Amikacin liposomes: characterization, aerosolization, and in vitro activity against Mycobacterium avium-intracellulare in alveolar macrophages

Abstract

A feasible way to treat pulmonary Myobacterium avium-intracellulare (MAI) infections is inhalation of liposome-encapsulated antimycobacterial agents aimed at infected alveolar macrophages (AM). To this end, amikacin-containing liposomes consisting of soy phosphatidylcholine (SPC), hydrogenated SPC (HSPC) and phosphatidylglycerol (PG) or cholesterol (CH) were prepared by extrusion and characterized with respect to drug content, encapsulation efficiency, drug retention in lung lavage fluid, stability during aerosolization, and in vitro efficacy against MAI in murine AM. Unencapsulated amikacin was separated by dialysis and ion-exchanged (Amberlite IRC50) adsorption which was found to be fast, complete and less cumbersome than dialysis. Drug content increased linearly with drug concentration for a fixed lipid concentration from 1 to 12% for SPC, and from 5 to 21% for SPC/PG (7:3 molar ratio) liposomes, while the amikacin content remained constant at 0.5–1% (SPC) and 1.5–2% (SPC/PG) over a lipid concentration range of 20–160 mg/ml for a fixed amikacin concentration. With increasing lipid concentration (10–160 mg/ml), the encapsulation efficiency increased linearly for SPC liposomes (2–20%), and in a saturable fashion for SPC/PG liposomes (1–35%). Aerosolization (Collison nebulizer) over 80 min resulted in loss of content of approx. 20% (SPC and HSPC) and 30–40% (SPC/PG and SPC/CH), respectively. Incubation with fresh lung lavage fluid at 37°C resulted in poor retention of amikacin in SPC/PG liposomes, whereas SPC and SPC/CH liposomes essentially retained the drug over 24 h. A dose of 20 μg/ml amikacin when encapsulated within SPC/PG liposomes was approx. 100-times efficacious against intracellular MAI in the infected alveolar macrophage model in vitro, than an equivalent concentration of free amikacin, indicating that uptake of drug-carrying liposomes by infected macrophages is operative.