Figure 1.

IC₅₀ : fC_max ratio calculations for verapamil and propafenone. (A) Typical hNa_v1.5 current recordings generated using an IonWorks™-based assay. Each individual recording shows data from a single well in response to vehicle (0.33% dimethyl sulphoxide, solid line) followed by a single concentration of verapamil (dotted line). Each recording is taken from the eighth pulse to 0 mV from a holding potential of −90 mV. (B) Graphs show concentration–effect curves for hNa_v1.5 channels generated using the same assay. The half maximal inhibitory concentration (IC₅₀) and maximal free plasma concentration in human (fC_max) values are also plotted. For propafenone, the hNa_v1.5 IC₅₀ is 1.2 µM and fC_max is 0.9 µM, giving a ratio (safety margin) of 1.3. For verapamil, the hNa_v1.5 IC₅₀ is 9.3 µM and the fC_max is 0.08 µM, giving a ratio of 115.