Quoted from Wikipedia
Therapeutic index (also known as therapeutic ratio) is a comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes death (in animal studies) or toxicity (in human studies).[1]
Quantitatively, it is the ratio given by the lethal or toxic dose divided by the therapeutic dose.
In animal studies, the therapeutic index is the lethal dose of a drug for 50% of the population (LD50) divided by the minimum effective dose for 50% of the population (ED50).
Lethality is not determined in human clinical trials; instead, the dose that produces a toxicity in 50% of the population (TD50) is used to calculate the therapeutic index.
While the lethal dose is important to determine in animal studies, there are usually severe toxicities that occur at sublethal doses in humans, and these toxicities often limit the maximum dose of a drug. A higher therapeutic index is preferable to a lower one: a patient would have to take a much higher dose of such a drug to reach the lethal/toxic threshold than the dose taken to elicit the therapeutic effect.
Pharmacovigilance (abbreviated PV or PhV), also known as Drug Safety, is the pharmacological science relating to the collection, detection, assessment, monitoring, and prevention of adverse effects with pharmaceutical products.[1] The etymological roots for the word "pharmacovigilance" are: pharmakon (Greek for drug) and vigilare (Latin for to keep watch). As such, pharmacovigilance heavily focuses on adverse drug reactions, or ADRs, which are defined as any response to a drug which is noxious and unintended, including lack of efficacy, which occurs at doses normally used for the prophylaxis, diagnosis or therapy of disease, or for the modification of physiological function. Medication errors such as overdose, and misuse and abuse of a drug, are also of interest because they may result in an ADR.[2]