LD50 /ED50 is -

Ans. is 'a' i.e.. Therapeutic index Therapeutic index o Drugs usually have more than one action. o The maximal response for the different action of a drug may be different ie the DRCs (Dose response curves) for different effects of a drug may be different. o The extent of separation of DRCs of a drug for different effects is a measure of its selectivity, e.g. the DRCs for bronchodilatation and cardiac stimulation are quite similar in case of isoprenaline but far apart in case of salbutamol - the latter is more selective. o The gap between the therapeutic effect DRC and the adverse effect DRC defines the safety margin or the therapeutic index. o In Experimental animals Therapeutic index = Median lethal dose (Ld50) ------------ Median effective dose (Ed50) o But in clinical set up, the therapeutic range is bounded by the dose w hich produces minimal therapeutic effect and the dose which produces maximal acceptable adverse effect. "Therapeutic index is the ratio between the toxic dose and the therapeutic dose of a drug, and is used as a measure of the relative safety of the drug for a particular treatment "