Effects of drying process for amorphous waxy maize starch on theophylline release from starch-based tablets

Physical properties and theophylline-release profiles of compressed tablets prepared with amorphous waxy maize starches dried using different methods were examined. A gelatinized waxy maize starch paste (10% solids in water) was either freeze-dried or oven-dried (40 or 105°C) until the moisture content reached to <5%. To form the tablets, the dried amorphous starch powders, either with or without theophylline (3 : 10, w/w), were remoistened to a water content of (17 ± 0.2)%, and compressed into tablets. The drying process applied to the amorphous starch powders affected both the compactness and swelling behavior of the tablets. Although no crystallinity was detected in all the starches tested, X-ray diffraction patterns indicated that starch chains dried at the lower temperature (40°C) are allowed more time to re-associate during the drying process than those dried at the higher temperature (105°C). The freeze-dried starch powders formed tablets characterized by greater compactness and rigidity than was observed in the oven-dried starch samples. The drug release of the tablets prepared with the starch dried at the higher temperature (105°C) occurred at a much slower rate than that of the tablets made with the starch dried at the lower temperature (40°C). The drug release characteristics of the freeze-dried starch tablets were nearly identical to those of the tablets prepared with the Starch dried at 105°C.