Noun
therapeutic index (plural therapeutic indexes or therapeutic indices)
(pharmacology) The ratio of the median toxic dose of a drug to its median effective dose, used to gauge the safety of a particular medication (a low therapeutic index indicates that the drug is easily overdosed).
A compound with a narrow therapeutic index (close to one) exerts its desired effect at a dose close to its toxic dose. Source: Internet
A compound with a wide therapeutic index (greater than five) exerts its desired effect at a dose substantially below its toxic dose. Source: Internet