Question

The therapeutic index is defined as _______

• A. \(LD_{50}/ED_{50}\)
• B. \(ED_{50}/LD_{50}\)
• C. \(Dose/Time\)
• D. \(Clearance/Volume\)

Hint:

Therapeutic index \(= LD_{50}/ED_{50}\). Higher therapeutic index means greater safety margin.

Answer 1

The Correct Option is A

The therapeutic index is a critical concept in pharmacology, used to assess the safety of a drug. It is defined as the ratio of the dose that produces toxicity to the dose that produces a therapeutic effect. This is mathematically expressed as:

\(Therapeutic \, Index = \frac{LD_{50}}{ED_{50}}\)

Where:

• \(LD_{50}\) (Lethal Dose, 50%) is the dose of the drug that is lethal to 50% of a population
• \(ED_{50}\) (Effective Dose, 50%) is the dose of the drug that produces the desired therapeutic effect in 50% of a population

This ratio is an important indicator of a drug's safety margin. A higher therapeutic index indicates a greater margin of safety, meaning there is a larger gap between the effective dose and the lethal dose. Conversely, a lower therapeutic index suggests a smaller safety margin.

Let's review the options and determine why \(\frac{LD_{50}}{ED_{50}}\) is the correct answer:

1. \(\frac{LD_{50}}{ED_{50}}\): This is the correct definition of the therapeutic index and is widely accepted in pharmacology.
2. \(\frac{ED_{50}}{LD_{50}}\): This is incorrect because it inverts the ratio, which does not represent the therapeutic index.
3. \(\frac{Dose}{Time}\): This describes a rate of dosage over time, not the therapeutic index.
4. \(\frac{Clearance}{Volume}\): This pertains to pharmacokinetics, specifically the rate at which a drug is removed from the body per unit volume, not the therapeutic index.

Thus, the therapeutic index is correctly defined as \(\frac{LD_{50}}{ED_{50}}\).

This concept is vital in drug development and clinical pharmacy to ensure the safe use of therapeutic agents.