Median lethal dose curve of Neosaxitoxin (NeoSTX#5) formulation with and without bupivacaine. Remarkably, coinjection of bupivacaine in an extravascular (sciatic perineural) location does not worsen the systemic toxicity of NeoSTX in this model. NeoSTX-Bup = Neosaxitoxin-Bupivacaine; NeoSTX-Saline = Neosaxitoxin-saline.