Loss of hydrophobic amine from solution by adsorption onto container surfaces

The apparent loss of the hydrophobic amine drug alpha-[(dibutylamino)methyl]-6,8-dichloro-2-(3',4'-dichlorophenyl)-4-quinoline-methanol monohydrochloride from solution due to its adsorption onto the surface of its storage container was studied. The drug appeared to be adsorbed only as the free base. Therefore, any perturbations to the solution phase that will help solubilize the drug and thus lower its chemical potential will minimize adsorption. Multilayer drug adsorption to the container surfaces appeared to take place, with some evidence of a highly organized system in the adsorbed phase. Adsorption was minimized when the heterogenous polar functionalities on glass surfaces were covered by a layer of silicone or methacrylate polymer, which yielded less reactive, more hydrophobic surfaces. Loss was also minimized when the environment was kept acidic (pH less than or equal to 4,8), the drug was dissolved in a proton-donating solvent (e.g., chloroform), and an ion-pairing agent (e.g., trichloroacetate) was present to solubilize further the monocationic form of the drug in organic media.