Add Antibiotics

Consider antibiotics in the following scenarios: 1, 2

• Patients with COPD or other severe pre-existing illnesses should receive antibiotics empirically. 1
• Previously well patients with worsening symptoms after initial improvement, particularly:
  • Recrudescent fever 1, 2
  • Increasing breathlessness 1, 2
• Clinical evidence of bacterial pneumonia on examination 1
• New consolidation on chest imaging 1
• Purulent sputum production 1
• Elevated inflammatory markers suggesting bacterial infection 1

First-Line Antibiotic Choices

• Co-amoxiclav (amoxicillin-clavulanate), doxycycline, or cefuroxime/cefotaxime to cover Streptococcus pneumoniae, Staphylococcus aureus (including MRSA), and Haemophilus influenzae. 1, 2
• For severe pneumonia: IV co-amoxiclav or cephalosporin PLUS macrolide (clarithromycin preferred over azithromycin for better H. influenzae activity). 1
• Antibiotics should be administered within 4 hours if pneumonia is confirmed on admission. 2

Risk Stratification and Hospitalization Criteria

CRB-65 Score Assessment

• Calculate CRB-65 score for patients with suspected influenza-related pneumonia: 1
  • Confusion: 1 point
  • Respiratory rate ≥30/min: 1 point
  • Blood pressure (SBP <90 or DBP ≤60 mmHg): 1 point
  • Age ≥65 years: 1 point

Hospitalization Indications

• Consider hospital referral for CRB-65 score of 1-2; urgent admission for score ≥3. 1
• Bilateral chest signs of pneumonia warrant hospital referral regardless of CRB-65 score. 1
• Consider hospitalization if ≥2 of the following are present: temperature >37.8°C, heart rate >100/min, respiratory rate >24/min, systolic BP <90 mmHg, oxygen saturation <90%, inability to maintain oral intake, or altered mental status. 2

Common Pitfalls to Avoid

• Do not withhold treatment beyond 48 hours in severely ill, hospitalized, or high-risk patients - multiple studies demonstrate mortality benefit when treatment is initiated up to 96 hours after symptom onset. 1, 7
• Do not wait for laboratory confirmation before initiating therapy in high-risk patients - rapid tests have poor sensitivity, and negative results should not exclude treatment during influenza season. 1, 7
• Do not use double-dose oseltamivir (150 mg twice daily) - no additional benefit has been demonstrated. 1
• Do not prescribe zanamivir to patients with asthma or COPD due to bronchospasm risk. 1
• Do not reflexively add antibiotics for uncomplicated viral influenza - reserve antibiotics for evidence of bacterial superinfection. 1

Adverse Effects and Safety

• Most common adverse effects are nausea (10-15%) and vomiting (15% vs 9% placebo), which are typically mild, transient, and resolve within 1-2 days. 1, 4, 5
• Taking oseltamivir with food significantly reduces gastrointestinal side effects. 3, 4, 5
• No established link between oseltamivir and neuropsychiatric events has been confirmed. 1
• Gastrointestinal events rarely result in study discontinuation. 4, 8

Prophylaxis Considerations

• Post-exposure prophylaxis: 75 mg once daily for 10 days following close contact with an infected individual, initiated within 48 hours of exposure. 3
• Seasonal prophylaxis: 75 mg once daily for up to 6 weeks during community outbreak. 3
• Immunocompromised patients may continue prophylaxis for up to 12 weeks. 3
• Prophylaxis efficacy ranges from 58.5-89% when started within 48 hours of household exposure. 1
• Prophylaxis is not a substitute for annual vaccination, which remains the primary prevention strategy. 1