NAPLEX Question of the Week: Choose Wisely

This week's question tests your ability within drug selection.
NAPLEX Question of the Week: Choose Wisely

A 65-year-old male patient with a history of hypertension and diabetes mellitus is admitted to the hospital with fever (101.3 F in ED), productive cough, and shortness of breath. A chest X-ray reveals patchy infiltrates in the lower lobe of the right lung. He was recently discharged 3 days prior after a 5-day stay for DKA management.  The patient is diagnosed with pneumonia and started on empiric antibiotic therapy with levofloxacin 750mg IV once daily. However, after 72 hours, his condition does not improve as he continues to have fever and his WBC remains elevated. His renal function is currently within normal limits. His sputum culture (good sample) result reveals the following:

Sputum culture: Staphylococcus aureus (heavy growth 3+)

Amoxicillin   R

Amoxicillin/Clavulanate   R

Ceftriaxone   R

Daptomycin   S

Levofloxacin   R

Linezolid   S

Oxacillin   R

Telavancin   S

Vancomycin   S

Which of the following antibiotics would be appropriate to treat our patient based on this culture result? Select all that apply. 

A) Linezolid

B) Telavancin

C) Nafcillin

D) Vancomycin

E) Daptomycin

Answers with rationale

Pneumonia is a commonly occurring infectious disease and is divided typically into community-acquired, hospital-acquired, and ventilator-associated. While our patient was not in the hospital at the time of the development of symptoms, they were discharged within the previous week, making them a hospital-acquired pneumonia. MRSA and P. aeruginosa are common pathogens within this type of pneumonia and therefore are often covered. Our patient did not respond to initial therapy, most likely because the levofloxacin was not covering the organism. 

Answers A, B, and D are all appropriate treatment for MRSA pneumonia. Vancomycin and linezolid are first-line options for MRSA pneumonia. Linezolid has an oral dosage form, facilitating discharge from hospital easier but caution with thrombocytopenia is advised, especially in durations of 2 weeks or longer.  Telavancin, while FDA-approved for hospital-acquired pneumonia, is rarely used due to its risk of nephrotoxicity. In addition, it is contraindicated in pregnancy, with patients required to have a negative pregnancy test before administering. 

Answer C is incorrect as the oxacillin was resistant therefore this is methicillin-resistant S. aureus, or MRSA. The methicillin resistance can be inferred from the oxacillin result. Nafcillin susceptibility correlates with oxacillin susceptibility and same for resistance and therefore nafcillin would be inappropriate. 

Answer E is incorrect. Daptomycin is a lipopeptide antibiotic with potent bactericidal activity against Gram-positive organisms, including methicillin-resistant Staphylococcus aureus (MRSA). However, it is not indicated for pulmonary infections including pneumonia. This is because daptomycin is deactivated by lung surfactants, which are natural substances present in the alveoli of the lungs that play a crucial role in reducing surface tension and preventing lung collapse during respiration. Daptomycin's mechanism of action involves disrupting the bacterial cell membrane potential, leading to cell death. Unfortunately, the presence of lung surfactants can bind to daptomycin, reducing its effective concentration and rendering it less potent in treating pulmonary infections.

Brand/Generics: Vancomycin (Vancocin), Linezolid (Zyvox, Telavancin (Vibativ), Daptomycin (Cubicin), Oxacillin (Bactocill)

NAPLEX Competencies Covered

  • 2.1 – Pharmacology, mechanism of action, or therapeutic class
  • 3.6 – Drug contraindications, allergies, or precautions

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Go to the profile of Nancy Mekhail
about 1 month ago

Thank you for these great questions.