Method for screening of solid dispersion formulations of low-solubility compounds—Miniaturization and automation of solvent casting and dissolution testing

An efficient method has been developed for screening solid dispersion formulations that are intended to enhance the dissolution of poorly soluble compounds. The method is based on miniaturization and automation of sample preparation by solvent casting, and dissolution testing, in a 96-well plate format, using less than 0.1 mg of compound per well. To illustrate the method, six polymers and eight surfactants were screened, individually and in combination, for their ability to dissolve a compound with aqueous solubility of <1 μg/ml in simulated intestinal fluid. Screening was performed at an excipient/compound ratio of 10:1, and a polymer/surfactant ratio of 3:1 for ternary formulations. Sixteen of the 48 ternary formulations dissolved the compound to a level >100 μg/ml, i.e. at least a 100-fold increase over the aqueous solubility. A number of synergies were observed wherein the performance of a ternary formulation greatly exceeded that of either of the corresponding binary formulations. Thirteen ‘hits’ from screening were scaled up with melt methods, and ∼2/3 of these showed comparable dissolution enhancement when tested at larger scale. Five of these were administered to rats, and the absolute oral bioavailability ranged from 10 to 23%, versus less than 1% for the unformulated compound.