Formulation and evaluation of sustained release dextromethorphan resinate syrup

ABSTRACT

Aiming to decrease the dosing frequency of the antitussive dextromethorphan, different coated drug resinates were prepared and formulated in syrup form. Polystyrene divinylbenzene sulfonic acid ion exchanger [Amberlite IRP 69, H+ form] was used to prepare the resinates, which were further coated with different concentrations of carnauba wax, Eudragit RL 100, or ethyl cellulose. The in vitro release performance of the coated and uncoated resinates was determined in simulated gastric and intestinal fluids. Selected systems were formulated in syrup form and evaluated for their physicochemical and release performance when fresh and on storage. Dextromethorphan resinates showed relatively rapid release pattern, where 74.2% of the drug released through two hours in acid medium. The release pattern decreased from coated resinates on increasing polymer coat depending on the type of coating polymer. Coated dextromethorphan resinate syrups acquired mixed zero- and first-order release pattern with optimum release rates and suitable first flush values. The dextromethorphan flush in the first five minutes ranged between 9.1 and 12.3% with first-order release rate constants of 0.0048-0.0097 min-1