The Effects of Plasticizers on the Release of Metoprolol Tartrate from Granules Coated with a Polymethacrylate Film

For coating metoprolol tartrate granules, coating dispersions of Eudragit RS 30 D containing 6%, 12%, or 18% (based on polymer weight) of one of the following plasticizers were used: polyethylene glycol 400 (PEG400), propylene glycol (PG), tributyl citrate (TBC), and triethyl citrate (TEC). The release of metoprolol tartrate from these coated granules was determined at pH 1.2 and 7.4. Slower release resulted from the use of each plasticizer, being slower with increasing concentration of the plasticizer. Release was faster with the more water soluble PEG400 and PG than with TBC and TEC. pH-dependent release was observed with PEG400, PG, and TBC, while TEC gave pH-independent release of drug.