Abstract
The relative rates of absorption of a large number of drugs have been measured by perfusing solutions of drugs through the entire small intestine of the anesthetized rat. A single perfusion of the small intestine differentiated very rapid absorption from less rapid absorption. A continuous recirculation of the drug solution through the intestine separated less rapid absorption from very slow absorption.
The degree of ionization of an organic electrolyte in solution appears to be one of the most important factors determining its absorption from the rat small intestine. Acidic drugs were rapidly absorbed if their pKa's were greater than 3. Basic drugs were rapidly absorbed if their pKa's were less than 8. The stronger acids and bases were relatively slowly absorbed and the absorption of very strong acids and bases was imperceptible.
Absorption of drugs from the rat small intestine can be best explained by assuming simple diffusion of unionized drug across a barrier which may be lipoidal in nature.
Footnotes
- Received January 15, 1958.
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