LD50 also known as the "Median Lethal Dose" is the estimated dose of a substance required to kill half the members of a tested population after a specified test. They were typically carried out in at least 2 species of animals (a rodent and non rodent species) using the methods of administration most likely to be used clinically (or recreationally)
It differs from other LD values such as LDLo which is the lowest dose recorded to kill a member of the population.
When these meausures are given they should be followed by the species in which the test was carried out and the method of administration as these can have rather large impacts on the value.
In more recent times the use of LD50 has been seen as unethical and the usefulness of this data has been questioned. These values fail to recognise the often more likely and more important non-lethal or long-term toxic effects. Because of this it has been largely abandoned as a measure of toxicity.
More recently measures of toxicity taken include the following:
- No toxic effect level (NTEL): The largest dose at which there is no observed toxic effects in the most sensitive species
- No Observed adverse effect level (NOAEL): Largest Dose causing no obverved tissue toxicity or undesirable physiological effects.
- Maximum tolerated dose (MTD): The largest dose at which there are no obvious signs of toxcity or ill health
- No observed effect level (NOEL): The threshold dose which causes any observed pharmacological or toxic effect.