Median lethal dose

In toxicology, the median lethal dose, LD₅₀ (abbreviation for "lethal dose, 50%"), LC₅₀ (lethal concentration, 50%) or LCt₅₀ is a measure of the lethal dose of a toxin, radiation, or pathogen. The value of LD₅₀ for a substance 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. A lower LD₅₀ is indicative of increased toxicity.

The test was created by J.W. Trevan in 1927.^[1] 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.^[2][3]

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, sometimes also stated as nanograms (suitable for botulinum), micrograms, or grams (suitable for paracetamol) per kilogram. 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.^[4]

Lethal dosage often varies depending on the method of administration; for instance, many substances are less toxic when administered orally than when intravenously administered. For this reason, LD₅₀ figures are often qualified with the mode of administration, e.g., "LD₅₀ i.v."

The related quantities LD₅₀/30 or 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.

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. LCt₅₀ is the dose that will cause incapacitation rather than death. These measures are commonly used to indicate the comparative efficacy of chemical warfare agents, and 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 × 100 = 100, as does 10 × 10 = 100).

Some chemicals, such as hydrogen cyanide, are rapidly detoxified by the human body, and do not follow Haber's Law. So, in these cases, the lethal concentration may be given simply as LC₅₀ and qualified by a duration of exposure (e.g., 10 minutes). The Material Safety Data Sheets for toxic substances frequently use this form of the term even if the substance does follow Haber's Law.

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).

Limitation

As a measure of toxicity, LD₅₀ is somewhat unreliable and results may vary greatly between testing facilities due to factors such as the genetic characteristics of the sample population, animal species tested, environmental factors and mode of administration.^[5]

There can be wide variability between species as well; what is relatively safe for rats may very well be extremely toxic for humans (cf. paracetamol toxicity), and vice versa. For example, chocolate, comparatively harmless to humans, is known to be toxic to many animals. When used to test venom from venomous creatures, such as snakes, LD₅₀ results may be misleading due to the physiological differences between mice, rats, and humans. Many venomous snakes are specialized predators on mice, and their venom may be adapted specifically to incapacitate mice; and mongooses may be exceptionally resistant. While most mammals have a very similar physiology, LD₅₀ results may or may not have equal bearing upon every mammal species, such as humans, etc.

Examples

NOTE: Comparing substances (especially drugs) to each other by LD₅₀ can be misleading in many cases due (in part) to differences in effective dose (ED₅₀). Therefore, it is more useful to compare such substances by therapeutic index, which is simply the ratio of LD₅₀ to ED₅₀.

The following examples are listed in reference to LD₅₀ values, in descending order, and accompanied by LC₅₀ values, {bracketed}, when appropriate.

