Adsorption of drugs on microcrystalline cellulose suspended in aqueous solutions.

Abstract

The adsorption of various drugs on microcrystalline cellulose (MCC) suspended in aqueous solutions was investigated. Adsorption of diphenhydramine, chlorpheniramine, isoniazid, and p-aminobenzoic acid was very slight or negligible, whereas the adsorption of four phenothiazine derivatives (PTZs) was considerable, and that of acrinol was quite large. Except for chlorpromazine sulfoxide, adsorption isotherms for three PTZs and acrinol were all of the Freundlich type. Based on the Freundlich constants, k and 1/n, the adsorbability of those drugs on MCC was in the order acrinol>>chlorpromazine>triflupromazine>promazine. The slight differences in 1/n for those drugs suggest differences in the adsorption mechanisms. Further it was observed that the adsorption increases with increase of pH, and decreases with increase of ionic strength. In addition, the pH values for MCC suspended solutions decrease gradually with the addition of neutral salts. Thus, in the adsorption of PTZs and acrinol on MCC, the ion-exchange mechanism appeared to play an important role, but adsorption due to non-electrostatic forces should also be appreciable. Marked adsorption of acrinol on MCC can be interpreted in terms of the presence of polar groups capable of hydrogen-bond formation, and the coplanar arrangement of the acridine ring.