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The adsorption of acetohexamide, tolazamide and tolbutamide at pH 7.4 on kaolin and activated charcoal was studied at 37°C. Langmuir adsorption isotherms were established and the maximum adsorption capacities of activated charcoal and kaolin were estimated. The results of desorption experiments suggested that desorption was incomplete, but to a relatively greater extent from activated charcoal than from kaolin. The hypoglycaemic activity of the 3 drugs was suppressed in the presence of both activated charcoal or kaolin.

The release of aminophylline and theophylline embedded in a matrix composed of different ratios of microcrystalline cellulose and glyceryl monostearate (or propylene glycol monostearate) was investigated. The result indicated that drug release within a certain period follows a diffusion-controlled matrix model, where the drug quantity released was proportional to the square root of time. The release rate was found to increase with increasing microcrystalline cellulose—glyceryl monostearate ratio. The logarithm of the rate constant was proportional to the fraction of microcrystalline cellulose in the matrix. The tablets prepared using solvent-evaporated matrix showed quicker release than those prepared from fused ones. Propylene glycol monostearate achieved similar, but somewhat quicker release, than glyceryl monostearate.