In
toxicology
Toxicology is a scientific discipline, overlapping with biology, chemistry, pharmacology, and medicine, that involves the study of the adverse effects of chemical substances on living organisms and the practice of diagnosing and treating e ...
, the median toxic dose (TD
50) of a drug or toxin is the dose at which
toxicity
Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subs ...
occurs in 50% of cases. The ''type'' of toxicity should be specified for this value to have meaning for practical purposes. The median toxic dose encompasses the category of toxicity that is greater than
half maximum effective concentration (ED
50) but less than the median lethal dose (LD
50). However, for some highly potent toxins (ex.
lofentanil,
botulinum toxin
Botulinum toxin, or botulinum neurotoxin (BoNT), is a neurotoxic protein produced by the bacterium ''Clostridium botulinum'' and related species. It prevents the release of the neurotransmitter acetylcholine from axon endings at the neurom ...
) the difference between the ED
50 and TD
50 is so minute that the values assigned to them may be approximated to equal doses. Since toxicity need not be lethal, the TD
50 is generally lower than the
median lethal dose
In toxicology, the median lethal dose, LD50 (abbreviation for " lethal dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a toxic unit that measures the lethal dose of a toxin, radiation, or pathogen. The value of LD50 for a substance is ...
(LD
50), and the latter can be considered an
upper bound
In mathematics, particularly in order theory, an upper bound or majorant of a subset of some preordered set is an element of that is greater than or equal to every element of .
Dually, a lower bound or minorant of is defined to be an eleme ...
for the former. However, since the toxicity is above the effective limit, the TD
50 is generally greater than the ED
50. If the result of a study is a toxic effect that does not result in death, it is classified as this form of toxicity.
Toxic effects can be defined differently, sometimes considering the therapeutic effect of a substance to be toxic (such as with
chemotherapeutics) which can lead to confusion and contention regarding a substance's TD
50. Examples of these toxic endpoints include cancer, blindness, anemia, and birth defects.
References
*
Toxicology
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