Therapeutic Index

The therapeutic index (TI) is an indicator that is used to assess the safety and effectiveness of drugs. It characterizes the breadth of the therapeutic effect of a drug and is expressed as the ratio of the average lethal dose (LD50) to the dose that causes a therapeutic effect in half of the experimental animals (ED50).

The higher the TI, the safer the drug is. If the TI is low, this may mean that the dose required to produce a therapeutic effect may be too high and cause side effects.

To assess TI, a method is used to determine LD50 and ED50 in experimental animals such as mice, rats or rabbits. The ratio between these two measures is then calculated.

For example, if the LD50 is 100 mg/kg and the ED50 is 20 mg/kg, then the TI will be 5. This means that to achieve a therapeutic effect, a dose of 5 times less is required than to achieve a fatal outcome.

TI is important when choosing a drug to treat a specific disease. If a drug has a low TI, its use may be limited due to the high risk of side effects. If the TI is high, then the drug can be used in higher doses and cause fewer side effects.

In general, TI is an important indicator of the safety and effectiveness of a drug, which allows one to assess its breadth of action and potential risk to patient health.