Community-acquired pneumonia
USMLE Step 2 CKDifficulty: mediumLast updated:
A 34-year-old man presents with 3 days of fever, productive cough, and right-sided pleuritic chest pain. He has no chronic medical conditions, takes no medications, has not received antibiotics or been hospitalized in the past year, and does not smoke. He is alert and oriented. Temperature is 38.6°C (101.5°F), blood pressure 126/78 mm Hg, pulse 98/min, respirations 20/min, and oxygen saturation 96% on room air. BUN is 12 mg/dL. Chest x-ray shows right lower lobe consolidation. He is to be treated as an outpatient.
According to ATS/IDSA guidance, which of the following is the most appropriate antibiotic regimen?
Answer and explanation
Correct answer: C. Amoxicillin 1 g orally three times daily
This is a previously healthy outpatient with community-acquired pneumonia, no comorbidities, and no risk factors for resistant pathogens. His CURB-65 score is 0: he is not confused, BUN is not > 19 mg/dL, respiratory rate is < 30/min, blood pressure is normal, and he is younger than 65. The 2019 ATS/IDSA guideline recommends, for healthy outpatient adults without comorbidities, amoxicillin 1 g three times daily as a strong recommendation. Doxycycline is a conditional alternative, and a macrolide is an option only where pneumococcal macrolide resistance is < 25%. Combination therapy with amoxicillin-clavulanate or a cephalosporin plus a macrolide or doxycycline, or monotherapy with a respiratory fluoroquinolone, is reserved for outpatients with comorbidities such as chronic heart, lung, liver, or renal disease, diabetes, alcoholism, malignancy, or asplenia. IV regimens are for hospitalized patients.
Each option explained
- A. IV ceftriaxone plus IV azithromycinIncorrect. IV ceftriaxone plus azithromycin is a regimen for hospitalized (non-ICU) patients.
- B. IV vancomycin plus piperacillin-tazobactamIncorrect. Anti-MRSA and antipseudomonal coverage is reserved for inpatients with specific risk factors.
- C. Amoxicillin 1 g orally three times dailyCorrect. Amoxicillin 1 g three times daily is the strongly recommended regimen for healthy outpatients without comorbidities.
- D. Levofloxacin 750 mg orally once dailyIncorrect. Respiratory fluoroquinolone monotherapy is reserved for outpatients with comorbidities, to limit adverse effects and resistance.
- E. Amoxicillin-clavulanate plus azithromycin orallyIncorrect. Beta-lactam plus macrolide combination therapy is recommended for outpatients with comorbidities.
Key point
For healthy adult outpatients with CAP, ATS/IDSA 2019 recommends amoxicillin 1 g three times daily (doxycycline as an alternative).
From the source
“For patients without comorbidities that increase the risk for poor outcomes, the panel recommended amoxicillin 1 g every 8 hours or doxycycline 100 mg twice daily.”