Therapeutic Index

The therapeutic index of a drug is the ratio of the dose that is toxic in 50% of the population to the dose that is effective in 50%.

The therapeutic index of a drug provides a range of effective and toxic doses.

An anticoagulant agent like warfarin has a narrow therapeutic index window for achieving the desired anticoagulation effect. However, within the effective dose range, some individuals may experience hemorrhage due to the overlapping toxic dose.

Drugs with a large therapeutic index value are considered safe since their effective and toxic concentrations are farther apart.

For such drugs, a dose higher than the minimum required to achieve the desired effect may be administered.

In summary, although a high therapeutic index may indicate relative safety, a smaller margin suggests potential toxic effects. The therapeutic index, as an indicator of a drug’s safety, has limitations since the data relies on animal toxicity studies, which may not precisely reflect the toxic effects experienced in humans.