Daptomycin

Overview

Daptomycin belongs to a distinct antibiotic class of cyclic lipopeptides. In a calcium-dependent manner it inserts its lipophilic tail into the Gram-positive cytoplasmic membrane, oligomerises, and disrupts membrane integrity, causing rapid depolarisation and cell death without lysis. Its unique mechanism means little cross-resistance with other antibiotic classes.

The pivotal randomized trial by Fowler and colleagues established daptomycin 6 mg/kg once daily as non-inferior to standard therapy (vancomycin or an antistaphylococcal penicillin plus gentamicin) for S. aureus bacteraemia and endocarditis, leading to expanded FDA approval.

Daptomycin is inactivated by pulmonary surfactant and therefore must not be used to treat pneumonia. Its main monitorable toxicity is a dose-related rise in creatine phosphokinase with occasional myopathy, so CPK is checked weekly. It is given intravenously once daily, with dose adjustment for renal impairment.

Mechanism of Action

In the presence of physiological calcium, daptomycin's acidic head group and decanoyl tail associate with phosphatidylglycerol-rich regions of the bacterial membrane. Assembly into oligomeric complexes disrupts membrane curvature and fluidity, dissipating the transmembrane potential. Because it does not require intracellular targets or cell entry, killing is rapid and concentration-dependent, favouring once-daily dosing.