Amphotericin B and monoacyl-phosphatidylcholine form a stable amorphous complex.

Amphotericin B (AmB) is a "life-saving" medicine for the treatment of invasive fungal infections and visceral leishmaniasis. To date, all marketed AmB formulations require parenteral administration, which causes high rates of acute infusion-related side effects and dose-dependent nephrotoxicity. The development of an oral AmB formulation will entail numerous advantages including increased patient compliance, eliminated infusion-related toxicities and reduced nephrotoxicity. Unfortunately, the gastrointestinal absorption of AmB is negligible due to its extremely low solubility in both aqueous and lipid solvents, and its poor gastrointestinal permeability. Drug-phospholipid complexation is an emerging strategy for oral delivery of poorly soluble drugs. In this study, monoacyl-phosphatidylcholine (MAPC) was complexed with AmB forming an AmB-MAPC complex (APC), to enhance the dissolution rate and aqueous solubility of AmB, in order to enable oral delivery of AmB. X-ray powder diffraction demonstrated that AmB was transformed to its amorphous form following complexation with MAPC, i.e. in the APC. Fourier-transform infrared spectroscopy suggested molecular interactions between AmB and MAPC. Dynamic light scattering indicated formation of colloidal structures after aqueous dispersion of APC; Cryogenic transmission electron microscopy showed that APC formed small round, "rod-like" and "worm-like" micellar structures and Small-angle neutron scattering provided three-dimensional micellar structures formed by APC upon aqueous dispersion, which indicated that AmB was inserted into the micellar mono-layer membrane formed by MAPC. Additionally, APC showed an increased dissolution rate and a higher amount of AmB solubilized in fasted state simulated intestinal fluid, compared to AmB/MAPC physical mixtures and crystalline AmB. In conclusion, an APC exhibiting amorphous properties was developed, the APC showed improved dissolution rate and increased apparent aqueous solubility compared to AmB, indicating that the application of APC could be a promising strategy to enable the oral delivery of AmB.