| 摘要 |
A novel, closed loop drug delivery system has been developed where the presence or absence of an external compound determines delivery of a drug from a bioerodible polymer. In the described delivery system hydrocortisone is incorporated into a n-hexyl half ester of a methyl vinyl ether-maleic anhydride copolymer and the polymer-drug mixture fabricated into discs. These are then coated with a hydrogel containing immobilized urease. In a medium of constant pH and in the absence of external urea, the release of hydrocortisone is that normally expected for that polymer at the given pH. In the presence of external urea, ammonium bicarbonate and ammonium hydroxide is generated within the hydrogel which accelerates polymer erosion and hence drug release. Drug delivery rate increase is proportional to the amount of external urea and is reversible, that is, when external urea is removed, the rate of drug release gradually returns to its original value.
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