Efficacy of Oral Administration of Sodium Thiosulfate and Glycine in a Large, Swine Model of Oral Cyanide Toxicity

Study objective: Cyanide is a deadly poison, particularly with oral exposure, in which larger doses can occur before any symptoms develop. Multiple governmental agencies highlight oral cyanide as an agent that can be used in a terrorist attack because it can be easily weaponized and is readily available. Currently, there are no Food and Drug Administration–approved antidotes specifically for oral cyanide. An oral countermeasure that can neutralize and prevent absorption of cyanide from the gastrointestinal tract after oral exposure is needed. The objective of this study is to determine if the combination of glycine and sodium thiosulfate administered orally is effective in reducing mortality in a large, swine model of oral cyanide toxicity. Methods: Nine swine (45 to 55 kg) were instrumented, sedated, and stabilized. Potassium cyanide (at 8 mg/kg) in saline solution was delivered as a onetime bolus through an orogastric tube. Three minutes after cyanide administration, animals that were randomized to the treatment group received sodium thiosulfate (508.2 mg/kg, 3.25-M solution) and glycine (30 mg/kg, 3.5-M solution) through an orogastric tube. Survival at 60 minutes was the primary outcome. We compared survival between groups by log-rank Mantel-Cox analysis and trended laboratory results and vital signs. Results: At baseline and treatment, all animals were similar. Survival at 60 minutes was 100% in treated animals compared with 0% in the control group (P=.003). By the study end, defined as death or 60 minutes after cyanide administration, there was a significant difference in the lactate concentration between the treatment and control groups (control 9.43 mmol/L [SD 4.08]; treatment 1.66 mmol/L [SD 0.82]; difference between means 7.69 mmol/L [SD 2.07]; 95% confidence interval difference –14.05 to –1.32). Mean arterial pressure was significantly different between the treatment and control groups at study end (control 26 mm Hg [SD 6.7]; treatment 81 mm Hg [SD 14]; difference between means 55.2 mm Hg [SD 7.1]; 95% confidence interval difference 37.8 to 72.6). pH and oxygen saturation were also significantly different between the treatment and control groups at study end. Conclusion: The combination of oral sodium thiosulfate and glycine significantly improved survival and physiologic parameters in a large-animal model of oral cyanide toxicity.