If the toxic dose to produce a response (TD50) is 25 mg and the dose for a desired effect (ED50) is 5 mg, the TI is 5.

If the toxic dose to produce a response (TD50) is 25 mg and the dose for a desired effect (ED50) is 5 mg, the TI is 5.

• A. TD50/ED50
• B. ED50/TD50
• C. TD50-ED50
• D. ED50+TD50

Answer: (A)

The main idea is the therapeutic index, which is defined as the ratio of the toxic dose to the effective dose (TD50/ED50). It expresses the safety margin between the dose that causes toxicity in 50% of people and the dose that produces the desired effect in 50%. Here, TD50 is 25 mg and ED50 is 5 mg. So TD50/ED50 = 25/5 = 5. This gives a TI of 5, meaning the toxic dose is five times the dose needed for the desired effect. A larger TI indicates a wider safety margin, while a smaller TI means the drug is riskier. Subtracting, adding, or taking the reciprocal of these values would not reflect the standard safety margin between efficacy and toxicity.

The main idea is the therapeutic index, which is defined as the ratio of the toxic dose to the effective dose (TD50/ED50). It expresses the safety margin between the dose that causes toxicity in 50% of people and the dose that produces the desired effect in 50%.

Here, TD50 is 25 mg and ED50 is 5 mg. So TD50/ED50 = 25/5 = 5. This gives a TI of 5, meaning the toxic dose is five times the dose needed for the desired effect. A larger TI indicates a wider safety margin, while a smaller TI means the drug is riskier. Subtracting, adding, or taking the reciprocal of these values would not reflect the standard safety margin between efficacy and toxicity.