Daptomycin is chosen for bacteremia due to vancomycin-resistant Enterococcus. Despite excellent in vitro activity against the organism, it is never used to treat pneumonia. The reason is:

• A Hypoxemia reduces its calcium-dependent bactericidal activity
• B It cannot achieve adequate alveolar penetration because of high protein binding
• C It is rapidly degraded by lung esterases
• D It is inactivated by pulmonary surfactant ✓

Explanation

Daptomycin is a cyclic lipopeptide that inserts into bacterial membranes in a calcium-dependent manner, causing rapid depolarization, potassium efflux, and death without lysis. Pulmonary surfactant binds daptomycin and abolishes its activity, so it fails in pneumonia despite good serum levels. This surfactant antagonism is unique among antibiotics used for Gram-positive bacteremia and makes option B irrelevant to the failure mechanism.

Reference: Katzung Basic and Clinical Pharmacology, 16th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.