PHARM/PCS V5 · Procedure 13 Receptor Pharmacology
Dissociation Constant II: Partial Agonists
Estimate a partial agonist's dissociation constant Kp by comparing its equieffective concentrations with those of a full agonist.
What it computes
Determines the dissociation constant Kp of a partial agonist by comparing its equieffective concentrations P with those of a strong agonist A. A double-reciprocal plot of 1/A vs. 1/P gives Kp = slope / intercept.
Inputs and outputs
You provide
- Equieffective pairs: the partial agonist concentration P and the full agonist concentration A, one pair per line
PHARM/PCS reports
- The fitted double-reciprocal line, slope and intercept
- Kp, in the concentration units of your data
- The double-reciprocal plot of 1/A against 1/P
When to use it
When the drug of interest is a partial agonist and you want its receptor affinity, using a strong (full) agonist as the reference. It's the partial-agonist companion to the full-agonist method in Procedure 12.
Reading the results
The estimate depends on genuinely equieffective A/P pairs: the strong agonist and partial agonist must be producing the same effect at each paired point. Because Kp is a ratio of slope to intercept, small errors in either propagate, so treat a Kp from a poorly fit line skeptically.
Units follow your data
Kp inherits the concentration units you enter, molar in the book example. Because Kp is the ratio of slope to intercept, an error in either one carries straight through, so check the fit before quoting the value.
This page describes the procedure. Calculations run inside the licensed PHARM/PCS V5 application. PHARM/PCS is a trademark of MCS Scientific LLC.