Saxitoxin (STX) is a cyanotoxin found in marine dinoflagellates (algae). It is a neurotoxin that's a selective sodium channel blocker. The United States military isolated saxitoxin and assigned it the chemical weapon designation TZ. It is almost unique among toxins in that it acts very quickly, in a matter of minutes. The median lethal concentration (LCt50) of TZ is 5 mg·min/m³. The medical importance of saxitoxin is in relation to red tide in shellfish and causes the paralytic sh… (More on Saxitoxin)