What does LD-50 mean?

[Alfa]

What is LD-50?
LD stands for "Lethal Dose". LD50 is the amount of a material, given all at once, which causes the death of 50% (one half) of a group of test animals. The LD50 is one way to measure the short-term poisoning potential (acute toxicity) of a material.
Toxicologists can use many kinds of animals but most often testing is done with rats and mice. It is usually expressed as the amount of chemical administered (e.g., milligrams) per 100 grams (for smaller animals) or per kilogram (for bigger test subjects) of the body weight of the test animal. The LD50 can be found for any route of entry or administration but dermal (applied to the skin) and oral (given by mouth) administration methods are the most common.

What is LD-LO?
The lowest dose causing lethality. i.e. at this dose there is a risk of dying from a substance.

How does LD-50 relate to humans?
LD50 is not tested on humans. All relation to humans are only a guess. LD50 is only a ball park figure at best, so that lethal toxicity can be compared. Also, it says nothing about levels at which other acute toxic, but non-lethal, effects might occur.
LD50 is only useful for testing new drugs, to get a first indication on toxicity. But there are other far more humane methods for that. Like the Fixed Dose Procedure.

In general, the smaller the LD50 value, the more toxic the chemical is. The opposite is also true: the larger the LD50 value, the lower the toxicity.
The LD50 gives a measure of the immediate or acute toxicity of a chemical in the strain, sex, and age group of a particular animal species being tested. Changing any of these variables (e.g., type animal or age) could result in finding a different LD50 value. The LD50 test was neither designed nor intended to give information on long-term exposure effects of a chemical.

It is also important to know that the actual LD50 value may be different for a given chemical depending on the route of exposure (e.g., oral, dermal, inhalation). For example, some LD50s for dichlorvos, an insecticide commonly used in household pesticide strips, are listed below:

• Oral LD50 (rat): 56 mg/kg
• Dermal LD50 (rat): 75 mg/kg
• Intraperitoneal LD50: (rat) 15 mg/kg
• Inhalation LC50 (rat): 1.7 ppm (15 mg/m3); 4-hour exposure
• Oral LD50 (rabbit) 10 mg/kg
• Oral LD50 (pigeon): 23.7 mg/kg
• Oral LD50 (rat): 56 mg/kg
• Oral (mouse): 61 mg/kg
• Oral (dog): 100 mg/kg
• Oral (pig): 157 mg/kg

Differences in the LD50 toxicity ratings reflect the different routes of exposure. The toxicity rating can be different for different animals. The data above show that dichlorvos is much less toxic by ingestion in pigs or dogs than in rats.

The LD50 is only one source of toxicity information. For a more thorough picture of the immediate or acute toxicity of a chemical, additional information should be considered such as the lowest dose that causes a toxic effect (TDLO), the rate of recovery from a toxic effect, and the possibility that exposure to some mixtures may result in increasing the toxic effect of an individual chemical.

How can I use LD-50 in regards to drug consumption and assessing dangers?
You can't. Something with a LD-50 of 350mg may kill you at 200 mg or put you in a coma at a fraction of that amount.

Reputation Comments on this post:

nice breakdown, very clear and concise

[radiometer]

How can I use LD-50 in regards to drug consumption and assessing dangers?

The LD50 is useful for generating what is called the "therapeutic index" of a substance. This is expressed as the ratio between the LD50 and the minimum therapeutic dose of a substance. By comparing the therapeutic index of different drugs, one can judge their relative risks.

[jux]

LD01- Lethal dose for 1% of the animal test population
LD100- Lethal dose for 100% of the animal test population
TDLO- The lowest dose causing a toxic effect
(edit: i just realized you already mentioned TDLO and the LD's i mentioned are kind of obvious...oh well)

alternatives to the LD50 test (both methods predict lethal dose using fewer animals and are being considered as replacements to the ld50 test):

FDP (fixed dose procedure)
ATC (acute-toxic-class)