Susceptibility to lipase-mediated digestion reduces the oral bioavailability of danazol after administration as a medium-chain lipid-based microemulsion formulation.

Purpose. To investigate the impact of lipidic formulation type on in vitro dispersion and digestion properties and the relationship to oral bioavailability, using danazol as a model lipophilic poorly water-soluble drug. Methods. Three lipid-based danazol formulations [a long-chain triglyceride solution (LCT-solution) and self-microemulsifying drug delivery systems (SMEDDS) based on long-chain (C18) lipids (LC-SMEDDS) and medium-chain (C8-C10) lipids (MC-SMEDDS)] were adminis- tered to fasted beagle dogs and compared with a micronized danazol formulation administered postprandially and in the fasted state. In vitro dispersion and particle size data for the two SMEDDS were compared, and the distribution/solubilization patterns of danazol across the various phases produced during in vitro digestion quantified. Results. The LCT-solution and LC-SMEDDS formulations significantly enhanced the oral bioavailability of danazol when compared to fasted administration of the powder formulation. In contrast, and despite displaying excellent dispersion properties, the MC-SMEDDS resulted in little enhancement in danazol bioavailability. In support of the in vivo findings, in vitro digestion of the medium-chain formulation resulted in significant drug precipitation when compared with the long-chain lipid formulations. Conclusions. Digestion of microemulsion preconcentrate formulations based on medium-chain lipids may limit in vivo utility when compared with similar formulations based on long chain lipids.