Tuesday, February 19 (2019); Pharmacokinetics
In summary, drug absorption in the stomach is usually a minor player in the total absorption of a drug dose. This is because the stomach has a smaller surface area, and the drug usually does not spend very long in there (see the section on gastric motility). Moreover some drugs are ionised by gastric pH and do not absorb very well (i.e. they are less lipid soluble in that state). Some drugs are actually inactivated (degraded) by gastric pH, which reduces their absorption. To be well absorbed in the stomach, a drug would need to be a small molecule, weakly acidic (pKa higher than the pH of stomach acid) and highly concentrated (i.e. a large dose of drug). The typical drug which fulfills all of these criteria is good old ethanol, which traverses the gastric mucosa easily.