Changes in Drug Release Rate: Effect of Stress Storage Conditions on Film Coated Mini-Tablets

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Abstract
Film coated theophylline mini-tablets were exposed to stress storage conditions to investigate the effect of changes in temperature and relative humidity (RH) on drug release and the integrity of film coatings. The mini-tablets (3mm in diameter, weighing 20±1 mg) were film coated with polymers such as ethylcellulose with PEG (2:1), ethylcellulose with Eudragit L (2:1) and Eudragit RL. Samples were exposed isothermally at 28,35 and 45°C (constant RH ranging between 55 and 60%) for 21,90 and 180 days, as well as cyclically alternating them every 24h at 45°C, 55% RH; 28°C, 20% RH; and 5°C, 10% RH for 90 days. Dissolution profiles determined after storage were compared with those 24h after initial coating. All samples showed that the coating integrity was maintained. However, dissolution was significantly impeded to a degree directly proportional to temperature, whilst the effect of RH appeared insignificant.