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Thread: Quantal Dose-Effect Curves

  1. #1
    PharmD Year 1 TomHsiung's Avatar
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    Jan 2013
    Chengdu, Sichuan, China

    Default Quantal Dose-Effect Curves

    The ED50 in this figure is different from the ED50 in a graded dose-effect curves.

    Graded dose-response curves have certain limitations in their application to clinical decision making. For example, such curves may be impossible to construct if the pharmacologic response is an either-or (quantal) event, such as prevention of convulsions, arrhythmia, or death. Furthermore, the clinical relevance of a quantitative dose-response relation in a single patient, no matter how precisely defined, may be limited in application to other patients, owing to the great potential variability among patients in severity of disease and responsiveness to drugs.

    Therefore, a new type of dose-response curves - Quantal Dose-Effect Curves, is used to overcome these limitations. The curves determines the dose of drug required to produce a specified magnitude of effect in a large number of individual patients or experimental animals and plots the cumulative frequency distribution of responders versus the log dose (the figure above). The specified quantal effect may her chosen on the basis of clinical relevance, or for preservation of safety of experimental subjects, or it may be an inherently quantal event such as death of an experimental animal.

    For most drugs, the doses required to produce a specified quantal effect in individuals are log normally distributed; that is, a frequency distribution of such responses plotted against the log of the dose produces a gaussian normal curve of variation. When these responses are summated, the resulting cumulative frequency distribution constitutes a quantal dose-effeec curve of the proportion or percentage of individuals who exhibit the effect plotted as a function of log dose.

    PS: The term of "drug response" in the discipline of pharmacology can have three different meanings, including 1.Pharmacollogic Action (e.g., the activation of receptors, the block of receptors);2.Physiologic Effect (e.g., the decrease of blood pressure, the increase of heart rate);and 3.Clinical Outcome (e.g., prevention of a heart attack, decrease of the mortality).
    Last edited by TomHsiung; Sat 13th December '14 at 9:57pm.
    B.S. Pharm, West China School of Pharmacy, Class of 2007, Health System Pharmacist, RPh. Hematology, Infectious Disease.

  2. #2


    Quantal dose-effect relationships are measured in a population of subjects that are treated with a range of doses, and the dose is related to the frequency of the all-or-none effect at each dose level. Whereas, Graded dose-effect relationships can be measured in a single biological unit that is exposed to a range of doses, and dose or drug concentration is related to the intensity of the effect.
    Clinical Pharmacy Specialist - Infectious Diseases

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