Question

Choose the true statement(s) about therapeutic index (TI). Select all that apply.
a. A drug with a high therapeutic index would be effective above the dose at which it is potentially toxic.
b. A narrow TI is preferable.
c. A drug for which the maximum safe dose is close to the minimum effective dose would have a high TI.
d. It is one measure of a drug’s general safety.
e. A drug that is not selectively toxic would most likely have a high TI.

Accepted Answer

Step 1: Understand the definition of Therapeutic Index (TI). TI is a ratio that compares the toxic dose of a drug to its effective dose, usually expressed as $$TI = \frac{TD_{50}}{ED_{50}}$$, where $$TD_{50} is $$the dose that causes toxicity in 50% of the population, and $$ED_{50} is $$the dose that produces the desired effect in 50% of the population. Step 2: Analyze statement (a): "A drug with a high therapeutic index would be effective above the dose at which it is potentially toxic." Since a high TI means the toxic dose is much higher than the effective dose, the drug is effective at doses well below toxic levels, so this statement is false. Step 3: Analyze statement (b): "A narrow TI is preferable." A narrow TI means the effective dose and toxic dose are close, which increases risk; therefore, this statement is false because a wide TI is generally preferable for safety. Step 4: Analyze statement (c): "A drug for which the maximum safe dose is close to the minimum effective dose would have a high TI." If the safe dose is close to the effective dose, the TI is low, so this statement is false. Step 5: Analyze statements (d) and (e): Statement (d) says TI is a measure of a drug’s general safety, which is true because TI indicates the margin between effective and toxic doses. Statement (e) says a drug that is not selectively toxic would most likely have a high TI; lack of selective toxicity usually means higher toxicity to host cells, so TI would be low, making this statement false.

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Concetti chiave

Therapeutic Index (TI)

Selective Toxicity

Safety and Efficacy in Drug Dosing