Therapeutic index of a drug signifies: September 2005
**Core Concept**
The therapeutic index (TI) of a drug is a quantitative measure of its relative safety and efficacy. It is calculated as the ratio of the dose that produces a therapeutic effect to the dose that produces toxicity. The TI is a crucial parameter in pharmacology, as it helps in assessing the safety margin of a drug.
**Why the Correct Answer is Right**
The TI is calculated by dividing the dose of the drug that produces a desired therapeutic effect (ED50) by the dose that produces a toxic effect (LD50). This ratio provides an indication of the drug's safety margin. For example, a drug with a high TI is considered safer, as it can be administered at a higher dose without causing toxicity. The TI is an important consideration in the development and use of medications, as it helps in minimizing the risk of adverse effects.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the TI is not a measure of a drug's efficacy. While a high TI indicates a safer drug, it does not necessarily imply that the drug is more effective.
**Option B:** This option is incorrect because the TI is not solely a measure of a drug's toxicity. The TI takes into account both the therapeutic and toxic effects of the drug.
**Option C:** This option is incorrect because the TI is not a measure of a drug's potency. While a high TI may indicate a more potent drug, the TI is not a direct measure of potency.
**Clinical Pearl / High-Yield Fact**
A high TI is not always a guarantee of safety, as it may indicate that the drug has a narrow therapeutic window, where small increases in dose can lead to significant toxicity.
**Correct Answer:** B. The therapeutic index of a drug signifies the ratio of the dose that produces a therapeutic effect to the dose that produces toxicity.