Neosaxitoxin is a site-1 specific sodium channel blocker which acts synergistically with local anesthetics to provide surgical anesthesia by peripheral nerve blocks or local infiltration and markedly increases the duration of post-operative analgesia. Saxitoxin and neosaxitoxin, small molecules synthesized by marine dinoflagellates and freshwater cyanobacteria. Neosaxitoxin, one of the saxitoxin analogs, differs from saxitoxin by the addition of one oxygen atom, wherein the hydrogen (-H) at Nitrogen 1 in saxitoxin is replaced by a hydroxyl group (-OH) in neosaxitoxin. Neosaxitoxin has shown greater potency than saxitoxin and its analogs and is also more potent than tetrodotoxin in in vitro and in vivo animal studies.Neosaxitoxin showed an effective local anesthetic effect when injected in the subcutaneous plane. The efficacy of a 50-ug dose of neosaxitoxin was shown. Neosaxitoxin has poor affinity for the cardiac isoform of the sodium channel and does not cross the blood–brain barrier, thus this compound is virtually devoid of cardiac and central nervous system toxicity—the limiting toxicities of traditional local anesthetics.