Where is the therapeutic index of a drug listed?

Answer 1

Having worked in the pharma industry in senior positions in clinical drug development for 30 years, the therapeutic index of a drug is essentiallya qualitative concept of risk:benefit ratio for one drug vs another and is NOT a real number. There is no agreed upon formula for computing the therapeutic index of a drug using clinical results. The reason the formula does not exist is that it would require a consensus agreement among experts for each disease regarding the definition of a clinical response (patients usually show graded responses, not simply full response or no response) and a consensus definition of the clinical toxicity of a drug. For example, if a medication produces side effects consisting of dose-dependent increases in blood pressure, decreases in white blood cell counts and vomiting--what criteria shall be selected for a toxic risk? In animal studies. the ratio of LD50/ED50 (dose in a species that kills one half of the animals divided by the dose that is effective in the disease model in one half of the test animals) is sometimes computed and can be helpful in deciding which of several potential drug candidates is to be selected for development. It is probably possible to find in select publications, sufficient information to compute a therapeutic index that compares several drugs using a uniform definition of the dose needed to produce the same therapeutic benefit and the dose needed (on average) to produce a side effect of sufficient severity to qualify as a dose-limiting problem. Even in this case, the therapeutic index would be essentially an ad hoc determination produced by the author or reviewer. It would likely not be regarded by others as the therapeutic index for the drugs assessed because other experts would likely employ a different definition of side effects of concern.