Many of the drugs in current use were discovered by experiments conducted in animals and humans. However, many drugs are now being designed with the specific disorder in view. Abnormal biochemical and cellular changes caused by disease are identified, and then compounds that may specifically prevent or correct these abnormalities (by interacting with specific sites in the body) can be designed. When a new compound shows promise, its structure is usually modified many times to optimize its ability to target the intended site (selectivity), remain attached to the site (affinity), and optimize its strength (potency), effectiveness (efficacy), and safety (side effects). Other factors, such as whether the compound is absorbed through the intestinal wall and whether it is stable in body tissues and fluids, are also considered. These factors involve what the body does to the drug (drug kinetics—see Administration and Kinetics of Drugs: Introduction to Administration and Kinetics of Drugs) and what the drug does to the body (drug dynamics—see Drug Dynamics: Definition of Drug Dynamics).
Ideally, a drug is highly selective for its target site, so that it has little or no effect on other body systems—that is, it has minimal or no side effects (see Adverse Drug Reactions: Overview of Adverse Drug Reactions). The drug should also be very potent and effective, so that low doses can be used, even for disorders that are difficult to treat. The drug should be effective when taken by mouth (for convenient use), absorbed well from the digestive tract, and reasonably stable in body tissues and fluids so that, ideally, one dose a day is adequate.
During drug development, standard or average doses are determined. However, people respond to drugs differently. Many factors, including age (see Aging and Drugs), weight, genetic make-up, and the presence of other disorders, affect drug response (see Factors Affecting Response to Drugs: Overview of Response to Drugs). These factors must be considered when doctors determine the dose for a particular person.
Last full review/revision May 2007 by Eva M. Vivian, PharmD