Which of the following terms describes the lethal-dose metric used in preclinical testing?

• A. TD50
• B. LD50
• C. ED50
• D. TD60

Answer: (B)

Lethality as the endpoint is quantified by the dose that causes death in a population. The dose that results in death for 50% of subjects is the LD50, a classic measure of acute lethality used in preclinical safety testing. It is determined by exposing groups to escalating doses and recording mortality, then fitting a dose–response curve to find the dose at which half the subjects die. This differs from ED50, which is the dose for 50% of subjects to achieve the desired therapeutic effect, and TD50, which is the dose for 50% to experience a toxic (often non-lethal) adverse effect. There is a TD60 concept as well, but it’s not the standard lethality metric. So the term describing the lethal-dose metric in preclinical testing is LD50.