(both chemists within the Chemical Development Laboratories at Burroughs Wellcome Co., Research Triangle Park, NC) in collaboration with John J. Savarese MD (who at the time was an anesthesiologist in the Dept. of Anesthesia, Harvard Medical School at the Massachusetts General Hospital, Boston, MA). Specifically, mivacurium was first synthesized in 1981. Early structure-activity studies had confirmed that the bulky nature of the "benzylisoquinolinium" entity provided a non-depolarizing mechanism of action. Partial saturation of the benzylisoquinoline ring to the tetrahydroisoquinoline ring provided an even further increase in potency of the molecules without detrimental effects to other pharmacological properties: this key finding led to the rapid adoption of the tetrahydroisoquinolinium structures as a standard building block (along with a 1-benzyl attachment), and it is the primary reason why the continued unwarranted reference to "benzylisoquinolinium" is a complete misnomer for all clinically introduced and currently used neuromuscular blocking agents in this class because they are all, in fact, tetrahydroisoquinoline derivatives. By definition, therefore, there has never been, in the history of clinical anesthetic practice, the use of a benzylisoquinoline neuromuscular blocking agent. The heritage of mivacurium and indeed its very closely related cousin, doxacurium chloride, harks back to the synthesis of numerous compounds following structure-activity relationships that drove researchers to find the ideal replacement for succinylcholine (suxamethonium). Both mivacurium and doxacurium are descendants of early vigorous attempts to synthesize potent non-depolarizing agents with pharmacophores derived from cross-combinations of the non-depolarizing agent, laudexium, and the well-known depolarizing agent, succinylcholine (suxamethonium chloride). Ironically, laudexium itself was invented by a cross-combination between the prototypical non-depolarizing agent, d-tubocurarine and the depolarizing agent, decamethonium. From the 1950s through to the 1970s, the present-day concept of a neuromuscular blocking agent with a rapid onset and an ultra-short duration of action had not taken root: researchers and clinicians were still on the quest for potent but non-depolarizing replacements devoid of the histamine release and the dreaded "recurarizing" effects seen with tubocurarine and, more importantly, the absence of a depolarizing mechanism of action as seen with succinylcholine and decamethonium. Clinical pharmacology and pharmacokinetics The first clinical trial of mivacurium (BW1090U), in 1984, was conducted in a cohort of 63 US patients undergoing surgical anesthesia. at the Harvard Medical School at Massachusetts General Hospital, Boston, MA. Preliminary data from the study confirmed a promise for this agent to elicit considerably lesser severity of histamine release than that observed with its immediate predecessor