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The value of LD 50 for a substance is the dose required to kill half the members of a tested population after a specified test duration. LD 50 figures are frequently used as a general indicator of a substance's acute toxicity. A lower LD 50 is indicative of higher toxicity. The term LD 50 is generally attributed to John William Trevan. [2]
The lowest lethal dose (LD Lo) is the least amount of drug that can produce death in a given animal species under controlled conditions. [ 6 ] [ 7 ] The dosage is given per unit of bodyweight (typically stated in milligrams per kilogram ) of a substance known to have resulted in fatality in a particular species.
Revised values may follow in parentheses. N.D. Not determined. That is, the level is unknown, not non-existent. 10%LEL The IDLH value has been set at 10% of the lower explosive limit although other irreversible health effects or impairment of escape due to toxicology exist only at higher levels.
The ED50 is commonly used as a measure of the reasonable expectancy of a drug effect, but does not necessarily represent the dose that a clinician might use. This depends on the need for the effect, and also the toxicity. The toxicity and even the lethality of a drug can be quantified by the TD 50 and LD 50 respectively. Ideally, the effective ...
It is desirous for the value of LD 50 to be as large as possible, to decrease risk of lethal effects and increase the therapeutic window. In the above formula, TI safety increases as the difference between LD 50 and ED 50 increases—hence, a higher safety-based therapeutic index indicates a larger therapeutic window, and vice versa.
Quantitatively, it is the ratio given by the toxic dose divided by the therapeutic dose. A protective index is the toxic dose of a drug for 50% of the population (TD 50) divided by the minimum effective dose for 50% of the population (ED 50). A high protective index is preferable to a low one: this corresponds to a situation in which one would ...
The system is based on LD50 determination in rats, thus an oral solid agent with an LD50 at 5 mg or less/kg bodyweight is Class Ia, at 5–50 mg/kg is Class Ib, LD50 at 50–2000 mg/kg is Class II, and at LD50 at the concentration more than 2000 mg/kg is classified as Class III. Values may differ for liquid oral agents and dermal agents. [1]
For the drugs administered by oral and dermal route, the units of threshold dose are mg/kg body-weight/day (dose of the drug in mg per body weight in kg per day) or ppm (parts per million), while the threshold dose of drugs by inhalation delivery has the unit of mg/L 6h/day (amount of drug in mg in 1L of air, for 6 hours per day). [8]