PHARMACOKINETICS

 

INTRODUCTION: The term pharmacokinetics is derived from the root words pharmaco, which means “medicine,” and kinetics, which means “movement or motion.” Pharmacokinetics is thus the study of drug movement throughout the body. In practical terms, it describes how the body deals with medications. Pharmacokinetics is a core subject in pharmacology, and a firm grasp of this topic allows the medical professionals to better understand and predict the actions and side effects of medications in patients. Drugs face numerous obstacles in reaching their target cells.  When we are addressing pharmacokinetic aspects of a drug, we shall be looking at its absorption from the site of injection or administration, distribution in the body tissues, metabolism and then it excretion from the body.

ABSORPTION OF DRUGS:  For most medications, the greatest barrier is crossing the many membranes that separate the drug from its target cells. A drug taken by mouth, for example, must cross the plasma membranes of the mucosal cells of the gastrointestinal tract and the capillary endothelial cells to enter the bloodstream. The plasma membrane

To leave the bloodstream, the drug must again cross capillary cells, travel through the interstitial fluid, and depending on the mechanism of action, the drug may also need to enter target cells and cellular organelles such as the nucleus, which are surrounded by additional membranes.  These are examples of just some of the barriers that a drug must successfully penetrate before it can produce a response. 

METABOLISM OF DRUGS:  While moving toward target cells and passing through the various membranes, drugs are subjected to numerous physiological processes. For medications given by the enteral route, stomach acid and digestive enzymes often act to break down the drug molecules. Enzymes in the liver and other organs may chemically change the drug molecule to make it less active.  If the drug is seen as foreign by the body, phagocytes may attempt to remove it, or an immune response may be triggered. 

DRUG EXCRETION:  The kidneys, large intestine, and other organs attempt to excrete the medication from the body. These examples illustrate pharmacokinetic processes: how the body handles medications. The many processes of pharmacokinetics are grouped into four categories: absorption, distribution, metabolism, and excretion as we have briefly seen here, and we shall be seeing in our next discussions in details.

RELATED;

1.  ROUTES OF DRUG ADMINISTRATION  

2.  BIOAVAILABILITY

3.  DYNAMICS OF DRUGS AND THE HUMAN BODY

4.  DRUG METABOLISM

5.  THE PLASMA MEMBRANE

6.  PHARMACOLOGY AND THERAPEUTICS

REFERENCES