Daptomycin is used for complicated skin infections and bacteraemia caused by MRSA. It is NOT used for pneumococcal pneumonia because:

• A It cannot cross the blood-air barrier and achieve minimum inhibitory concentrations in alveolar fluid
• B It is inactivated by pulmonary surfactant (phosphatidylglycerol), preventing adequate lung tissue levels ✓
• C Streptococcus pneumoniae has intrinsic resistance to daptomycin via its thick capsule
• D Daptomycin is hepatically metabolised and undergoes extensive biliary excretion before reaching lung tissue

Explanation

Daptomycin is a cyclic lipopeptide that inserts into bacterial membranes and causes rapid depolarisation. In the lung, pulmonary surfactant contains abundant phosphatidylglycerol, which binds and sequesters daptomycin, rendering it inactive in alveolar spaces. Clinical trials confirmed its inferiority in pneumonia despite in vitro S. aureus activity. It remains highly effective for bacteraemia and endocarditis where surfactant is absent.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.