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A: The percentage of receptor occupancy resulting from full agonist (present at a single concentration) binding to receptors in the presence of increasing
concentrations of a partial agonist. Because the full agonist (filled squares) and the partial agonist (open squares) compete to bind to the same receptor
sites, when occupancy by the partial agonist increases, binding of the full agonist decreases. B: When each of the two drugs is used alone and response is
measured, occupancy of all the receptors by the partial agonist produces a lower maximal response than does similar occupancy by the full agonist. C:
Simultaneous treatment with a single concentration of full agonist and increasing concentrations of the partial agonist produces the response patterns
shown in the bottom panel. The fractional response caused by a single high concentration of the full agonist (filled squares) decreases as increasing
Source: Chapter 2. Drug Receptors & Pharmacodynamics, Basic & Clinical Pharmacology, 12e
concentrations of the partial agonist compete to bind to the receptor with increasing success; at the same time the portion of the response caused by the
Citation:
Masters while
SB, Trevor
AJ. response—ie,
Basic & Clinicalthe
Pharmacology,
12e; 2012
Available
at: http://mhmedical.com/
Accessed:
May 10,
partial agonist
(open Katzung
squares)BG,
increases,
the total
sum of responses
to the
two drugs
(filled triangles)—gradually
decreases,
2017
eventually reaching the value produced by partial agonist alone (compare with B).
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