Gastrointestinal residence time, effect

P = effective permeability, r = intestinal radius, and = residence time in the small intestine [2]. The critical assumptions in this relationship are (1) that the drug is in solution and hence available for transport across the intestinal membrane and (2) the drug is chemically stable in the gastrointestinal tract and not a substrate for proteolytic or metabolic enzymes in the intestinal lumen or gut mucosa. These are highly simplifying assumptions. The inappropriate use of Eq. (2) to calculate absorption for compounds that are limited by solubility, instability, or metabolism can lead to seriously erroneous and misleading conclusions. [Pg.247]

When tested in many species of animals and birds, tetramisole was effective against a wide range of gastrointestinal nematodes and exhibits only mild side effects in most cases. Host of the biological activity of the mixture of tetramisole resides in the levorotatory isomer, levamisole, which is several times more potent but no more toxic than the dextrorotatory isomer, dext rami sole. ... [Pg.224]

Big Chemical Encyclopedia