PHARM/PCS V5 · Procedure 16 Receptor Pharmacology
pA2 Analysis II: Time-Dependent Method
Estimate pA2 from a single antagonist concentration by following the agonist dose ratio as the antagonist washes out, and get its half-life as well.
What it computes
Determines pA2 from a single antagonist concentration by tracking the agonist dose-ratio over time as both agents decay. The regression of log(A′/A − 1) against time yields the pA2 from the intercept and the antagonist elimination half-life from the slope.
Inputs and outputs
You provide
- Time and the agonist dose ratio A′/A, one pair per line
- The starting antagonist concentration B0
PHARM/PCS reports
- Regression slope and intercept
- pA2, from the intercept
- The antagonist's elimination half-life, from the slope
- A plot of the dose-ratio term against time, with the fitted line
When to use it
When you can't easily run several antagonist concentrations but can follow one concentration's effect as it washes out, a practical alternative to the classic Schild plot (Procedure 15) that also hands you the antagonist's half-life.
Reading the results
It trades multiple concentrations for a time series, so it assumes the antagonist declines by simple first-order kinetics and the agonist's action is stable across the window. Drift in the preparation over time contaminates both pA2 and half-life, so cross-check against a Schild estimate (Procedure 15 or 17) when you can.
Two results from one run
The half-life comes with the pA2: the slope gives the elimination rate constant, exactly as the 1986 program reported it. The method assumes the antagonist declines by simple first-order kinetics and that the preparation stays stable across the window.
This page describes the procedure. Calculations run inside the licensed PHARM/PCS V5 application. PHARM/PCS is a trademark of MCS Scientific LLC.