Abstract
We designed a preparation containing both a drug and an adsorbent as a controlled-release system and selected aminophylline as a model drug for use in this study.The preparation consisted of two components: to adsorption equilibrium existing between the drug adsorbed onto an adsorbent and free drug, and diffusion of free drug into blood capillaries via the rectal mucosae. Because of the interlocking of the two components, a continuous supply of the drug via desorption corresponding to the elimination of the drug from the blood circulation was confirmed to be possible, which resulted in maintaining a constant plasma level over a long period following rectal administration.The in vitro release study showed that an optimal adsorbent for the preparation was activated charcoal, especially JP XI grade, and that the most adequate from for rectal administration was by enema. In the in vivo rectal absorption study using rabbits, the preparation provided by an enema enhanced the mean residence time (MRT) of aminophylline by 1.7-fold in comparison with aminophylline solution, and indicated a constant plasma level of theophylline over 6 hours.
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