IC50 of duloxetine for the resting and inactivated wild-type hNav1.7 Na+ channel were 22.1+/-0.4 and 1.79+/-0.10 microM, respectively (mean+/-SE, n=5).?The IC50 for the open Na+ channel was 0.25+/-0.02 microM (n=5), as determined by the block of persistent late Nav1.7 Na+ currents.?Similar open-channel block by duloxetine was found in the muscle Nav1.4 isoform (IC50=0.51+/-0.05 microM;?n=5).?Block by duloxetine appeared via the conserved local anesthetic receptor as determined by site-directed mutagenesis.?Finally, duloxetine elicited strong use-dependent block of neuronal transient Nav1.7 Na+ currents during repetitive stimulations[1].