Suspensions of prolonged-release diclofenac-Eudragit® and ion-exchange resin microcapsules: II. Improved dissolution stability

Abstract

Purpose: The stability of prolonged release 100 µm -size ion-exchange resin (IER) diclofenac microcapsules (prepared by the Wurster process) and coated with Eudragit® RS30D was evaluated using dissolution analysis.Methods: The IER microcapsules were suspended in 0.1% methylcellulose and stored at 23 and 37°C and the dissolution study conducted over a 6-month period. The surface morphology of the microcapsules was examined using scanning electron microscopy (SEM).Results: The dissolution of the suspensions stored at 23°C on day 1 or 7 and was similar to that of day 30 with slightly faster dissolution on day 60. In contrast, release from suspensions stored at 37°C decreased with storage. The decrease in dissolution with increased temperature was possibly due to the polymer relaxation (micromelting) that was enough to seal the drug within the matrix, resulting in slow dissolution. SEM of the suspended microcapsules correlated with the dissolution data, i.e. the surfaces of microcapsule stored at 37°C showed decreased roughness or smoothening and closing of pores with time and, hence, retardation of drug release, compared with samples stored at 23°C. The dissolution kinetics (shown by the linearity of Bt vs. time profiles) indicated that release mechanism was diffusion.Conclusions: The suspensions of diclofenac IER microcapsules were stable up to 30 days at ambient temperature, which makes the formulation potentially useful as reconstitutable product.