Understanding the interaction between Soluplus (R) and biorelevant media components

Soluplus (R) (polyvinyl caprolactam-polyvinyl acetate-polyethylene glycol graft co-polymer) is a solubilizing copolymer commonly applied as carrier in solid dispersions of poorly soluble drugs. This polymer is used to increase the apparent solubility of drugs with low aqueous solubility and consequently enhance drug absorption by the human gastrointestinal tract. To select the appropriate carrier to compose solid dispersions, in vitro super-saturation studies were applied as a pre-formulation tool, using different dissolution media. During in vitro supersaturation studies performed for the poorly soluble drug candesartan cilexetil, it was found that Soluplus (R) may interact with components of the biorelevant medium Fasted State Simulated Intestinal Fluid, lowering the drug apparent solubility. Dynamic Light Scattering and Transmission Electron Microscopy analyses were performed, as well as fluorescence measurements, aiming to characterize the interaction behavior and determine the polarity of the microenvironment. It was evidenced that Soluplus (R) interacted preferentially with lecithin, forming mixed micelles with a more polar microenvironment, which lowered the candesartan cilexetil solubilization capacity and consequently reduced its apparent solubility in the biorelevant medium. These findings are important to emphasize the key role of the media selection for in vitro solubility-supersaturation studies, where media that could mimic the human gastrointestinal environment are recommended.