Quantal Dose—Response: Probits

Abstract

The quantal, or all-or-none, dose—response relation is obtained by specifying a specific endpoint of drug action and determining the number of subjects that achieve this endpoint as a function of drug dosage. For example, the endpoint might be the production of sleep as determined by lack of response to a measured noxious stimulus. A fixed amount of a hypnotic drug is given to a group of animals and the number (or percentage) that experience sleep is noted. A larger dose is given and again the number is determined; this number will include all those who experienced sleep with the previous dose, plus the additional number. Thus, the number, or percentage, is cumulative, resulting in the plotted points shown in Figure 9.1 in which the abscissa is log dose.