Adsorption kinetic and mechanistic studies for pharmaceutical spherical carbon adsorbents: Comparison of a brand product and two generics

The kinetic and mechanistic profiles of three pharmaceutical spherical carbon adsorbents, Kremezin as the brand product and two generics (Merckmezin and spherical carbon adsorbent “Mylan”), were compared. Five non-ionic active pharmaceutical ingredients with molecular weights of 136.1–424.1 Da were used as adsorbates. The results of Boehm titration, the standard method to qualify acidic or basic functional groups on a carbon surface, suggested distinctly different quantitative characteristics of each functional group among the three adsorbents. But those differences do not affect the adsorption to non-ionic adsorbates. The amount of theophylline adsorbed at equilibrium and surface area well correlated, suggesting that adsorptive ability was defined by surface area. In the tested molecular weight range, the order in terms of adsorption kinetics was spherical carbon adsorbent “Mylan” > Kremezin > Merkmezin. The adsorption profile in the equilibrium and kinetic experiments, and the lack of an effect of pH on adsorption quantity suggested that the mechanism of adsorption for non-ionic substances to be Langmuir type monolayer adsorption. Kremezin and spherical carbon adsorbent “Mylan” are more likely to adsorb co-administered drugs than Merckmezin.

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► Adsorption kinetics and mechanisms of spherical carbon adsorbents were compared.
► Functional groups on the carbon surfaces were quantitatively different.
► Adsorption kinetic constants were “Mylan” > Kremezin > Merckmezin.
► Adsorption mechanism would be Langmuir type monolayer adsorption for all adsorbents.