What is the therapeutic index?

What is the therapeutic index?

• A. Onset of action
• B. Peak level
• C. Ratio of toxic dose to therapeutic dose
• D. ED50

Answer: (C)

The therapeutic index is a measure of drug safety that compares how much drug is needed to produce a toxic effect with how much is needed to achieve the desired therapeutic effect. It’s typically expressed as the ratio of the toxic dose (TD50) to the therapeutic dose (ED50). A larger ratio means a wider safety margin, meaning you can dose a drug with less risk of toxicity relative to its beneficial effect. If the ratio is small, the drug has a narrow safety margin and dosing must be more tightly controlled. ED50 is the dose that produces the desired effect in 50% of people and is part of the calculation, but the index itself is the toxic-to-therapeutic dose ratio. Onset of action refers to how quickly the drug starts working, and peak level relates to the highest concentration achieved, which are different concepts.

The therapeutic index is a measure of drug safety that compares how much drug is needed to produce a toxic effect with how much is needed to achieve the desired therapeutic effect. It’s typically expressed as the ratio of the toxic dose (TD50) to the therapeutic dose (ED50). A larger ratio means a wider safety margin, meaning you can dose a drug with less risk of toxicity relative to its beneficial effect. If the ratio is small, the drug has a narrow safety margin and dosing must be more tightly controlled. ED50 is the dose that produces the desired effect in 50% of people and is part of the calculation, but the index itself is the toxic-to-therapeutic dose ratio. Onset of action refers to how quickly the drug starts working, and peak level relates to the highest concentration achieved, which are different concepts.