Why is daptomycin not effective for pneumonia?

• A. It is inactivated by kidney disease
• B. It has poor Gram-positive activity
• C. It is rapidly excreted renally
• D. It is inactivated by pulmonary surfactant

Answer: (C)

Daptomycin is ineffective for pneumonia because it is inactivated by pulmonary surfactant. When it reaches the alveoli, surfactant binds and inactivates the drug, preventing it from disrupting bacterial cell membranes where the infection is located. So, despite good systemic levels and activity against Gram-positive organisms, daptomycin cannot exert its effect in the lungs. The fact that it is cleared renally is a separate pharmacokinetic detail and does not explain the lack of efficacy in pneumonia.