Some drugs encounter a "ceiling effect" as the administered dose increases.


A drug that displays a ceiling effect has a dose-dependent increase in activity up to a certain point after which no further effect is observed with an increase in dose. This plateau cannot be overcome by increasing the dose.


Possible explanations of the ceiling effect:

(1) saturation of a limited number of receptors

(2) the inactive drug is converted to an active metabolite by a metabolic pathway that operates at a fixed rate



(1) There is no benefit to increasing a dose once the ceiling has been reached.

(2) A further increase in dose increases the risk for adverse drug effects.

(3) A further increase in dose costs more for no benefit.


Differential diagnosis:

(1) noncompliance

(2) an interference, such as antagonism with another drug


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