Solid-state stability assessment of controlled release tablets containing Carbopol® 971P

A tablet formulation containing dyphylline, Carbomer, magnesium stearate, talc and lactose was prepared by the direct compression method. The objective of the study was to assess the stability of these tablets after subjecting them to exaggerated conditions of temperature (4, 25, 37, 45 and 55 degrees C) and humidity (37 degrees/11%RH, 37 degrees/51%RH and 37 degrees C/91%RH). The samples were analyzed for crystalline, thermal and dissolution changes with time for a period of 12 months using X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and U.S.P. Dissolution Apparatus 2. Moisture sorption studies of all tablets indicated sorption of large amounts of moisture at 37 degrees C/91%RH. The fit factors, f(1) and f(2), were calculated and used to compare the dissolution profiles. The results showed increased f(1) and decreased f(2) values at higher humidity, while the samples were fairly stable at lower humidity and at all temperatures studied. Powder XRD patterns of tablets showed a change in crystallinity at higher humidity. The thermal and crystalline data indicated that the change in dissolution behavior at higher humidity may be due to the conversion of dyphylline to its hydrate form. (C) 1998 Elsevier Science B.V.