Long-circulating liposomal daptomycin enhances protection against systemic methicillin-resistant Staphylococcus aureus infection with improved therapeutic potential.

In the face of escalating problems with pathogen control, the development of proper formulations of existing antibiotics is as important as the development of novel antibiotics. Daptomycin is a lipopeptide antibiotic with potent activity against Gram-positive bacteria. Currently, only injectable solution of daptomycin has been approved for clinical use. In the present study, the formulation of PEGylated liposomal daptomycin (PLD) was prepared and optimized, and its efficacy against methicillin-resistant Staphylococcus aureus (MRSA252) strains was investigated. The obtained PLD had a mean vesicle diameter of (111.5 +/- 15.4) nm and a mean percent drug loading of (5.81 +/- 0.19) % with high storage stability. Potent activity of PLD against MRSA was demonstrated in vitro with a more sustained effect than that of conventional liposomal daptomycin and daptomycin solution. In addition, intravenous administration of a single dose (equal to human use) of PLD significantly increased the survival of mice in a MRSA252 systemic infection model compared with other formulations. Drug distribution in the lung was significantly enhanced following administration of PLD, and no measurable tissue lesions or pathological changes were detected during PLD treatment. Taken together, PEGylated liposomes loaded with daptomycin may represent a promising approach to reduce MRSA252 infections, especially those involving bloodstream dissemination, such as hematogenous pulmonary infection.