The document discusses ex vivo approaches used to study intestinal absorption, including intestinal perfusion, everted gut sac experiments, and Ussing chambers. Intestinal perfusion uses isolated intestinal segments with perfusates to study absorption and metabolism. Everted gut sac experiments use everted intestines filled with a test drug to estimate absorption. Ussing chambers directly measure permeability using intestinal tissue and can study absorption mechanisms. These ex vivo methods provide a means to estimate human intestinal absorption despite some shortfalls.

1. EX vivo Approaches Used to
Study Intestinal Absorption
Prepared by:
Osaid Al Meanazel
Ph.D. student, King Saud University, Saudi Arabia

2. Contents:
• Introduction
• EX vivo Approaches Used to Study Intestinal Absorption
Intestinal perfusion
Everted gut sac experiment
Ussing chamber
• References

3. Introduction
• Bioavailability; commonly defined as the extent and rate at which a drug
becomes available in the general circulation.
• Bioavailability following oral administration is affected by factors such as
dissolution, transit time, enzymatic transformation in digestive juice,
intestinal permeability, biotransformation by intestinal flora tract, and
gastrointestinal and hepatic metabolism.
• intestinal permeability is used for classifying drugs in the Biopharmaceutics
Classification System (BCS).

4. EX vivo Approaches Used to Study
Intestinal Absorption
• Ex vivo methods provide a theoretical means of estimating human
intestine absorption.
• Adequate paracellular permeability is provided by the small intestinal
epithelium, a mucus layer is present in the model, and there is also
expression of transport proteins and drug metabolism.
• Ex vivo sometimes inappropriately estimate the degree of oral absorption.
Despite these shortfalls, ex vivo methods are simple, and widely used in
the design and testing of potential new drugs.

5. Intestinal perfusion: (R. Fisher and Parsons,
1949)
• To study the intestinal absorption and metabolism using isolated perfused
intestinal segments. The surviving intestine preparation is set up apart
from the body and has a viable mucosa.
• Animal intestine are used such as; Pigs, and Bovines. Perfusates are also
used (e.g., Krebs's bicarbonate saline, and Krebs's phosphate saline).
Samples are taken within a predefined time interval.
• The model has a viable mucosa, and it is a quick, simple technique for
estimating of intestinal drug transport.

7. Everted gut sac experiments: Wilson and
Wiseman, 1953)
• After excision, the prepared intestine is everted on a glass and filled with test
drug solution. Absorption is estimated by the differences in weight before and
after draining fluid in the intestine. Samples of luminal medium are taken at the
beginning and end of each run.
• The increase in the initial volume of serosal fluid during the experiment
represents the volume transferred from mucosal to the serosal side of the
preparation.
• The model is simple, and it is very useful for predicting the extent of transfer and
intestinal metabolism of drugs. On the other hand, it tends to gradually lose
structural integrity.

9. Ussing chamber: (Ussing & Zerahn, 1951)
• The Ussing chamber was first described in 1951 for the direct measurement
of unidirectional uptake of sodium from an external solution into frog skin.
• The technique has since been used as an ex vivo model to study the
permeability of intestinal tissue to various molecules.
• it can be used to study the permeability of drugs that are poorly absorbed,
the absorption mechanisms of different compounds, the drug–drug
interactions, and drug transport processes.

11. References
• Luo, Z., Liu, Y., Zhao, B., Tang, M., Dong, H., Zhang, L., Lv, B. and Wei,
L., 2013. Ex vivo and in situ approaches used to study intestinal
absorption. Journal of pharmacological and toxicological
methods, 68(2), pp.208-216.