A 38-year-old woman presents to the emergency department with fever (38.9°C), cough, myalgia, and headache for 2 days. Rapid influenza diagnostic test is positive for influenza A. She has no contraindications to antivirals. What is the drug of choice for treatment of acute influenza infection?

Explanation

## First-Line Antiviral for Influenza **Key Point:** Oseltamivir (Tamiflu) is the preferred first-line neuraminidase inhibitor for treatment of acute influenza A and B infections. ### Mechanism of Action Neuraminidase inhibitors block viral neuraminidase, preventing release of progeny virions from infected cells. Oseltamivir is a prodrug that is converted to its active form (oseltamivir carboxylate) by hepatic esterases. ### Dosing & Timing - **Dose:** 75 mg orally twice daily for 5 days - **Critical:** Must be initiated within **48 hours of symptom onset** for maximum efficacy - Reduces symptom duration by ~1 day and decreases complications in high-risk patients ### Why Oseltamivir Over Other Antivirals | Feature | Oseltamivir | Amantadine/Rimantadine | Zanamivir | |---------|-------------|------------------------|----------| | **Spectrum** | Influenza A + B | Influenza A only | Influenza A + B | | **Route** | Oral (convenient) | Oral | Inhaled | | **Resistance** | Lower rates | High resistance now | Lower rates | | **Tolerability** | GI upset common | CNS effects (elderly) | Bronchospasm risk | | **First-line status** | YES | No (obsolete) | Alternative | **High-Yield:** Amantadine and rimantadine are M2 inhibitors with **high rates of resistance** (>50% in many regions) and are no longer recommended as first-line agents. They also cause CNS side effects (tremor, confusion, hallucinations) especially in elderly patients. **Clinical Pearl:** Zanamivir is an acceptable alternative but is inhaled and carries risk of bronchospasm in patients with underlying airway disease (asthma, COPD). Oseltamivir is oral and better tolerated overall. ### High-Risk Patients Requiring Treatment - Pregnant women - Age ≥65 years - Chronic medical conditions (diabetes, heart disease, lung disease) - Immunocompromised - Severe or progressive illness **Warning:** Do NOT delay treatment waiting for confirmatory testing. Clinical diagnosis + high suspicion in an epidemic setting warrants immediate oseltamivir initiation.