A 38-year-old woman from Delhi presents to the emergency department with a 3-day history of high fever (39.5°C), myalgia, headache, and dry cough. She reports sudden onset of illness after exposure to her colleague who had similar symptoms 2 days ago. On examination, she has pharyngeal erythema and bilateral crackles on auscultation. Rapid influenza diagnostic test (RIDT) is positive. Chest X-ray shows patchy infiltrates in the left lower lobe. Which of the following antivirals is most effective if initiated within 48 hours of symptom onset?

Explanation

## Management of Influenza: Antiviral Therapy **Key Point:** Oseltamivir is the first-line neuraminidase inhibitor for treatment of influenza A and B, with maximum benefit when started within 48 hours of symptom onset. ### Mechanism of Action Neuraminidase inhibitors block the release of progeny virions from infected cells by inhibiting the viral neuraminidase enzyme, which cleaves sialic acid receptors on the cell surface. ### Efficacy in Clinical Practice | Antiviral | Class | Indication | Timing | Efficacy | |-----------|-------|-----------|--------|----------| | **Oseltamivir** | Neuraminidase inhibitor | Treatment & prophylaxis | Within 48 hrs | Reduces symptom duration by ~1 day; prevents complications | | Zanamivir | Neuraminidase inhibitor | Treatment & prophylaxis | Within 48 hrs | Similar efficacy to oseltamivir; inhaled route | | Amantadine | M2 channel blocker | Treatment (A only) | Early | High resistance rates (>90%); rarely used now | | Ribavirin | Nucleoside analog | Severe/immunocompromised | Any time | Limited evidence; not standard | **High-Yield:** Oseltamivir is the **gold standard** for influenza treatment because: 1. Effective against both influenza A and B 2. Oral bioavailability (convenient dosing) 3. Reduces duration of illness by ~24 hours 4. Decreases risk of secondary bacterial pneumonia and hospitalization 5. Low resistance rates compared to adamantanes **Clinical Pearl:** In this patient with fever, myalgia, and lower lobe infiltrates suggesting early pneumonia, oseltamivir initiated within 48 hours can reduce progression to severe disease and secondary bacterial superinfection. ### Why Oseltamivir Over Zanamivir? - Both are neuraminidase inhibitors with similar efficacy - Oseltamivir: oral, better GI absorption, standard first-line - Zanamivir: inhaled, risk of bronchospasm in asthmatics (this patient has respiratory involvement) **Tip:** Remember the "48-hour window"—antivirals must be started within 2 days of symptom onset for maximum clinical benefit. [cite:Harrison 21e Ch 195]