Toxicity by Routes
Published Online: 15 DEC 2009
Copyright © 2009 John Wiley & Sons, Ltd. All rights reserved.
General, Applied and Systems Toxicology
How to Cite
Brock, W. J. 2009. Peroral Toxicity. General, Applied and Systems Toxicology. .
- Published Online: 15 DEC 2009
Numerous factors will affect the passage of drugs and chemicals through the gastrointestinal tract and into systemic circulation. These factors involve anatomical and physiological features, species differences and biochemical features, including intestinal metabolism and effects on transporters. With regard to assessing potential risk of humans to chemicals, these features will need to be considered as there will be differences between experimental animals and humans. The cellular environment of the gastrointestinal tract and the molecular mechanisms of absorption will have a major influence on the bioavailability of drugs and chemicals. The pH of the local cell environment will affect the ionization status of the compound, whereas a drug may inhibit cellular transport of other substances, for example, nutrients, potentially having an affect on the nutritional status of the animal. Moreover, there has been demonstrated evidence that some xenobiotics will affect the metabolic status of the gastrointestinal tract. Cytochrome P450 3A is the more common form of cytochrome isoforms found in the intestine, but there are numerous examples that can inhibit, or induce, metabolism much in the same way that hepatic metabolism is affected by chemicals. In addition, the bacterial content of the gastrointestinal tract can affect the absorption of substances primarily by bacterial metabolism. The fasting status of the animal also will affect absorption, and is probably one the more important considerations in the design of a toxicology study. It has been clearly shown that absorption occurs more readily in the fasted animal, and that toxicity may be enhanced since there is a greater surface area of the gastrointestinal tract available for absorption. Finally, chemical interactions will potentially modify absorption through binding of the compound or changing the local cellular environment. From a practical perspective, oral administration of compounds is the most common method for compound administration in toxicology studies. In oral toxicity studies, one will need to consider the drug formulation and the potential effects of the vehicle on the stability as well as the potential toxicity of the vehicle. For the most part, a majority of the vehicles being used currently in laboratories have a long history of use such that toxicity of the vehicle does not become too much of a concern, but the principle of toxicology, the dose makes the poison, should always be a consideration.
- GI transporters;
- factors affecting absorption;
- physiological factors;
- physiochemical factors;
- drug absorption;
- xenobiotic absorption