A series of prodrugs of 3-mercaptopyruvate (3-MP), the substrate for the enzyme 3-mercaptopyruvate/cyanide sulfurtransferase (3-MPST) that converts cyanide to the nontoxic thiocyanate, which are highly effective cyanide antidotes, have been developed. These prodrugs of 3-MP are unique in being not only orally bioavailable, but may be administered up to an hour prior to cyanide as a prophylactic agent and are both rapid-or slow-acting when given parenterally.

Historically, antidotal potencies of cyanide antagonists were measured as increases in the experimental LD 50 for cyanide elicited by the antidotes. This required the use of high doses of cyanide following pretreatment with the putative antidote. Since IACUC guidelines at our institutions strongly discourage LD 50 determinations: we developed a new test paradigm that allowed for maximal survival of cyanide-treated animals with greatly reduced numbers of animals. Symptoms of cyanide toxicity include disruption of neuromuscular coordination, i.e., the righting reflex. Therefore, to establish a dose-response curve, the times required for recovery of this righting reflex with increasing doses of cyanide were measured. A cyanide dose that disrupted this righting reflex for approximately one h with minimal deaths was then selected. Using this paradigm, the current cyanide antidotes, viz., nitrite plus thiosulfate and hydroxocobalamin, as well as some potential cyanide antidotes that we developed, were evaluated pre-and post-cyanide. This allowed, for the first time, the assessment of the post-cyanide effectiveness of the current antidotes against cyanide poisoning in a live animal. In addition, some prototype compounds were found to exhibit antidotal efficacy not only when injected i.p. following cyanide, but also when administered orally 30 min before cyanide. Pre-cyanide oral efficacy suggests that such compounds have the potential of being administered prophylactically before exposure to cyanide. This new test paradigm was found to be a powerful tool for assessing the efficacies of some novel antidotes against cyanide and should be equally applicable for evaluating putative antidotes for other neurotoxins.

Current cyanide antidotes are administered by IV infusion which is suboptimal for mass casualties. Therefore, in a cyanide disaster intramuscular (IM) injectable antidotes would be more appropriate. We report the discovery of the highly water-soluble sulfanegen triethanolamine as a promising lead for development as an IM injectable cyanide antidote.