ED50

ED50, short for median effective dose, is the dose of a drug or other agent that produces the defined desired effect in 50 percent of a population or experimental subjects. It is a standard measure of potency used to compare doses required to achieve a given response across drugs or formulations. In pharmacology and toxicology, ED50 is derived from dose–response data and is typically estimated from a sigmoid curve using probit, logistic, or Hill equation models. In quantal endpoints, the ED50 is the dose at which half of the subjects exhibit the endpoint; in graded responses, ED50 is the dose that yields 50 percent of the maximum effect.

The value is influenced by many factors, including species or strain, sex, age, route of administration, formulation, and the specific endpoint being measured (for example analgesia, sedation, or antiemesis). Different ED50s may be reported for the same drug if a different endpoint or population is specified. ED50 is related to other concepts of potency and safety such as ED90, EC50 (the concentration for 50 percent of maximal effect in vitro), and LD50 (the lethal dose for 50 percent of subjects). It is not a fixed property of a compound; it depends on experimental conditions and the chosen endpoint.

Limitations: ED50 does not convey the therapeutic window or safety margin. It represents population-average potency and carries uncertainty that is usually expressed with confidence intervals.