Moisture sorption, compressibility and caking of lactose polymorphs.Int J Pharm. 2008 Jul 09; 359(1-2):123-34.IJ
The aim of this study was to conduct storage studies on the moisture sorption and caking properties of lactose powder containing different polymorphs (i.e. alpha-monohydrate, alpha-anhydrous unstable, alpha-anhydrous stable, beta-anhydrous) and spray-dried lactose. The dry sample was compacted using a texture analyzer in paper cylinders and stored at relative humidity (RH) of 33%, 43%, 57% and 75% (25 degrees C, for 3 months). The samples were monitored for weight gain, moisture content, alpha/beta balance and hardness. A simple new method of powder compression for measuring the degree of hardness of caked lactose was developed using a texture analyzer. Clear distinctions were found in the storage behavior of the five different samples. Storage at various RHs caused severe caking to beta-lactose anhydrous and spray-dried lactose. The beta-lactose anhydrous was hygroscopic at 75% RH. The spray-dried lactose, which contained some amorphous lactose, was hygroscopic at all RHs studied. Its moisture sorption behavior differed from that of its major component, alpha-lactose monohydrate, by initially absorbing moisture then desorbing. alpha-Lactose monohydrate was less hygroscopic at 75% RH and it formed friable cakes. The alpha-lactose anhydrous stable was hygroscopic at 75% RH and initially formed hard cakes which became friable during storage. The unstable form of anhydrous alpha-lactose was hygroscopic at all levels of RH studied but did not cake.