To find out whether a substance that is thought to have medicinal values is safe to use and effective, information on how it affects the body must be gathered. It therefore enters a phase called preclinical testing. Here, scientists from many disciplines must study the chemical and biological properties of the substance. Pharmacology, in its broadest sense, includes the study of how a substance is absorbed, distributed, metabolized or processed, and excreted by the body. These studies are done on small animals in the laboratory.
Substances can be given by mouth (oral), applied to the skin (topical), or be injected or inhaled (parenteral). Absorption studies determine how much of a compound is absorbed after it is given. Some compounds may be destroyed in the stomach by stomach acid so that very little reaches the site where it is needed. How quickly a compound gets to the part of the body where it exerts its effect is called absorption and distribution.
Different substances produce different effects on different parts of the body. Some substances affect only the heart; some, the muscles; and some, the kidneys. This depends on the shape and size of the substance. Correlation between the size and shape of a substance and its effect on the body is called its structure-activity relationship.
Drug metabolism is the study of how a substance is altered or processed in the body so that it can be removed or eliminated (excreted) by the body in the urine or feces.
This information is obtained by giving the substance to a test animal. Samples of blood, urine, and feces are collected at specific times, and the amount of substance present is recorded. All of this information is called the pharmacologic profile of the substance. An autopsy is also done to examine all organs and tissues to give more data. Special studies are also done to see whether the substance is found in the milk of nursing animals. In pregnant animals, studies are done to see if it reaches the developing baby.
Toxicology deals with the unwanted effects of substances. Toxicological studies determine whether a substance can cause nausea, vomiting, changes in eating or drinking habits, weight change or changes in behavior. Work is also done to see if the it can cause cancer (carcinogenic) or produce birth defects (teratogenic).
The manufacture of a substance into a tablet, capsule, or liquid preparation is called formulation. For a substance to be formulated into a suitable dosage form for human use, requires consideration of whether the compound is a solid or liquid, whether it is stable at room temperature, and whether it smells or tastes bad.