Potency and Efficacy of a Drug in Intact Organism

When speaking in clinical terms, the efficacy of a drug refers to its ability to produce a desired therapeutic effect, and potency can be expressed as the quantity of drug per kilogram of body weight that can produce a given therapeutic effect. Most of the basic principles of drug action have been discovered and refined using tissue preparations or cell cultures. Such techniques reveal quantitative relationships important in understanding the nature of drug action, but these relationships cannot always be directly translated into clinical efficacy or prediction of side effects. Sometimes the dose-effect curves of drugs in isolated systems and in intact organisms are very similar, but due to pharmacokinetic variables and interactions with multiple target molecules, this is not always the case. The drug may be poorly absorbed from the gastrointestinal tract, or it may be broken down too quickly. It is therefore important to consider the different aspects of pharmacokinetics in evaluating the efficacy and potency of drugs.

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