What does the therapeutic index indicate?

The therapeutic index is a crucial pharmacological concept that quantifies the safety margin of a drug by comparing the dose that produces the desired therapeutic effect to the dose that causes toxicity. Specifically, it is defined as the ratio of the toxic dose (usually the dose at which 10% of the population experiences adverse effects) to the effective dose (typically the dose at which 50% of the population achieves the therapeutic effect). A higher therapeutic index indicates a greater safety margin, suggesting that there is a large difference between effective and toxic doses, making the drug safer for clinical use.

In this context, the therapeutic index does not measure the effectiveness of a drug directly, nor does it provide information about the potential for side effects or the duration of action within the body. Instead, it offers an essential insight into the balance between efficacy and safety, guiding clinicians in determining appropriate dosing regimens for patients.