Substance	Animal, Route	LD50 {LC50}	LD50 : g/kg {LC50 : g/L} standardized	Reference
Water	rat, oral	>90g/kg	>90	[6]
Sucrose (table sugar)	rat, oral	29,700 mg/kg	29.7	[7]
Monosodium glutamate (MSG)	rat, oral	16,600 mg/kg	16.6	[8]
Vitamin C (ascorbic acid)	rat, oral	11,900 mg/kg	11.9	[9]
Urea	rat, oral	8,471 mg/kg	11.5	[10]
Cyanuric acid	rat, oral	7,700 mg/kg	7.7	[11]
cadmium sulfide	rat, oral	7,080 mg/kg	7.08	[12]
Grain alcohol (ethanol)	rat, oral	7,060 mg/kg	7.06	[13]
sodium isopropyl methylphosphonic acid (IMPA, metabolite of sarin)	rat, oral	6,860 mg/kg	6.86	[14]
Melamine	rat, oral	6,000 mg/kg	6	[11]
Melamine cyanurate	rat, oral	4,100 mg/kg	4.1	[11]
Sodium molybdate	rat, oral	4,000 mg/kg	4	[15]
Table Salt	rat, oral	3,000 mg/kg	3	[16]
Paracetamol (acetaminophen)	rat, oral	1,944 mg/kg	1.944	[17]
Delta-9-tetrahydrocannabinol (THC)	rat, oral	1,270 mg/kg	1.27	[18]
Metallic Arsenic	rat, oral	763 mg/kg	0.763	[19]
Alkyl dimethyl benzalkonium chloride (ADBAC)	rat, oral fish, immersion aq. invertebrates, imm.	304.5 mg/kg {0.28 mg/L} {0.059 mg/L}	0.3045 {0.00028} {0.000059}	[20]
Coumarin (benzopyrone, from Cinnamomum aromaticum and other plants)	rat, oral	293 mg/kg	0.293	[21]
Aspirin (acetylsalicylic acid)	rat, oral	200 mg/kg	0.2	[22]
Caffeine	rat, oral	192 mg/kg	0.192	[23]
Arsenic trisulfide	rat, oral	185–6,400 mg/kg	0.185-6.4	[24]
Sodium nitrite	rat, oral	180 mg/kg	0.18	[25]
uranyl acetate dihydrate	mouse, oral	136 mg/kg	0.136	[26]
Bisoprolol	mouse, oral	100 mg/kg	0.1	[27]
Cobalt(II) chloride	rat, oral	80 mg/kg	0.08	[28]
Cadmium oxide	rat, oral	72 mg/kg	0.072	[29]
Sodium fluoride	rat, oral	52 mg/kg	0.052	[30]
Pentaborane	human, oral	<50 mg/kg	<0.05	[31]
Capsaicin	mouse, oral	47.2 mg/kg	0.0472	[32]
Mercury(II) chloride	rat, dermal	41 mg/kg	0.041	[33]
Lysergic acid diethylamide (LSD)	rat, intravenous	16.5 mg/kg	0.0165	[34]
Arsenic trioxide	rat, oral	14 mg/kg	0.014	[35]
Metallic Arsenic	rat, intraperitoneal	13 mg/kg	0.013	[36]
Nicotine	human, oral	6.5-13.0 mg/kg (estimated)	0.0065-0.013	[37]
Sodium cyanide	rat, oral	6.4 mg/kg	0.0064	[38]
White phosphorus	rat, oral	3.03 mg/kg	0.00303	[39]
Strychnine	human, oral	1–2 mg/kg (estimated)	0.001	[40]
Cantharidin	human, oral	0.5 mg/kg	0.0005
Aflatoxin B1 (from Aspergillus flavus)	rat, oral	0.48 mg/kg	0.00048	[41]
Venom of the Brazilian wandering spider	rat, subcutaneous	134 µg/kg	0.000134	[42]
Venom of the Inland Taipan (Australian snake)	rat, subcutaneous	25 µg/kg	0.000025	[43]
Ricin	rat, intraperitoneal rat, oral	22 μg/kg 20–30 mg/kg	0.000022 0.02	[44]
2,3,7,8-Tetrachlorodibenzodioxin (TCDD, a dioxin)	rat, oral	20 µg/kg	0.00002	[45]
Sarin	mouse, subcutaneous injection	17.23 µg/kg (estimated)	0.0000172	[46]
VX	human, oral, inhalation, absorption through skin/eyes	2.3 µg/kg (estimated)	0.0000023	[47]
Batrachotoxin (from poison dart frog)	human, sub-cutaneous injection	2-7 µg/kg (estimated)	0.000002	[48]
Abrin	mice, intravenously human, inhalation human, oral	0.7 µg/kg 3.3 µg/kg 10-1000 µg/kg	0.0000007 0.0000033 0.00001-0.001
Maitotoxin	mouse, intraperitoneal	0.13 µg/kg	0.00000013	[49]
Polonium-210	human, inhalation	10 ng/kg (estimated)	0.00000001	[50]
Botulinum toxin (Botox)	human, oral, injection, inhalation	1 ng/kg (estimated)	0.000000001	[51]
Ionizing radiation	human, irradiation	6 Gy

Animal rights concerns

Animal-rights and animal-welfare groups, such as Animal Rights International,^[52] have campaigned against LD₅₀ testing on animals in particular as, 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 Organisation 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).

See also

• Animal testing
• Reed-Muench method

Other measures of toxicity

• IDLH
• Certain safety factor
• Therapeutic index
• Protective index
• Fixed Dose Procedure to estimate LD50
• Median toxic dose (TD50)
• Lowest published toxic concentration (TCLo)
• Lowest published lethal dose (LDLo)
• EC₅₀ (half maximal effective concentration)
• IC₅₀ (half maximal inhibitory concentration)
• Draize test
• Indicative limit value
• No-observed-adverse-effect level (NOAEL)
• Lowest-observed-adverse-effect level (LOAEL)
• Up-and-down procedure

