What is the recommended medical management for a patient with influenza, considering factors such as age, weight, renal function, and underlying medical conditions?

Medical Management of Influenza

Antiviral Treatment Recommendations

For patients with confirmed or suspected influenza, initiate oseltamivir 75 mg orally twice daily for 5 days as soon as possible, ideally within 48 hours of symptom onset, with treatment prioritized for high-risk patients, hospitalized patients, and those with severe illness. 1, 2, 3

Who Should Receive Antiviral Treatment

High-priority patients requiring immediate treatment (regardless of time since symptom onset):

• Hospitalized patients with confirmed or suspected influenza 3
• Severely ill patients with pneumonia, respiratory failure, or progressive illness 4
• Children <2 years of age (highest risk in infants <6 months) 4, 3
• Adults ≥65 years 4, 2
• Pregnant women and postpartum women (within 2 weeks after delivery) 4, 2
• Immunocompromised patients (including those on long-term corticosteroids) 4, 2
• Patients with chronic medical conditions: cardiac disease (except hypertension alone), pulmonary disease (including asthma), renal disease, hepatic disease, diabetes, neurologic disorders, or morbid obesity (BMI ≥40) 4, 2

Standard-risk patients who may benefit from treatment:

• Otherwise healthy outpatients presenting within 48 hours of symptom onset when symptom reduction is desired 1, 2
• Treatment reduces illness duration by 17.6-29.9 hours and decreases pneumonia risk by 50% 1, 3

Critical timing consideration: While greatest benefit occurs within 48 hours, do not withhold treatment from high-risk or severely ill patients presenting beyond 48 hours, as mortality benefit has been demonstrated even with delayed initiation 4, 3

Dosing by Age and Weight

Adults and adolescents ≥13 years:

• 75 mg orally twice daily for 5 days 4, 1, 3

Children 1-12 years (weight-based):

• ≤15 kg: 30 mg twice daily 4, 5
• 15.1-23 kg: 45 mg twice daily 4, 5
• 23.1-40 kg: 60 mg twice daily 4, 5
• >40 kg: 75 mg twice daily 4, 5

Infants <1 year:

• 9-11 months: 3.5 mg/kg twice daily 5
• 0-8 months: 3 mg/kg twice daily 5
• Preterm infants: 1.0-3.0 mg/kg twice daily (based on postmenstrual age) 5

Renal Dose Adjustments

For creatinine clearance <30 mL/min: reduce dose by 50% to 75 mg once daily 4, 3

Detailed renal dosing:

• CrCl >60-90 mL/min: 75 mg twice daily 5
• CrCl >30-60 mL/min: 30 mg twice daily 5
• CrCl >10-30 mL/min: 30 mg once daily 5
• Hemodialysis: 30 mg immediately, then 30 mg after each cycle 5

Alternative Antiviral Agents

When oseltamivir cannot be used:

• Zanamivir (inhaled): 10 mg (two 5-mg inhalations) twice daily for 5 days (approved ≥7 years) 4, 1, 2
• Peramivir (IV): 600 mg single infusion for ages 13-17 years, useful when oral absorption is compromised 1, 2
• Baloxavir (oral): single dose (40 mg for 40-80 kg; 80 mg for ≥80 kg) for patients ≥12 years 1, 2

Do NOT use amantadine or rimantadine due to >99% resistance rates among circulating strains 2, 3

Extended Treatment Duration

Consider longer than 5 days for:

• Immunocompromised patients with persistent viral replication 3
• Critically ill patients with ongoing fever after 6 days 3
• Patients with persistent symptoms despite standard treatment 3

Antibiotic Management

When Antibiotics Are NOT Needed

Previously healthy adults with acute bronchitis complicating influenza (without pneumonia) do NOT routinely require antibiotics 4, 3

When to Add Antibiotics

Consider antibiotics for:

• Previously healthy patients with worsening symptoms (recrudescent fever or increasing dyspnea) 4
• High-risk patients with lower respiratory tract features 4
• Patients not improving after 3-5 days of antiviral treatment 2, 3
• Clinical deterioration at any point suggesting bacterial co-infection 2, 3

Antibiotic Selection

For non-severe pneumonia (oral therapy):

• First choice: co-amoxiclav or tetracycline 4, 3
• Alternative: clarithromycin or fluoroquinolone (active against S. pneumoniae and S. aureus) 4

Pediatric antibiotic dosing:

• Co-amoxiclav 1-12 months: 2.5 mL three times daily (125/31 suspension) 4
• Co-amoxiclav 1-6 years: 5 mL three times daily (125/31 suspension) 4
• Co-amoxiclav 7-12 years: 5 mL three times daily (250/62 suspension) 4

For severe pneumonia requiring hospitalization:

• IV combination therapy with broad-spectrum β-lactamase stable antibiotic plus macrolide 3
• Antibiotics should be administered within 4 hours of admission 3

Supportive Care

Essential supportive measures:

• Oxygen therapy to maintain PaO₂ ≥8 kPa and SaO₂ ≥92% 4
• Adequate hydration and rest 1, 2
• Antipyretics (acetaminophen or ibuprofen) for fever and myalgias 1, 2
• Avoid aspirin in patients <19 years due to Reye's syndrome risk 1
• Nutritional support in severe or prolonged illness 4

Do NOT use corticosteroids for influenza treatment unless clinically indicated for other reasons, as they increase mortality risk and bacterial superinfection 2, 6

Monitoring and Follow-Up

Monitor vital signs at least twice daily:

• Temperature, respiratory rate, pulse, blood pressure, mental status, oxygen saturation 4

Patients should show clinical improvement within 48 hours of starting antivirals 2

Reassess if:

• Fever persists beyond 4-5 days without improvement 2
• Clinical deterioration occurs at any point 2
• No improvement after 3-5 days of treatment 2, 3

Discharge criteria - patients should NOT have ≥2 of the following:

• Temperature >37.8°C 4
• Heart rate >100/min 4
• Respiratory rate >24/min 4
• Systolic blood pressure <90 mmHg 4
• Oxygen saturation <90% 4
• Inability to maintain oral intake 4
• Abnormal mental status 4

Common Pitfalls to Avoid

Do NOT delay treatment while awaiting laboratory confirmation in high-risk or severely ill patients 4, 1, 3

Do NOT withhold treatment based solely on time since symptom onset if the patient has moderate-to-severe illness or high-risk features 1, 3

Take oseltamivir with food to reduce gastrointestinal side effects (nausea/vomiting occur in ~10-15% of patients) 3

Do NOT use zanamivir dry powder via nebulization in intubated patients, as it causes ventilator malfunction 6

Neuropsychiatric events have not been definitively linked to oseltamivir and should not prevent appropriate treatment 3