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.
(2) an interference, such as antagonism with another drug
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Specialty: Pharmacology, clinical