AMG-517, a potent and selective vanilloid receptor (VR1) antagonist, was in clinical trials with Amgen for the treatment of pain. AMG 517 inhibits CAP- (500 nM), acid- (pH 5.0), or heat-(45 °C) induced 45Ca2+ influx into human TRPV1-expressing CHO Cells with IC50 of 0.76 nM, 0.62 nM and 1.3 nM. AMG-517 blocks capsaicin-, proton-, and heat-induced inward currents in TRPV1-expressing cells similarly. AMG-517 inhibits native TRPV1 activation by capsaicin in rat dorsal root ganglion neurons with an IC50 value of 0.68 nM. Oral administration of AMG-517 produces a dose-dependent increase in plasma concentrations, it also produces a dose-dependent decrease in the number of flinches induced by capsaicin treatment. The minimally effective dose (MED), based on a statistically significant difference in number of flinches from the vehicle versus capsaicin-administered group, is 0.3 mg/kg for AMG 517. The corresponding plasma concentrations are 90 to 100 ng/mL for AMG-517. AMG-517 (3 mg/kg) exhibits significant reductions in capsaicin-induced flinch up to 24 h after dosing. AMG 517 blocks thermal hyperalgesia in CFA model of pain. Unfortunately, clinical studies of AMG-517 were discontinued due to the hyperthermia observed after exposure to single and multiple doses.