Assessment of Tunisian clays for their potential application as excipient in pharmaceutical preparations: 2-amino-5-chlorobenzophenone adsorption

The objective of this manuscript was to test the drug-loading and delivery properties of Tunisian clays to demonstrate their potential as low-cost excipients in pharmaceutical formulations. Raw kaolinite, purified smectite, and organophilic smectite were studied for the adsorption and desorption of 2-amino-5-chlorobenzophenone (2A-5BC) as a drug model molecule. The adsorption and desorption properties of these clay samples were investigated under different pH conditions, including those emulating the intestinal and gastric fluids from human body. DFT calculations were performed to characterize the atomic interactions involved in the adsorption mechanism. The adsorption and desorption properties of these clays were correlated with their main physicochemical properties and textural parameters. The maximum 2A-5BC adsorption (i.e., 48.2 mg/g) was achieved using smectite functionalized with HDTMA. Electrostatic forces and hydrogen bonds played a relevant role during 2A-5BC adsorption. The desorption of 2A-5BC from clay samples was effective at 37 °C and pH similar to the intestinal and gastric fluids, thus reaching desorption efficiencies of up to 93%. 2A-5BC desorption data were modeled with the Korsmeyer-Peppas equation and the results indicated the presence of a non-Fickian mass transport. Tunisian smectite functionalized with HDTMA presented promising performance and can be considered as a potential excipient in pharmaceutical formulations.