What is the correct expression for TI?

What is the correct expression for TI?

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

Answer: (D)

The key idea is the therapeutic index, a measure of safety that compares the dose causing toxicity to the dose that produces the desired therapeutic effect. It is defined as the ratio TD50/ED50, the amount that causes toxicity in 50% of individuals divided by the amount that produces therapeutic effect in 50%. This ratio shows how much larger the toxic dose is relative to the effective dose: a higher TI means a wider safety margin. For example, if the ED50 is 10 mg and the TD50 is 1000 mg, the TI is 100, indicating you can reach the therapeutic effect far below the level that would cause toxicity. Expressions like TD50 minus ED50 or TD50 times ED50 don’t quantify how much safer one dose is than the other, and subtracting or multiplying doses isn’t a meaningful measure of safety. (Sometimes LD50/ED50 is used in place of TD50/ED50, depending on terminology.)

The key idea is the therapeutic index, a measure of safety that compares the dose causing toxicity to the dose that produces the desired therapeutic effect. It is defined as the ratio TD50/ED50, the amount that causes toxicity in 50% of individuals divided by the amount that produces therapeutic effect in 50%. This ratio shows how much larger the toxic dose is relative to the effective dose: a higher TI means a wider safety margin. For example, if the ED50 is 10 mg and the TD50 is 1000 mg, the TI is 100, indicating you can reach the therapeutic effect far below the level that would cause toxicity. Expressions like TD50 minus ED50 or TD50 times ED50 don’t quantify how much safer one dose is than the other, and subtracting or multiplying doses isn’t a meaningful measure of safety. (Sometimes LD50/ED50 is used in place of TD50/ED50, depending on terminology.)