What is the Therapeutic Index (TI)?

The Therapeutic Index (TI) is an important parameter in assessing the safety of drugs. It is used to measure the relationship between the safety and effectiveness of a drug. The therapeutic index is typically calculated by comparing the minimum effective dose (MED) and the median lethal dose (LD50) of a drug, as follows:

Therapeutic Index (TI) = LD50/MED

Alternatively, sometimes the ratio of the LD50 to the median effective dose (ED50) is used to represent the therapeutic index:

Therapeutic Index (TI) = LD50/ED50

A higher therapeutic index indicates that a drug is safer because it means that the dose required to reach a toxic level is much higher than the dose required to produce a therapeutic effect. Conversely, if the therapeutic index is low, it suggests that the drug has a lower safety profile, as there is a smaller gap between the effective dose and the toxic dose, requiring more caution when using the drug.

In drug development and clinical application, the therapeutic index is an important reference indicator that helps doctors and pharmacologists assess the risks and benefits of a drug. However, it should be noted that the therapeutic index is not the only criterion for evaluating drug safety. Other factors such as the pharmacological properties of the drug, individual patient differences, and drug interactions should also be considered.