Protective index: Difference between revisions

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Revision as of 14:00, 28 January 2024

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The '''protective index''' ('''PI''') is a comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes toxicity. 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 ([[TD50|TD₅₀]]) divided by the minimum effective dose for 50% of the population ([[ED-50|ED₅₀]]). A high protective index is preferable to a low one: this corresponds to a situation in which one would have to take a much higher dose of a drug to reach the toxic threshold than the dose taken to elicit the therapeutic effect. A drug should ordinarily only be administered if the protective index is greater than one, indicating that the benefit outweighs the risk.

<math>\mbox{Protective index} = \frac{\mathrm{TD}_{50}}{\mathrm{ED}_{50}}</math>

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The protective index is similar to the [[therapeutic index]], but concerns toxicity ([[TD50|TD₅₀]]) rather than lethality ({{LD50}}); thus, the protective index is a smaller ratio. Toxicity can take many forms, as drugs typically have multiple side effects of varying severity, so a specific criterion of toxicity must be specified for the protective index to be meaningful. Ideally a choice is made such that the harm caused by the toxicity just outweighs the benefit of the drug's effect. Thus, the protective index is a more accurate measure of the benefit-to-risk ratio than the therapeutic index, but is less objectively defined. Nevertheless, the therapeutic index can be viewed as an [[upper bound]] to the protective index for a given substance.

Protective index referscan toalso defined as the factor by which the

{{Pharmacology}}

'''Protective Index'''

Protective index refers to the factor by which the

dose of a toxicant must be multiplied to produce a

defined level of toxicity in the presence of a nontoxic

dose of another chemical^{^{Bhat et al., 2007}}.

''''<math>\mbox{Protective index} = LD50 \frac{\mathrm{LD}_{50}\text{of A with B/LD50 }}{\mathrm{LD}_{50}\text{of A alone''''}}</math>

The higher the protective index, better is the

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a protective index of 3.2. The LD50 of potassium

cyanide in the presence of both nitrite and thiosulfate

is 52&nbsp;mg/kg with a protective index of 4.73 .

Since the protective index is higher for the simultaneous use of nitrite and thiosulfate, the

the simultaneous use of nitrite and thiosulfate, the

two chemicals constitute the antidote against cyanide

intoxication.

Bhat, A Shakoor and Ahanger, Azad A, 2007. Toxicology Mechanisms and Methods, 17:441–450, 2007

{{Pharmacology}}

[[Category:Clinical pharmacology]]