Objective: The concepts of potency and efficacy are often confused and used interchangeably within the scientific and pharmaceutical industry. It is important that the distinction between the two is understood, and that the terms are defined within their correct context. After reading this article, readers should have an understanding of the relationships between receptor potency and clinical efficacy.
Data sources: Following a comprehensive review of the literature using MEDLINE, the author observed a lack of relevant references that relate measurements of potency to clinical efficacy. Therefore, the author reviewed the basic pharmacologic principles of potency using examples from the recent antihistamine literature.
Results: Potency is an expression of the activity of a drug in terms of the concentration or amount of the drug required to produce a defined effect, whereas clinical efficacy judges the therapeutic effectiveness of the drug in humans. The differing methods of evaluating the activity of antihistamines in vitro and in vivo can lead to inconsistent results, which complicate the use of potency to predict clinical efficacy. Further, as therapeutic behavior is modulated by pharmacokinetic and pharmacodynamic parameters and by further interactions at sites other than the target receptor, it does not necessarily follow that more potent drugs have greater clinical efficacy.
Conclusions: Although potency can be a good preclinical marker of the therapeutic potential of a drug, clinical efficacy should only be evaluated within the patient population using appropriate outcome measures.