General Principles Of Pharmacology/Therapeutic index

From Pharmpedia

< General Principles Of Pharmacology

Next Page: Pharmacokinetics
Previous Page: Responses in a population

Fig. 2.6 Dose Response curve and Therapeutic index

The ratio of the drug dose, which produces an undesired effect to the dose, which causes the desired effects, is a therapeutic index and indicates the selectivity of the drug and consequently its usability. It should be noted that a single drug can have many therapeutic indices, one for each of its undesirable effects relative to a desired drug action, and one for each of its desired effects if the drug has more than one action.

Both the positioning and the slope of the cumulative frequency distribution curves for the desired effect, for the side effects, toxic effects and lethal effect are important indicators of the safety of the drug and our ability to use the drug successfully. The important factor is to have a clear gap between the maximum dose required to produce the therapeutic effect and the minimum dose, which will cause death or undesirable side effects. In the case of a shallow slope, the ED50 may not be a useful index.

n refers to the steepness of the slope.

n > 1 is steeper than normal

n < 1 is shallower than normal

Next Page: Pharmacokinetics
Previous Page: Responses in a population