MLD50

MLD50 is a term sometimes encountered in toxicology and related fields, but it is not a standardized or universally accepted metric. In some contexts, MLD50 is described as the minimum lethal dose that would kill 50% of a defined test population, while in others it is used to indicate the smallest dose capable of producing death in 50% of subjects under specified conditions. Because the meaning can vary between studies, many toxicologists reserve the well-established LD50 (lethal dose for 50% of the population) as the conventional measure of acute toxicity.

Interpretation of an MLD50 value depends on several factors, including the species or strain, sex, route of exposure (oral, inhalation, dermal), and the observation period after dosing. Consequently, MLD50 values are not directly comparable across different experiments. The estimation of such a value relies on dose–response data and statistical methods, such as probit or logistic regression, to determine the dose associated with a 50% mortality rate, within the defined experimental context.

Ethical considerations have led to regulatory efforts encouraging alternatives to lethal-dose testing, and some jurisdictions promote non-animal or in vitro approaches. Where MLD50 or LD50 data exist, they should be interpreted with attention to the specific test conditions and species, and not extrapolated indiscriminately to other organisms or real-world exposures.

Related concepts include LD50, TD50 (toxic dose for 50%), NOAEL (no observed adverse effect level), LOAEL (lowest observed adverse effect level), and MTD (maximum tolerated dose). Researchers should clearly define the context when reporting any lethal-dose metric.