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Community-acquired pneumonia with clinically significant drug interactions — ABIM Board MCQ

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HardPharmacologyCommunity-acquired pneumonia with clinically significant drug interactionsABIM Board

A 72-year-old man presents with fever, productive cough, and pleuritic chest pain. Chest radiography shows a new right lower-lobe infiltrate. He is alert, blood pressure is 128/72 mm Hg, respiratory rate is 20/min, and oxygen saturation is 95% on room air. Outpatient treatment is planned. His history includes COPD, stage 3b chronic kidney disease (estimated GFR, 34 mL/min/1.73 m²), gout, and persistent atrial fibrillation. Medications include colchicine 0.6 mg daily and sotalol. ECG shows sinus rhythm with a QTc interval of 510 msec. He has no drug allergies, recent hospitalization, parenteral antibiotic exposure, or prior respiratory isolation of MRSA or Pseudomonas aeruginosa. Which of the following is the most appropriate empiric antibiotic regimen?

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Correct answer: C — Amoxicillin-clavulanate plus doxycycline

This patient has nonsevere community-acquired pneumonia suitable for outpatient treatment but also has chronic lung and renal disease. In outpatients with such comorbidities, recommended regimens include a beta-lactam combined with a macrolide or doxycycline, or respiratory fluoroquinolone monotherapy. Amoxicillin-clavulanate plus doxycycline provides an appropriate regimen while avoiding both major pharmacologic hazards in this case. Clarithromycin inhibits CYP3A4 and P-glycoprotein, the principal pathways governing colchicine disposition. Its concurrent use with colchicine is contraindicated in patients with renal impairment because markedly increased colchicine exposure can cause fatal myelosuppression, neuromyopathy, and multiorgan toxicity. Moxifloxacin and azithromycin can prolong the QT interval and should be avoided in a patient with QTc prolongation who is receiving the class III antiarrhythmic sotalol. Azithromycin monotherapy is additionally inadequate for an outpatient with significant comorbidities. High-dose amoxicillin monotherapy is a guideline option for otherwise healthy outpatients but does not provide the broader empiric regimen recommended here. Thus, the patient's pneumonia severity, comorbidity profile, colchicine interaction, and proarrhythmic risk collectively favor amoxicillin-clavulanate plus doxycycline.

Reference: ATS/IDSA Guidelines for Diagnosis and Treatment of Adults with Community-Acquired Pneumonia (2019) — https://www.idsociety.org/practice-guideline/community-acquired-pneumonia-cap-in-adults Colchicine Capsules Prescribing Information (2023) — https://www.accessdata.fda.gov/drugsatfda_docs/label/2023/204820Orig1s004lbl.pdf FDA Drug Safety Communication: Azithromycin and the Risk of Potentially Fatal Heart Rhythms (2013) — https://www.fda.gov/media/85787/download