Lipid based formulations are known to enhance the solubility of drug compounds. The purpose of this study was to determine the intrinsic solubility enhancement of several drug compounds in the presence of a lipid based formulation at 37°C. The ratio of the components in the formulation were varied to investigate the effect of composition on the solubility of the compound.
Using CheqSol, it was possible to readily evaluate the solubility of ionizable compounds at elevated temperatures in the presence of lipid based formulations, which enabled optimization of the composition of the formulation to attain maximum solubility enhancement.
In general, the solubility enhancement improved with the lipophilicity of the compound. However, the extreme enhancement observed for diclofenac may also be influenced by the stabilization of the oily/amorphous form.
The ratio of surfactant:lipid vehicle, at which maximum solubility enhancement was observed, varied between the compounds. For those compounds that have a propensity to form oily droplets (pramoxine, orphenadrine and diclofenac), the ratio was biased towards the lipid vehicle (LabrafacTM). However, it was not clear whether this was influenced by the form of the precipitate or to the lipophilicity of the compound or both.