CT Index

A measure of drug "potency" calculated from data appropriate to the construction of a Time-Concentration curve; the product of the concentration (C) of an agent applied to a biological system to produce a specific effect and the duration (T) of application required to produce the effect. The index is calculated on the assumption that the time-concentration curve is precisely and symmetrically hyperbolic and convex to the origin, and that the products of the coordinates for all points on the line are constant. The time-concentration curve of an agent with high potentiality for producing a specified effect lies closer to the axis than the curve for an agent of lesser potential; the CT index for the agent of greater potential is smaller than the index for the agent of lesser potential, i.e., the smaller the CT index, the more "potent" the compound. CT indices have found their greatest application in toxicology, in assessing the potential for effect of noxious vapors, etc.
Cf. Time-Concentration Curve, Potency, Dose-Effect Curve, Latent Period