Pharmacokinetics What Can Happen To A Drug In The Body Drug Absorption

Any drug must reach its target molecules before it can exert any effect. The first obstacle lies in the tissues that the drug molecules must penetrate in order to reach blood, which can carry them to the target. Drug absorption is this process whereby a drug reaches the bloodstream from the locus where it is applied to the body. Not all of the drug reaches the blood. Bioavailability, the term that reflects the extent to which a drug is absorbed, refers to the proportion of drug administered that actually reaches blood. (It may seem more desirable to know the concentration of the drug at the site of action, but such measurements would in most cases be impractical or even impossible.) Bioavailability depends upon the drug, the drug formula, the route of administration, and the physiological conditions in the organism. For example, drugs with high solubility in lipids are more easily absorbed, and the lipid solubility of many drugs is influenced by the pH levels in the immediate aquous media because acidity influences ionization of the drug molecules, and drugs in an ionized state are less soluble in lipids. On the other hand, the influence of physicochemical factors on drug absorption depends upon which tissue the drug is applied: Lipid solubility is critical for drugs administered orally or on the skin, but in the vicinity of the peripheral capillary beds (like after administration into the muscle), a drug is absorbed well regardless of its ionization level. An example of the intentional manipulation of absorption rates is the modern pharmaceutical industry's ability to tailor drug formulas to release the active ingredient either faster or more slowly, as in depot preparations of antipsychotics, where the slow hydrolysis of ester bonds supports prolonged release of the drug over a period of weeks at a constant rate.

0 0

Post a comment