Effective dose (pharmacology)

In pharmacology, an effective dose (ED) or effective concentration (EC) is the dose or concentration of a drug that produces a biological response.^[1][2] The term "effective dose" is used when measurements are taken in vivo, while "effective concentration" is used when the measurements are taken in vitro.^[3]

It has been stated that any substance can be toxic at a high enough dose. This concept was exemplified in 2007 when a California woman died of water intoxication in a contest sanctioned by a radio station.^[4] The line between efficacy and toxicity is dependent upon the particular patient, although the dose administered by a physician should fall into the predetermined therapeutic window of the drug.

The importance of determining the therapeutic range of a drug cannot be overstated. This is generally defined by the range between the minimum effective dose (MED) and the maximum tolerated dose (MTD). The MED is defined as the lowest dose level of a pharmaceutical product that provides a clinically significant response in average efficacy, which is also statistically significantly superior to the response provided by the placebo.^[5] Similarly, the MTD is the highest possible but still tolerable dose level with respect to a pre-specified clinical limiting toxicity.^[5] In general, these limits refer to the average patient population. For instances in which there is a large difference between the MED and MTD, it is stated that the drug has a large therapeutic window. Conversely, if the range is relatively small, or if the MTD is less than the MED, then the pharmaceutical product will have little to no practical value.^[5]