Therapeutic index of a drug is an indicator of:-

Therapeutic index (T.I) = LD 50 / ED 50 = Median lethal dose / Median effective dose Median lethal dose: dose at which 50% of animals die after receiving drug. Median effective dose: dose at which 50% of patient see effect after receiving the drug LD50 should be high, i.e. The drug should produce toxicity at high doses. (not at low dose) ED50 should be low, i.e. The drug should produce effects at even low dose (i.e. Potent) :- Ti l/e - Drug potency is a choosing factor in dose of drug & efficacy is for choice of drug.