Optimization of ion-pair formation between glycopyrronium bromide and different ion-pair agents using ACE

Glycopyrronium bromide (GLB) is an anticholinergic drug. Its highly polar quaternary ammonium group could limit the skin permeation of the topical hydrophilic drug. The ion pair formation with suitable anionic molecules was suggested to play a role in enhancing the cationic drug transport to the target site. The interactions between GLB and different ion-pair agents (IPAs) were investigated using ACE. The changes in the effective mobility of 0.05 mM GLB were correlated with the increasing concentrations of IPAs in 20 mM BGE of pH 6.2, and successfully fitted into a nonlinear binding isotherm equation assuming 1:1 stoichiometric interaction. The formation constants (K_f ) were 74.33, 28.5, 18.17, 8.2, 7.6, 5.69, 4.76, and 3.96 M^-1 for sodium salts of dodecyl sulfate, taurodeoxycholate, taurocholate, glycodeoxycholate, glycocholate, salicylate, quinolone sulfonate, and p-toluene sulfonate; respectively. Surfactant's and bile salts' concentrations were below CMCs. The partition coefficient of GLB between buffer phase and n-octanol was determined successfully in the absence and presence of different IPAs. The study confirmed the linear correlation (R² = 0.907) between the affinity strength of ion pair and the partition behavior of GLB in the presence of anionic molecules at 1:1 molar ratio.