Protective index
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 (
The protective index is similar to the
Protective index can also defined as 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.[1]
The higher the protective index, better is the antidotal value of a given substance. Sometimes the protective index is higher in the presence of two or more substances than in the presence of either of the substances alone. For example, the LD50 of potassium cyanide alone is 11 mg/kg, whereas it is 21 mg/kg in the presence of sodium nitrite, giving a protective index of 1.91. The LD50 of potassium cyanide in the presence of sodium thiosulfate is 35 mg/kg, giving a protective index of 3.2. The LD50 of potassium cyanide in the presence of both nitrite and thiosulfate is 52 mg/kg with a protective index of 4.73. Since the protective index is higher for the simultaneous use of nitrite and thiosulfate, the two chemicals constitute the antidote against cyanide intoxication.[1]
References
- ^ ISSN 1537-6516.