Influence of dispersion conditions of two pharmaceutical grade clays on their interaction with some tetracyclines

This paper examines the influence of dispersion conditions of two pharmaceutical-grade clay minerals on their interaction with some Tetracyclines. Both the mineralogical and chemical compositions of the clay samples were determined and their structural formulae calculated. Cation exchange capacity (CEC) measurements were also performed on mineral samples, and subsequently, absorption studies were done according to a screening factorial design, by dispersing a known amount of clay in a solution containing a known drug concentration under different conditions (i.e. mixing rate and equilibrium time). The clay samples differed in their mineralogical and chemical compositions, and so must be considered different pharmaceutical materials ("Purified Bentonite" and "Magnesium Aluminum Silicate"). Cation exchange capacities were similar, but different individual amounts of each exchangeable ion as well as amounts of drug retained were detected. Moreover, dispersion conditions greatly affected drug absorption for both minerals. Higher retained amounts were achieved at low equilibrium time when a high mixing rate was applied to broken down clay aggregates. Similar responses were also obtained with low mixing rate as long as a high equilibrium time was used. Therefore, if what is sought is maximum sorption capacity, optimization of dispersion conditions must be achieved before considering any batch test. In particular, high mixing or prolonged equilibrium times increased the amount of drug retained onto the studied clay samples. (c) 2005 Elsevier B.V. All rights reserved.