Comparative Evaluation and Optimization of Film Coating Formulation Variables and Delayed Release Properties of Three Enteric Polymers on Diclofenac Sodium Core Tablets

Abstract

Enteric coatings present surfaces that have low permeability in the low pH environments of the stomach and release drug from the underlying core when they reach more neutral to alkaline environments of the intestinal milieu. However, the degree of ester substitution in the polymers, resulting in varied pH/dissolution behaviour, affects the rate and extent of drug release, the suitability of methods to be used and the overall cost of medication. In this study, hydroxypropyl methylcellulose phthalate (HPMCP) and two polymethacrylates, Wangit L30D-55^® and Wangit L-100^® were investigated for their enteric coating properties using diclofenac sodium tablets as core. Both polymers showed acid protective effect at the weight gain of 6%. Polymethacrylate based coatings showed somewhat better surface characteristics and drug release properties than HPMCP. The coating performance of the polymers was found to be better with lower and medium concentration of plasticizer to polymer ratio. The in vitro drug release profiles of the polymethacrylates showed cumulative drug release of 1.72% and 1.69% in 0.1 N HCl over 2 h of release study and 79.5% and 76.1% over 45 min in phosphate buffer pH 6.8, respectively. According to f₂ test, the Wangit L30D-55^® and Wangit L-100^® coated tablets were similar to the two most commonly marketed products of diclofenac sodium 50 mg with f₂ values of 66.66 and 70.88, respectively, for Marketed Product-1 (DilcoDenk^®) and 59.9 and 58.74 for Marketed Product-2 (Remethan^®). The results of the study showed that the polymethacrylates provide better tablet coating properties.

Keywords: enteric coating, hydroxypropyl methylcellulose phthalate, polymethacrylates, diclofenac sodium, optimization