General Principles Of Pharmacology/Responses in a population

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The effect of a drug and its variability can be monitored in a population, not necessarily by measuring the response in individuals in the population to a range of different doses, but by measuring the dose required to produce a measured effect. Thus, an end-point to a response or an effect is defined and the dose of drug required to achieve that end-point determined in a group of individuals from the population. A frequency distribution curve would be obtained with the most sensitive members of the population responding and reaching the end-point at the lowest concentrations of the drug, and the most resistant members of the population requiring the highest doses. In this population, the dose required to produce the effect in 50% of the individuals is known as the median effective dose and abbreviated as the ED50. When the frequency distribution curve (red curve) is plotted as a cumulative distribution curve (green curve) a familiar logarithmic dose-response curve is observed.

Fig. 2.5 Cumulative dose response curve

Fig. 2.5 frequency distribution curve (red curve) and cumulative distribution curve (green curve)

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