Polyacrylates as Absorption Enhancers

The absorption across rat intestinal tissue of the model peptide drug 9-desglycinamide, 8-L-arginine vasopressin (DGAVP) from bioadhesive formulations was studies by Lehr et al. (1992b) in vitro, in a chronically isolated intestinal loop in situ and after intraduodenal administration in vivo. Only the Polycarbophil suspensions of the drug could show significant increases of bioavailabilities in all three models, whereas a controlled release bioadhesive drug delivery system consisting of microspheres of poly(2-hydroxyethyl methacrylate) with a mucoadhe-sive Polycarbophil coating was practically ineffective, because its mucoadhesive coating was deactivated by soluble mucins before reaching the intestinal mucosa.

A prolongation of the absorption phase in vitro and in the chronically isolated loop in situ suggested that the polymer was able to protect the peptide from proteolytic degradation.

In another study, LueBen and coworkers (1997) compared the absorption enhancing effects of polycarbophil, chitosan, and chitosan glutamate and found that all three mucoadhesive polymers were potent enhancers of the model peptide drug DGAVP using Caco-2 cell layers and the vertically perfused intestinal loop model of the rat. However, the observed comparable transport effect of polycarbophil in the intestinal loop model was mainly ascribed to the protection of DGAVP against proteolytic degradation in the intestinal lumen, which allows for sufficient concentration and thus transport of the peptide drug when a polycarbophil induced paracellular transport is less pronounced.

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