Legionella Pneumonia — FRCA Final MCQ
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Correct answer: C — Clarithromycin
Clarithromycin is the correct answer. Legionella pneumophila replicates intracellularly, so treatment requires an agent with reliable intracellular activity. Clarithromycin is a macrolide that penetrates lung tissue and inhibits bacterial protein synthesis through binding to the 50S ribosomal subunit; the UK intravenous clarithromycin SmPC lists community-acquired pneumonia as an indication and Legionella species as commonly susceptible organisms. Amoxicillin, co-amoxiclav and ceftriaxone may form part of empirical treatment for severe pneumonia but do not provide reliable directed anti-Legionella activity. Flucloxacillin is primarily used for susceptible staphylococcal infection. In a critically ill patient, clarithromycin may initially be administered intravenously, with subsequent route and duration guided by clinical response and specialist microbiological advice.
Reference: electronic Medicines Compendium. Clarithromycin 500 mg powder for concentrate for solution for infusion, Summary of Product Characteristics, sections 4.1 and 5.1. Updated 5 August 2026. https://www.medicines.org.uk/emc/product/9235/smpc