 in toxicology, the median lethal dose, ld50 (abbreviation for "lethal dose, 50%"), lc50 (lethal concentration, 50%) or lct50 (lethal concentration and time) of a toxin, radiation, or pathogen is the dose required to kill half the members of a tested population after a specified test duration. ld50 figures are frequently used as a general indicator of a substance's acute toxicity. the test was created by j.w. trevan in 1927.what is an ld50 and lc50 the term semilethal dose is occasionally used with the same meaning, in particular in translations from non-english-language texts, but can also refer to a sublethal dose; because of this ambiguity, it is usually avoided. ld50 is usually determined by tests on animals such as laboratory mice. in 2011 the us food and drug administration approved alternative methods to ld50 for testing the cosmetic drug botox without animal tests.   == conventions == the ld50 is usually expressed as the mass of substance administered per unit mass of test subject, typically as milligrams of substance per kilogram of body mass, but stated as nanograms (suitable for botulinum), micrograms, milligrams, or grams (suitable for paracetamol) per kilogram as toxicity decreases. stating it this way allows the relative toxicity of different substances to be compared, and normalizes for the variation in the size of the animals exposed (although toxicity does not always scale simply with body mass). the choice of 50% lethality as a benchmark avoids the potential for ambiguity of making measurements in the extremes and reduces the amount of testing required. however, this also means that ld50 is not the lethal dose for all subjects; some may be killed by much less, while others survive doses far higher than the ld50. measures such as "ld1" and "ld99" (dosage required to kill 1% or 99%, respectively, of the test population) are occasionally used for specific purposes.registry of toxic effects of chemical substances (rtecs)comprehensive guide to the rtecs lethal dosage often varies depending on the method of administration; for instance, many substances are less toxic when administered orally than whe
Toxicology