Therapeutic index

The ratio of the blood concentration at which a drug becomes toxic (TD50) and the concentration at which it is effective (ED50).

Dosage of drugs with a low therapeutic index can be challenging, as relatively small increases in drug levels can trigger side effects. Such drugs are said to have a small therapeutic window.

Therapeutic Index vs. Therapeutic Window (Quizlet, 2020)

The determination and interpretation of the therapeutic index in drug development (Nature Reviews Drug Discovery, 2012)

The Dose Makes the Poison (Science Translational Medicine, 2004)