A 65-year-old man with COPD presents with fever, dyspnea, and productive cough on day 3 of influenza B illness. He is hospitalized with moderate hypoxemia (SpO₂ 88% on room air). Rapid influenza test confirms influenza B. He has normal renal function. Which antiviral is the drug of choice for severe influenza B?

Explanation

## First-Line Treatment for Severe Influenza B **Key Point:** Oseltamivir remains the gold-standard first-line antiviral for severe influenza B, even in hospitalized patients with moderate-to-severe illness, provided renal function is adequate. ### Why Oseltamivir in Severe Disease? Oseltamivir is the most extensively studied neuraminidase inhibitor with the strongest evidence base for: - Reducing symptom duration and severity - Decreasing risk of secondary bacterial pneumonia - Preventing ICU admission in some cohorts - Efficacy even beyond 48 hours in hospitalized/severe cases ### Dosing in Severe Illness - **Standard:** 75 mg orally twice daily for 5 days - **High-dose option (off-label):** Some centers use 150 mg twice daily in severe/ICU cases, though standard dosing is guideline-recommended - **Renal adjustment:** Mandatory if CrCl < 30 mL/min ### Alternative Antivirals & Their Roles | Agent | Route | Indication | Advantage | Limitation | |-------|-------|-----------|-----------|----------| | **Oseltamivir** | Oral | First-line, all severities | Extensive evidence, both A+B | Requires normal renal function | | Peramivir | IV | Hospitalized, unable to take PO | IV route for severe illness | Limited data; reserved for PO intolerance | | Baloxavir marboxil | Oral | Single-dose convenience | One-time dose | Newer; less data than oseltamivir in severe disease | | Zanamivir | Inhaled | Alternative if PO intolerant | Neuraminidase inhibitor | Bronchospasm risk in COPD (contraindicated here) | **High-Yield:** In hospitalized/severe influenza: 1. **Oseltamivir is still first-line** — most evidence, guideline-endorsed 2. **Peramivir** is reserved for patients unable to take oral medications 3. **Baloxavir** is emerging but has less robust data in severe cases 4. **Zanamivir is contraindicated** in this patient (COPD → bronchospasm risk) **Clinical Pearl:** Even though this patient is on day 3 of illness (beyond the classic 48-hour window), antiviral therapy is strongly recommended in hospitalized/severe cases because it reduces complications and mortality. **Warning:** Do not use zanamivir in COPD patients—inhaled neuraminidase inhibitors carry significant risk of bronchospasm and acute respiratory deterioration. [cite:Harrison 21e Ch 195; CDC Influenza Treatment Guidelines 2023]