Essay Pharmacology
Luca Chiara Jacobs Group 6!
Drug Absorption
The study of drug absorption, distribution, metabolism, excretion, and how the body
affects the drug falls under the term pharmacokinetics. The application of
pharmacokinetic methods to ensure patients are treated safely and effectively is
known as clinical pharmacokinetics. The introduction of pharmacokinetics as a
discipline has facilitated the development of rational drug therapy, understanding
drug action and metabolism, understanding of concentration-effect relationship, and
the establishment of dosage regimens.
The most important principle in pharmacokinetics theory is drug absorption which is
defined as the transportation of the unmetabolized drug from the site of
administration to the body circulation system. Several mechanisms of drug absorption
have been identified, including passive diffusion, carrier-mediated membrane
transport such as active and facilitated diffusion, and other nonspecific drug
transporters, such as P-glycoprotein. Different factors can affect drug absorption;
these factors can be classified as drug-specific and patient-specific factors. Therefore,
the percentage of drug absorption is varied among different routes of administration,
such as oral, subcutaneous (SQ), transdermal, intravenous (IV), and intramuscular
(IM). Since the oral route is the major route of administration, the major emphasis of
this article will be on gastrointestinal (GI) drug absorption. The bioavailability of a
drug product is known as the rate and extent of its absorption. A better understanding
of the drug absorption process and affecting factors play an important role in
achieving better bioavailability and thus better therapeutic effect.
For drug absorption to occur, a drug must cross biologic barriers
(e.g. epithelial/endothelial cells ). Only a few drugs move across cellular barriers in
an “active” way; that is, a way that requires energy (ATP) and moves the drug from
an area of low concentration to an area of higher concentration.
On the other hand, most drugs cross cellular barriers via passive diffusion; that is,
drugs simply move from an area of higher concentration to an area of lower
concentration by diffusing through cell membranes.
