Quantal dose-response relationship

E. Quantal Dose-Response Relationships When the minimum dose required to produce a specified response is determined in each member of a population, the quantal dose-response relationship is defined (Figure 2-2). When plotted as the fraction of the population that responds at each dose versus the log of the dose administered, a cumulative quantal dose-response curve, usually sigmoid in shape, is obtained. The median effective (ED j,), median toxic (TD, ), and median lethal doses (LD j,) are extracted from experiments carried out in this manner. 

In addition to the responsiveness of a given patient, one may be interested in the relationship between dose and some specified quantum of response among all individuals taking that drug. Such information is obtained by evaluating data obtained from a quantal dose-response curve. 

Quantal dose-response curves based on all-or-none responses. A. Relationship between the dose of phenobarbital and the protection of groups of rats against convulsions. B. Relationship between the dose of phenobarbital and the drug s lethal effects in groups of rats. ED50, effective dose, 50% LD50, lethal dose, 50%. 

It is clear from the earlier discussion that the measurable endpoint of toxicity may be a pharmacological, biochemical, or a pathological change, which shows percentage or proportional change. Alternatively, the endpoint of toxicity may be an all-or-none or quantal type of effect such as death or loss of consciousness. In either case, however, there will be a dose-response relationship. The basic form of this relationship is shown in Figure 2.4. 

Dose Rate The chemical s dose delivered per unit lime or the radiation dose delivered per unit time. Dose-Response Curves Demtnstrate the relation between dose and the proportion of individuals responding with a quantal effect (q.v.). In general, dose-response curves are S-shaped (increasing), and they have upper and lower asymptotes, usually but not always 1(X) and 0%. D Response Relationship The systematic relationship between the dose (or effective concentration) of a drug or xenobiotic and the magnitude (or intensity) of the response it elicits. 

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