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The sale and use of drugs are regulated in almost all countries by governmental agencies. In the United States, regulation is by the Food and Drug Administration (FDA). New drugs are developed in industrial or academic laboratories. Before a new drug can be approved for regular therapeutic use in humans, a series of animal and experimental human studies must be carried out.

New drugs may emerge from a variety of sources. Some are the result of identification of a new target for a disease. Rational molecular design or screening is then used to find a molecule that selectively alters the function of the target. New drugs may result from the screening of hundreds of compounds against model diseases in animals. In contrast, many (so-called "me-too" drugs) are the result of simple chemical alteration of the pharmacokinetic properties of the original, prototype agent.


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MutagenicAn effect on the inheritable characteristics of a cell or organism—a mutation in the DNA; usually tested in microorganisms with the Ames test
CarcinogenicAn effect of inducing malignant characteristics
TeratogenicAn effect on the in utero development of an organism resulting in abnormal structure or function; not generally heritable
PlaceboAn inactive "dummy" medication made up to resemble the active investigational formulation as much as possible but lacking therapeutic effect
Single-blind studyA clinical trial in which the investigators—but not the subjects—know which subjects are receiving active drug and which are receiving placebos
Double-blind studyA clinical trial in which neither the subjects nor the investigators know which subjects are receiving placebos; the code is held by a third party
INDInvestigational New Drug Exemption; an application for FDA approval to carry out new drug trials in humans; requires animal data
NDANew Drug Application; seeks FDA approval to market a new drug for ordinary clinical use. Requires data from clinical trials as well as preclinical (animal) data
Phases 1, 2, and 3 of clinical trialsThree parts of a clinical trial that are usually carried out before submitting an NDA to the FDA
Positive controlA known standard therapy, to be used along with placebo, to evaluate the superiority or inferiority of a new drug in relation to the others available
Orphan drugsDrugs developed for diseases in which the expected number of patients is small. Some countries bestow certain commercial advantages on companies that develop drugs for uncommon diseases

Because society expects prescription drugs to be safe and effective, governments regulate the development and marketing of new drugs. Current regulations require evidence of relative safety (derived from acute and subacute toxicity testing in animals) and probable therapeutic action (from the pharmacologic profile in animals) before human testing is permitted. Some information about the pharmacokinetics of a compound is also required before clinical evaluation is begun. Chronic toxicity test results are generally not required, but testing must be underway before human ...

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