The Effect of Humidity on Hydration Kinetics of Mixtures of Nitrofurantoin Anhydride and Diluents

Abstract

The effect of humidity on mixtures of nitrofurantoin and crystalline lactose or microcrystalline cellulose was investigated by X-ray diffraction analysis, water content measurement and thermogravimetry. The water content of 50% (w/w) mixture was measured after storage at 95 and 100% relative humidity (RH), 40°C for 24h. The hydration of the mixture containing microcrystalline cellulose at 95% RH was the slowest, and that containing lactose at 100% RH was the fastest. The hydration process of nitrofurantoin anhydride was analyzed based on the three-dimensional phase boundary theory. The hydration rate of the nitrofurantoin was accelerated by adding lactose, but not by microcrystalline cellulose. Since lactose had a critical relative humidity at around 95% RH, the hydration of the mixture occurred in the solution after the lactose rapidly dissolved by deliquescence. However, the hydration rates of the mixture with microcrystalline cellulose were much slower than those of the anhydride.