Related measures

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

References

1. What is an LD50 and LC50
2. "Allergan Receives FDA Approval for First-of-Its-Kind, Fully in vitro, Cell-Based Assay for BOTOX® and BOTOX® Cosmetic (onabotulinumtoxinA)". Allergan Web site. 24 June 2011. Retrieved 2012-08-15.
3. "In U.S., Few Alternatives To Testing On Animals". Washington Post. 12 April 2008. Retrieved 2011-06-26.
4. REGISTRY OF TOXIC EFFECTS OF CHEMICAL SUBSTANCES (RTECS)
   COMPREHENSIVE GUIDE TO THE RTECS
5. Ernest Hodgson (2004). A Textbook of Modern Toxicology. Wiley-Interscience (3rd ed.).
6. "Material Safety Data Sheet Water MSDS". Section 11: Toxicological Information for the LD₅₀ verification.
7. Safety (MSDS) data for sucrose
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11. A.A. Babayan, A.V.Aleksandryan, "Toxicological characteristics of melamine cyanurate, melamine and cyanuric acid", Zhurnal Eksperimental'noi i Klinicheskoi Meditsiny, Vol.25, 345-9 (1985). Original article in Russian.
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14. Mecler, Francis J. (May 1981). Mammalian Toxological Evaluation of DIMP and DCBP (Phase 3 - IMPA) (Final report ed.). Litton Bionetics, Inc. The oral LD50 values for the test material, IMPA, were 7650 and 6070 mg/kg for male and female rats, respectively.
15. Safety (MSDS) data for sodium molybdate
16. Safety (MSDS) data for sodium chloride
17. Safety (MSDS) data for 4-acetamidophenol
18. LD50 values of THC in fischer rats
19. Archived July 11, 2015, at the Wayback Machine.
20. Frank T. Sanders, ed. (August 2006). Reregistration Eligibility Decision for Alkyl Dimethyl Benzyl Ammonium Chloride (ADBAC) (PDF) (Report). U.S. Environmental Protection Agency Office of Prevention, Pesticides, and Toxic Substances. p. 114. Retrieved 2009-03-31.
21. Coumarin Material Safety Data Sheet (MSDS)
22. Safety (MSDS) data for acetylsalicylic acid
23. Safety (MSDS) data for caffeine
24. "MATERIAL SAFETY DATA SHEET - Spent Metal Catalyst" (PDF). Archived from the original (PDF) on 2011-09-28.
25. Safety (MSDS) data for sodium nitrite
26. Chemical toxicity of uranium
27. DrugBank data for bisoprolol
28. Safety (MSDS) data for cobalt (II) chloride
29. Safety (MSDS) data for cadmium oxide
30. Sodium Fluoride MSDS
31. Pentaborane chemical and safety data
32. "Capsaicin Material Safety Data Sheet" (PDF). sciencelab.com. 2007. Retrieved 2007-07-13.
33. http://www.sigmaaldrich.com/catalog/DisplayMSDSContent.doc
34. Erowid LSD (Acid) Vault : Fatalities / Deaths. Erowid.org. Retrieved on 2013-07-17.
35. Safety (MSDS) data for arsenic trioxide
36. Safety (MSDS) data for metallic arsenic
37. Mayer B (January 2014). "How much nicotine kills a human? Tracing back the generally accepted lethal dose to dubious self-experiments in the nineteenth century". Archives of Toxicology 88 (1): 5–7. doi:10.1007/s00204-013-1127-0. PMC 3880486. PMID 24091634.
38. Safety (MSDS) data for sodium cyanide
39. "Hexachloroethane" (PDF). Retrieved 2014-01-03.
40. INCHEM: Chemical Safety Information from Intergovernmental Organizations: Strychnine.
41. Safety (MSDS) data for aflatoxin B1
42. Venomous Animals and their Venoms, vol. III, ed. Wolfgang Bücherl and Eleanor Buckley
43. LD50 for various snakes. Seanthomas.net. Retrieved on 2013-07-17.
44. EFSA - Scientific Opinion of the CONTAM Panel: Ricin (from Ricinus communis) as undesirable substances in animal feed [1] - Scientific Opinion of the Panel on Contaminants in the Food Chain. Efsa.europa.eu. Retrieved on 2013-07-17.
45. U.S. National Toxicology Program acute toxicity studies for Dioxin (2,3,7,8-TCDD)
46. Histochemical Demonstration of Calcium Accumulation in Muscle Fibres after Experimental Organophosphate Poisoning. Het.sagepub.com (1990-07-01). Retrieved on 2013-07-17.
47. Toxicity of the Organophosphate Chemical Warfare Agents GA, GB, and VX: Implications for Public Protection
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51. Fleming, Diane O.; Hunt, Debra Long (2000). Biological Safety: principles and practices. Washington, DC: ASM Press. p. 267. ISBN 1-55581-180-9.
52. Thirty-Two Years of Measurable Change

External links

• Canadian Centre for Occupational Health and Safety
• Lipnick, RL; Cotruvo, JA; Hill, RN; Bruce, RD; Stitzel, KA; Walker, AP; Chu, I; Goddard, M; Segal, L; Springer, J.A.; Myers, R.C. (1995). "Comparison of the up-and-down, conventional LD50, and fixed-dose acute toxicity procedures". Food and chemical toxicology 33 (3): 223–31. doi:10.1016/0278-6915(94)00136-C. PMID 7896233.