STUDY OF FREE-FILMS AND COATED TABLETS BASED ON HPMC AND MICROCRYSTALLINE CELLULOSE, AIMED FOR IMPROVE STABILITY OF MOISTURE-SENSITIVE DRUGS

Hydrolysis is the dominant process in degradation of drugs, especially for esteric compounds e.g. aspirin. There are several methods for moisture protection of drugs including reduction of drug solubility, modification of chemical structure, moisture-resistant packaging and coating of solid dosage forms. Specific polymer coatings are used to protect moisture sensitive drugs. The aim of this study is to design and evaluate a moisture-resistant film formulation based on HPMC and microcrystalline cellulose (Avicel) and its comparison with Sepifilm® as a commercial gastro- soluble composition for the film coating of moisture sensitive solid dosage forms. Free films of HPMC containing different amounts of Avicel (10, 20, 30 and 40% w/w) and 5% w/w stearic acid as plasticizer were prepared by casting-solvent evaporation method. Free films were then evaluated for their mechanical strength (tensile test), moisture permeability (water vapor transmission test) and morphological properties (SEM). The optimum film formulation was selected to apply as a film coating on tablets containing aspirin (as a moisture sensitive model drug) by fluidized-bed coating. Coated tablets were stored at 40ºC and 75% RH for 2 months. In order to evaluate stability; drug release rate, disintegration time, hardness, and amount of remained aspirin, tablets were studied after 30 and 60 days. The results showed that addition of stearic acid led to improvement of mechanical properties and increase elongation of free films. By increasing amount of Avicel, the water transition rate of free films decreased. HPMC films containing 30% Avicel and 5% stearic acid showed closer properties to Sepifilm® and could be applied as a moisture-resistant film coating and provide acceptable stability for aspirin tablets. These tablets showed the same characteristics as Sepifilm® coated tablets.