THE USE OF GRAVIMETRY FOR THE STUDY OF THE EFFECT OF ADDITIVES ON THEMOISTURE-INDUCED RECRYSTALLIZATION OF AMORPHOUS LACTOSE

The moisture sorption of amorphous lactose was monitored gravimetrical ly in a humidity controlled microbalance system (CISORP Automated Sorp tion Monitor). The effects of the adding of hygroscopic (polyvinyl pyr rolidone, PVP) and non-hygroscopic excipients (crystalline lactose and colloidal silicon dioxide) on the ability of amorphous lactose to rec rystallise above its glass transition temperature, i.e. at 55 and 75% relative humidity, were studied. PVP was found to delay the time for o nset of weight loss, i.e. the 'apparent' recrystallisation. This is ex plained by PVP acting as an internal desiccant, prolonging the time un til recrystallisation occurs. However, this time was significantly red uced when non-hygroscopic excipients were admired, which is explained by isolation and a deaggregating effect on the amorphous lactose. Thus : gravimetrical studies are well suited for screening the effect of ad ditives on the moisture-induced recrystallisation of amorphous materia ls. (C) 1998 Elsevier Science B.V. All rights reserved.