Although a toxic response may be observed after exposure to a substance at one particular dose,it is usual to demonstrate responses at several doses of the compound in question and that there is a relationship between the dose and the magnitude of the response.
The shape of the dose-response curve depends on the type of toxic effect measured and the mechanism underlying it.For example,when cyanide reacts with cytochrome a3 it binds irreversibly and curtails the function of the electron transport chain in the mitochondria.As this is a function vital to the life of the cell the dose-response curve for lethality is very steep for cyanide.The more precise the measurement made and the greater the number of determinations the more precise will be the curve and parameters derived from it.