Effect of ultraviolet light on the release of theophylline from ethylcellulose-based sustained-release microcapsules

Sustained-release theophylline microcapsules were prepared using the emulsion solvent-evaporation technique. Three viscosity grades of ethylcellulose and varying concentrations of theophylline were used for the formulation. The microcapsules were exposed to short-wave ultraviolet (UV) light for 7 days. The surface and the cross-section of microcapsules were analyzed by scanning electron microscopy (SEM). The release of drug was determined by using the USP dissolution apparatus. Differential scanning calorimetry (DSC) was used to study the thermal properties of theophylline and the polymer. SEM revealed numerous pores on the surface of microcapsules. The size of the pores increased on exposure to light. Theophylline release from microcapsules was found to follow first-order kinetics both before and after UV light exposure. The drug release rate from microcapsules exposed to short-wave UV light increased by about 80%-450% compared with the unexposed samples. The release of theophylline from the microcapsules was more faster with higher concentration of ethylcellulose polymer. Both SEM and DSC showed uniform dispersion of drug with the polymer within the microcapsules. The melting point of the polymers changed, but it remained unchanged for theophylline on exposure to UV light. The UV light caused photodegradation or depolymerization of the polymer and thus caused a faster release of drug from the sustained-release microcapsules. The finding underscores the need for setting standards and requirements for light-stability testing for sustained-release formulations, where there may be substantial change in the release pattern of drug on exposure to light.