An LD50 test being administered

In toxicology, the LD₅₀ or colloquially semilethal dose of a particular substance is a measure of how much constitutes a lethal dose. The test was created by J.W. Trevan in 1927. In animal testing studies, and those of other organisms, the dose administered that kills half the test population is referred to as the LD₅₀, for "Lethal Dose, 50%". Image File history File links LD50mouse. ... Toxicology (from the Greek words toxicon and logos) is the study of the adverse effects of chemicals on living organisms. ... Filmed by PETA, Covance primate-testing lab, Vienna, Virginia, 2004-5. ... A percentage is a way of expressing a proportion or a fraction as a whole number. ...

Animal-rights and animal-welfare groups have campaigned against LD₅₀ testing on animals in particular, citing it as cruel and unnecessary, and in the case of some substances, causing the animals to die slow, painful deaths. Several countries, including the UK, have taken steps to ban the oral LD₅₀, and the Organization for Economic Co-operation and Development (OECD) abolished the requirement for the oral test in 2001 (see Test Guideline 401, Trends in Pharmacological Sciences Vol 22, February 22, 2001). The logo of the Great Ape Project, which is campaigning for a Declaration on Great Apes. ... Animal welfare is the viewpoint that some or all animals, especially those under human care, should be treated in such a way that they do not suffer unnecessarily. ... The Organisation for Economic Co-operation and Development (OECD) is an international organization of those developed countries that accept the principles of representative democracy and a free market economy. ... February 22 is the 53rd day of the year in the Gregorian Calendar. ... 2001: A Space Odyssey. ...

Background

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. The word unit means any of several things: Unit of measurement, a fundamental quantity of measurement Units (computer program), a popular program that does unit conversion Units of energy, the units for energy measurements Units conversion by the Factor-label method Functional unit, a component of a computer system such... The gram or gramme, symbol g, is a unit of mass. ... The international prototype, made of platinum-iridium, which is kept at the BIPM under conditions specified by the 1st CGPM in 1889. ...

The related units of an LD₅₀/30 or an LD₅₀/60 are used to refer to a dose that without treatment will be lethal to 50% of the population within (respectively) 30 or 60 days. These measures are used more commonly within Radiation Health Physics, as survival beyond 60 days usually results in recovery. Health physics is the study of the risks of ionizing radiation to people and the environment. ...

A comparable measurement is LCt₅₀ which relates to lethal dosage from exposure, where C is concentration and t is time. It is often 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 chemical warfare agents. These dosages are typically qualified by rates of breathing (e.g., resting = 10 l/min) for inhalation, or degree of clothing for skin penetration. The concept of Ct was first proposed by Fritz Haber, and is sometimes referred to as Haber's Law, which assumes that exposure to 1 minute of 100 mg/m³ is equivalent to 10 minutes of 10 mg/m³ (1 x 100 = 100, as does 10 x 10 = 100). Some chemicals, such as hydrogen cyanide are rapidly detoxified by the human body, and do not follow Haber's Law. In these cases the lethal dosage is qualified by a duration of exposure (e.g., 10 minutes). In environmental studies, LCt can also refer to the concentration in water instead of air. Chemical warfare is warfare (and associated military operations) using the toxic properties of chemical substances to kill, injure or incapacitate an enemy. ... Fritz Haber in 1918. ... Flash point −17. ...

For disease causing organisms there is also a measure known as the median infective dose and dosage. The median infective dose (ID₅₀) is the number of organisms received by a person or test animal qualified by the route of administration (e.g., 1,200 org/man per oral). Because of the difficulties in counting actual organisms in a dose, infective doses may be expressed in terms of biological assay, such as the number of LD₅₀'s to some test animal. In biological warfare infective dosage is the number of infective doses per minute for a cubic meter (e.g., ICt₅₀ is 100 medium doses - min/m³). Biological warfare, also known as germ warfare, is the use of any organism (bacteria, virus or other disease-causing organism) or toxin found in nature, as a weapon of war. ...

Substances of extreme toxicity (µg/kg)

In the case of neurotoxins, such as batrachotoxin - a poison found in the skins of certain species of Central American and South American frogs and one of the most deadly venoms known - the LD₅₀ is properly and best expressed in terms of micrograms per kilogram (µg/kg) (or billionths) of body mass. The LD₅₀ of batrachotoxin in humans is estimated to be 1 to 2 µg/kg. (This could be more awkwardly expressed as 0.001 to 0.002 mg/kg, but the simpler form of µg/kg is preferred.) It means that merely 0.1 mg of this substance - equivalent to the mass of a couple of grains of ordinary fine table salt - would quickly lead to paralysis, cardiac arrest and death in a 68 kg man. It has been suggested that Neurotoxicity be merged into this article or section. ... Batrachotoxins are extremely potent cardiotoxic and neurotoxic steroidal alkaloids found in certain species of frogs (poison dart frog), Melyridae beetles and birds (Pitohui, Ifrita kowaldi). ... Batrachotoxins are extremely potent cardiotoxic and neurotoxic steroidal alkaloids found in certain species of frogs (poison dart frog), Melyridae beetles and birds (Pitohui, Ifrita kowaldi). ...

See also

• Animal testing
• Vivisection

Filmed by PETA, Covance primate-testing lab, Vienna, Virginia, 2004-5. ... Etymologically, vivisection refers to the dissection of, or any cutting or surgery upon, a living animal including humans. ...

Other measures of toxicity

• Lowest published toxic concentration (TCLo)
• Lowest published lethal dose (LDLo)
• IC₅₀ (50% inhibitory concentration)
• Draize test

Look up toxic and toxicity in Wiktionary, the free dictionary. ... In toxicology the LDLo (Lethal Dose Low) is the lowest dosage per unit of bodyweight (typically stated in mg per kg) of a substance known to have resulted in fatality in a particular animal species. ... The term IC50 represents the concentration of an inhibitor that is required for 50% inhibition of things like an enzyme, a cell receptor or a microorganism. ... The Draize Test is a common animal test devised in 1944 by FDA toxicologist John Draize that involves dropping the tested substance directly into an immobilized animals eyes and observing the results. ...

Related measures

• TCID50 Tissue Culture Infective Dosage
• EID50 Egg Infective Dosage
• ELD50 Egg Lethal Dosage
• Plaque forming units (pfu)