LD50
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In toxicology, the LD50 or colloquially semilethal dose of a particular substance is a measure of how much constitutes a lethal dose. In toxicological studies of substances, one test is to administer varying doses of the substance to populations of test animals; that dose administered which kills half the test population is referred to as the LD50, for "Lethal Dose, 50%".
This concept was created by J.W. Trevan in 1927.
The usual terms for expressing the LD50 are in units of mass of substance per mass of body mass, eg grams (of substance) per kilogram (of body mass). Stating it this way allows the relative toxicity of different substances to be compared, and allows one to scale for the different size of the animals exposed.
The choice of the 50% mark avoids the potential for ambiguity of making measurements in the extremes.
A comparable measurement is LCt50 which relates to lethal dose by inhalation, where C is concentration and t is time. It is usually expressed in terms of mg-min/m³. ICt50 is the dose which will cause incapacitation rather than death. These measures are commonly used to indicate the comparative efficacy of nerve agents.
The OECD has also recently abolished use of the LD50 known as Test Guideline 401 (Source: TRENDS in Pharmacological Sciences Vol22 No.2 February 2001)
Other measures of toxicity
- Lowest published toxic concentration (TCLo)
- Lowest published lethal dose (LDLo)
- IC50 (50% inhibitory concentration)
- Draize test
Related measures
- TCID50 Tissue Culture Infective Dosage
- EID50 Egg Infective Dosage
- ELD50 Egg Lethal Dosage
- Plaque forming units pfu
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