What is indicated by a "therapeutic index"?

A "therapeutic index" is defined as the margin of safety of a drug, specifically comparing the toxic dose to the therapeutic dose. It is a crucial concept in pharmacology that helps clinicians evaluate the safety of a drug. A drug with a high therapeutic index has a wide safety margin, meaning there is a significant difference between the dose that produces the desired therapeutic effect and the dose that causes adverse effects. This knowledge is vital for determining appropriate dosage regimens and minimizing the risk of toxicity in patients.

In contrast, the time it takes for a drug to show effects does not pertain to the therapeutic index, as it relates to the onset of action rather than the safety margin. Similarly, measuring a drug's effectiveness in clinical trials is more about determining how well a drug works rather than its safety profile. Lastly, the percentage of patients who respond to drug therapy relates to its efficacy rather than the relationship between toxic and therapeutic doses, which is what the therapeutic index specifically addresses.