Comparison of a spray-dried alpha-lactose monohydrate with a fully hydrated roller-dried beta-lactose

We compared the properties of two lactoses chiefly composed of alpha-lactose monohydrate: one was a spray-dried alpha-lactose (DCL-11), the other a roller-dried beta-lactose that had been fully hydrated and then sieved and reconstituted (DCL-21(H)) so that its particle size was similar to that of the first. As regards their structural properties, the lactoses were similar; however, their particles differed in that those of DCL-21(H) had greater specific surface and intraparticular porosity, and those of DCL-11 had higher sphericity, which afforded this lactose flow properties very much superior to those of DCL-21(H). As regards the compressed lactoses, the above-mentioned differences in the porosity and specific surface, together with their lower mechanical resistance, caused DCL-21(H) tablets to disintegrate very much faster than DCL-11 tablets. Incorporation of a small dose (4% w/w) of diazepam in tablets of DCL-11 caused both their tensile strengths and disintegration times to decrease to values close to those of DCL-21(H) tablets, which were not significantly altered by incorporation of diazepam. Finally, due to the greater specific surface of the DCL-21(H) tablets, the rate of dissolution of diazepam from them was significantly faster than from the DCL-11 tablets.