LD50 is defined as what?

• A. The dose that produces death in 50% of animals tested
• B. The amount of drug required to cause death in 50% of animals tested
• C. The amount of drug required to produce a specified effect in 50% of animals tested
• D. The maximum effect achieved in all animals at a given dose

Answer: (B)

LD50 is the lethal dose that will kill 50% of a defined test population. It’s a standard single-point measure of acute toxicity used to compare how toxic different substances are, usually expressed as a dose per body weight (for example, mg/kg) and determined by giving different doses to groups of animals and observing mortality within a specified time frame. The option that states the amount of drug required to cause death in 50% of animals tested best captures this idea, since it emphasizes the quantity needed to produce death in half of the population. Remember, LD50 depends on species, route of exposure, and the observation period used.