Displacement of ³H-etomidate by etomidate analogs (A) and metabolites (B). ³H-etomidate (2 nM) and the desired concentration of etomidate analog or metabolite were equilibrated with membranes. The mixture was then filtered, and radioactivity was measured in the washed filter. Each data point is the mean ± SD (n = 3) radioactivity measured in the washed filter. The curves are fits of each data set to a competitive binding equation yielding half-inhibitory concentrations (IC₅₀s) of 143 nM (cyclopropyl methoxycarbonyl metomidate [CPMM]), 50 µM (carboetomidate), 1.1 mM (etomidate-CA), and 0.27 mM (CPMM-CA). (A) Data for etomidate are shown for comparison (IC₅₀: 26 nM). (B) The fits obtained for the parent sedative-hypnotics (i.e., etomidate and CPMM) are shown for comparison. The final protein concentration was 0.07 mg/ml. CPM = counts per minute.