Plasticisation of amylodextrin by moisture - Consequences for drug releasefrom tablets

Moisture influences the consolidation behaviour of amylodextrin powders and the porosity and mechanical strength of compacts thereof. The aim of this study is to relate moisture content and compact properties to drug release characteristics of amylodextrin tablets. Therefore, amylodextrin tablets co ntaining theophylline monohydrate were prepared and their release character istics were studied as a function of moisture content and initial porosity. Drug release from amylodextrin tablets occurs through a leaching mechanism in which cracks are progressively formed in the hydrated part of the matri x leading to almost constant release rates. Small variations in moisture co ntent resulted in large changes of the release rate. A unique relationship between porosity and release rate, which was independent on moisture conten t and compaction pressure, was observed. Above a critical porosity of 0.075 crack formation was followed by disintegration and fast release. Below thi s critical porosity, tablet:; stayed intact despite of the formation of cra cks, and sustained release was observed. It is concluded that control over moisture content is essential for the production of amylodextrin tablets wi th reproducible release characteristics. Using amylodextrin containing 10-1 7% moisture, tablets with a constant release behaviour can be obtained if s ufficient compaction pressure (> 300 MPa) is applied. Lubrication of amylod extrin powders reduces the effect of porosity significantly and improves th e robustness of amylodextrin tablets as a release controlling excipient in tablets largely. (C) 2000 Elsevier Science B.V. All rights reserved.