Why is daptomycin not used for pneumonia and what is its primary spectrum?

• A. Inactivated by pulmonary surfactant; active against Gram-positive organisms including MRSA and VRE.
• B. Resistant to surfactant; active against Gram-negative organisms only.
• C. Efficient in pneumonia but not in skin infections; active against anaerobes.
• D. Inactivated by alveolar macrophages; broad-spectrum including Gram-negatives.

Answer: (A)

Daptomycin works by binding to Gram-positive bacterial membranes in a calcium-dependent way, causing rapid membrane depolarization and cell death. However, in the lungs, pulmonary surfactant binds and inactivates daptomycin, so it cannot reach effective concentrations at the site of infection in the alveoli. Because of this inactivation by surfactant, daptomycin is not used for pneumonia. Its spectrum is limited to Gram-positive organisms, including MRSA and VRE, with little to no activity against Gram-negative bacteria.