Which statement about TI is false?

Which statement about TI is false?

• A. A wide TI means a large safety margin between ED50 and TD50.
• B. TI is used to assess safety margins of drugs.
• C. A small TI indicates a very large safety margin.
• D. A large TI correlates with higher safety margin.

Answer: (C)

Therapeutic index contrasts the dose that produces toxicity with the dose that produces the desired effect. It’s a way to gauge safety, calculated as TD50 (toxic) or LD50 (lethal) divided by ED50 (effective). A larger index means you can give a bigger dose before reaching toxic levels, so the drug has a wider safety margin. A smaller index means the toxic level is close to the effective level, giving a narrow safety margin and higher risk of toxicity at therapeutic doses. The statement that a small TI indicates a very large safety margin is not correct. A small TI actually indicates a narrow safety margin, meaning the therapeutic range is close to the toxic range. The other statements align with this concept: a wide TI corresponds to a large safety margin, TI is used to assess safety margins, and a large TI correlates with higher safety margin.

Therapeutic index contrasts the dose that produces toxicity with the dose that produces the desired effect. It’s a way to gauge safety, calculated as TD50 (toxic) or LD50 (lethal) divided by ED50 (effective). A larger index means you can give a bigger dose before reaching toxic levels, so the drug has a wider safety margin. A smaller index means the toxic level is close to the effective level, giving a narrow safety margin and higher risk of toxicity at therapeutic doses.

The statement that a small TI indicates a very large safety margin is not correct. A small TI actually indicates a narrow safety margin, meaning the therapeutic range is close to the toxic range. The other statements align with this concept: a wide TI corresponds to a large safety margin, TI is used to assess safety margins, and a large TI correlates with higher safety margin.