TI reflects the safety margin between therapeutic and toxic doses.

TI reflects the safety margin between therapeutic and toxic doses.

• A. The margin between therapeutic and toxic doses
• B. The magnitude of therapeutic effect
• C. The rate of absorption
• D. The distribution volume

Answer: (A)

The therapeutic index is a measure of the safety margin between doses that provide therapeutic benefit and those that produce toxicity. It is typically expressed as a ratio like TD50/ED50 or LD50/ED50, so a larger value indicates a wider safety margin and a drug that is safer with respect to dose variability. This concept directly captures how close you are to toxic effects while still achieving the desired effect, which is why it’s the best description of the safety margin. The magnitude of the therapeutic effect describes efficacy, not safety; rate of absorption and distribution volume are pharmacokinetic properties that affect how the drug enters and moves through the body, not the balance between therapeutic and toxic doses.

The therapeutic index is a measure of the safety margin between doses that provide therapeutic benefit and those that produce toxicity. It is typically expressed as a ratio like TD50/ED50 or LD50/ED50, so a larger value indicates a wider safety margin and a drug that is safer with respect to dose variability. This concept directly captures how close you are to toxic effects while still achieving the desired effect, which is why it’s the best description of the safety margin. The magnitude of the therapeutic effect describes efficacy, not safety; rate of absorption and distribution volume are pharmacokinetic properties that affect how the drug enters and moves through the body, not the balance between therapeutic and toxic doses.