(known simply as efficacy
) is the upper limit of the dose-response relationship
on the response axis of the graph shown below. Accordingly, drugs A, C, and D have equal efficacy, while all have greater efficacy than drug B.
in a patient may be determined by the mode of interactions of the drug with the receptor
(as with partial agonists), or by characteristics of the receptor-effector system
(e.g., diuretics acting on one portion of the nephron may produce a much greater diuretic effect than the diuretics that act on other parts of the nephron); therapeutic efficacy
in a patient also depends on a host of other factors.
The practical clinical efficacy
of a drug may in some cases be limited by the drug’s tendency to cause a toxic effect
, even if the drug can otherwise exert a greater therapeutic effect.