Effects of hydration on the properties of a roller-dried β-lactose for direct compression

Abstract

The effects of partial and full hydration on the properties of a roller-dried β-lactose for direct compression were evaluated. Gas chromatography, X-ray diffraction and differential scanning calorimetry all indicated that the β-lactose was progressively transformed into β-lactose as hydration increased. Mercury intrusion porosimetry and nitrogen adsorption experiments indicated that the intraparticular porous volume of the β-lactose was considerably increased by full hydration of the excipient; this increase was accompanied by a marked increase in the specific surface of the fully hydrated excipient. The flow properties of the excipient deteriorated progressively as hydration increased, while its compression properties and the mechanical properties of derived tablets were not appreciably affected. Nonetheless, tablets of the fully hydrated excipient had disintegration times very much shorter than those of tablets of the anhydrous and partially hydrated lactose. Finally, incorporation of a small dose of an active principle (4% w/w diazepam) in tablets prepared from the fully hydrated β-lactose had a significant negative effect on their mechanical properties. This effect, together with the above-mentioned increase in the specific surface of the fully hydrated excipient, caused rapid dissolution of the diazepam from these tablets.