ED50 and LD50

ED50 (effective dose)

It is related to dose. It is also called a median response. It is defined as a dose at which drugs show 50 % of its maximum response.

LD50 (lethal dose)

It is related to percentage of the population. It is defined as the concentration of a drug that causes the death of a 50 % test population.


Lethal: Term used in the case of animals.
Toxic: Term used in the case of humans.

Therapeutic window

Dose at which drug shows maximum response but there is no observable toxic effect. It has two types
  1. The therapeutic window narrows.
  2. Therapeutic window is wider. 



Therapeutic index (T.I)

It is the ratio of LD50 to ED50
                                      
                                     LD50
                           T.I = ---------
                                     ED50
Note: High T.I is good. It means a high margin of safety and vice versa.

Potency

Amount of a drug that is needed to produce a required effect (response). It is related to dose (depends upon dose).

Efficacy

It means the maximum  effect. It is independent of dose.




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