Entrapment of drug-loaded ion-exchange particles within polymeric microparticles

The cationic water soluble drugs (chlorpheniramine maleate, pseudoephedrine HCl and propranolol HCl) were bound to a cation-exchange resin (Amberlite(R) IRP 69) and microencapsulated with an aqueous solvent evaporation method, whereby the resin particles were dispersed in an organic polymer solution [ethylcellulose, poly(methyl methacrylate), Eudragit RS 100] followed by emulsification into an external aqueous phase. A key variable for the successful encapsulation was the preferred wettability of the resin particles by the polymer phase. High encapsulation efficiencies were obtained, at high drug loading capacity of the resin, with drugs with high binding affinity and with a wetting agent. Phosphatidyl choline was the preferred wetting agent in order to avoid the partitioning of the resin into the external phase. With Eudragit RS 100, a cationic polymer with quaternary ammonium, all resin particles were encapsulated and the drug release was negligible when compared to the other polymers. This was attributed to the interactions of the polymer with the oppositely charged resin particles, which prevented hydration and swelling of the resin. The drug release depended strongly on the type of polymer used, the microstructure of the microparticles and the binding affinity of the drug to the resin. (C) 1997 Elsevier Science B.V.