waned in the 1940s with the arrival of new pesticides like DDT that were more durable. As of July 2015 it is not registered for pesticide use in the US, Europe, or Australia. It was introduced as anthelminthic in livestock in 1940 and is considered, with thiabendazole, to be the first modern anthelminthic. The first instances of resistance were noted in 1961. Among anthelmintics, Blizzard et al. 1990 found only paraherquamide to have similar activity to phenothiazine. It is possible that they share the same mode of action. Uses for this purpose in the US are still described but it has "virtually disappeared from the market." In the 1940s it also was introduced as antihelminthic for humans; since it was often given to children, the drug was often sold in chocolate, leading to the popular name, "worm chocolate." Phenothiazine was superseded by other drugs in the 1950s. Structure and synthesis The central C4SN ring is folded in phenothiazines. The compound was originally prepared by Bernthsen in 1883 via the reaction of diphenylamine with sulfur, but more recent syntheses rely on the cyclization of 2-substituted diphenyl sulfides. Few pharmaceutically significant phenothiazines are prepared from phenothiazine, although some of them are. Phenothiazines are electron donors, forming charge-transfer salts with many acceptors. References External links MSDS Hendricks, Christensen, J.B., and Kristiansen, Jette E. Sonderborg, Denmark. "Antibakterielle Eigenschaften der Phenothiazine: Eine Behandlungsoption für die Zukunft?" Chemotherapie Journal. 13.5. (2004): 203–205. Wissenschaftliche Verlagsgesesellschaft mbH. 21 August 2005. (PDF). PubChem Substance Summary: Phenothiazine National Center for Biotechnology Information. CDC - NIOSH Pocket Guide to Chemical Hazards