The effect of powder blend and tablet structure on drug release mechanisms of hydrophobic starch acetate matrix tablets

This study investigates the release mechanism of a hydrophilic drug (caffeine) from hydrophobic matrix tablets composed of starch acetate. Different particle size fractions of starch acetate were mixed with caffeine (22% V/V) to obtain various mixture organisations in the powder, as 14 well as in the final tablet. The organisation of powder mixtures was calculated by the carrier payload of starch acetate particles, while the pore size distributions in tablets were measured by mercury intrusion porosimetry. A carrier payload below I indicated the existence of a free starch acetate particle surface, while numbers greater than 1 pointed to a complete occupation of the starch acetate particle surface area by caffeine particles. The carrier payload calculations gave a good prediction for the existence of a starch acetate matrix in the tablet structures. Caffeine matrices in tablets compressed from the mixtures could be detected by mercury intrusion porosimetry measurements. The existence of different matrices, as well as different pore networks, determined the physical changes of the tablets and the release mechanism of caffeine during dissolution tests. When a tablet contained only a caffeine matrix, rapid tablet disintegration and immediate release of the total amount of caffeine occurred. A single matrix of starch acetate resulted in tablets that remained intact, although cracks were formed. The co-existence of matrices of both materials created surface erosion of the tablet. The caffeine release profiles of tablets that remained intact or showed erosion were fitted by an equation containing both diffusional and relaxational factors to describe the effect of tablet porosity on drug release. (c) 2005 Elsevier B.V. All rights reserved

Ultrasound Transmission Technique as a Potential Tool for Physical Evaluation of Monolithic Matrix Tablets

The aim of this study was to investigate the effects of tablet porosity and particle size fraction of compacted Starch acetate powders, with and without model drug caffeine, on acoustic properties of tablets. The ultrasound velocity was determined from the transmission measurements. Tablets of starch acetate (SA DS 2.7) powder with two particle size fractions of 0–53 and 0–710 μm were compressed with a compaction simulator. Porosities of tablets varied in the range from 12% to 43% for both particle size fractions. Strong associations were found between the ultrasound velocity and physical properties of the tablets such as porosity and particle size fraction. Interestingly, ultrasound velocity was practically insensitive to inclusion of the model drug caffeine with the concentrations used. Based on this study ultrasound transmission method is a potential non-destructive tool for studying structural changes of tablets and other solid dosage forms