Overview Therapeutic index (TI) measurement of drug safety refers to the relationship between toxic and therapeutic dosing TI = TD50/ED50 therapeutic index of a drug is the ratio of the dose that produces toxicity to the dose that produces a clinically desired or effective response TD50 = the dose of drug that causes a toxic response in 50% of the population ED50 = the dose of drug that is therapeutically effective in 50% of the population a safer drug has a higher therapeutic index very large lethal dose, very small effective dose a more dangerous drug has a lower therapeutic index may require regular monitoring of drug levels examples include: login to view 8 more bullets Therapeutic drug monitoring therapeutic window (TW) is the range of drug concentrations in which a drug is effective Therapeutic Window TW concept is reflected in TI calculation TW = MTC/MEC login to view 3 more bullets