Drug Dosages Health Article

Definition

Drug dosage refers to the determination and regulation of the amount, frequency, and number of times a specific quantity of medication is to be administered. For legal purposes in the United States, a drug is considered to be any substance (other than a food or a device) intended for use in diagnosis, cure, relief, treatment, or prevention of disease, or to affect the structure or function of the body. However, a simple, working definition of a drug is any chemical that affects the processes of the mind or body, and the dose is the amount to be administered at one time.

Purpose

The selection of a drug for use in an individual requires two primary considerations: pharmacodynamics (what the drug does to the body) and pharmacokinetics (what the body does to the drug over time). Pharmacodynamics not only involves considering what the drug does as in lowering blood pressure, relieving pain, or fighting an infection, but where (the site) and how (mechanism of action) the drug acts on the body. Often, what the drug does is immediately obvious, but the exact site and mechanism of action may not be understood until after many years of use.

For a drug to work, it has to get to the place in the body where it is needed, and this requires the science of pharmacokinetics. Sufficient amounts of a drug must stay at the site of its required action until the job is completed, but not so much that severe side effects or toxic reactions

KEY TERMS

Conjugations—The joining of a chemical substance with another to form a new product.

Hydrolysis—The breaking up of a chemical compound by the addition of water.

Lipids—A group of substances composed of fatty, greasy, oily, and waxy compounds that are insoluble in water and soluble in nonpolar solvents or most organic solvents.

Metabolism—The sum of the physical and chemical processes by which living organized substance is built up and maintained and by which large molecules are broken down into smaller molecules to make energy available to the organism.

Oxidation—The chemical reaction whereby electrons are removed from the atoms of a substance for transferal.

Perfused—The act of the passage of a fluid through the vessels of a specific organ or tissue.

Phospholipids—Any lipid or fatty substance that contains phosphorus; the major lipids in cell membranes.

Reduction—The gaining of electrons during a chemical reaction.

Semi-permeable—Permitting passage only of certain molecules.

Therapeutic window—A drug's ability to maintain a specific level of action over a specific period of time.

are produced. Many drugs get to their site of action through the bloodstream. Therefore, how much time they need to work and how long their effects will last can depend on how fast they get into the bloodstream, how much gets into the bloodstream, how fast they leave the bloodstream, how easily and efficiently they are broken down (metabolized) by the liver, and how soon they are eliminated by the kidneys and intestines.

Drugs affect only the speed of biologic functions and do not change the basic character of existing processes nor generate new functions. This means that drugs can either speed up or slow down biochemical reactions in the body, as in how fast or slow a nerve may transmit a message, or how fast or slow a muscle may contract. Although drugs can change the rate of a biological process, they cannot re-establish a system that is injured beyond repair.

Every person responds to a drug differently. Thus, it is difficult to determine what dosage of a drug should be administered to each individual. Since drugs undergo testing in animals and trials in humans, an average dose is determined from these studies. An appropriate response to a drug requires the appropriate concentration of the drug at the site of action. The appropriate concentration and dosage regimen depend on individuals' clinical state, the severity of their disorder, the presence of a diseased state, the use of other drugs, as well as other considerations. Drug administration must be determined by each individual's needs, which requires an accurate evaluation of drug dosage.