The currently fielded pre-hospital therapeutic regimen for the treatment of organophosphorus (OP) poisoning in the United States (U.S.) is the administration of atropine in combination with an oxime antidote (2-PAM Cl) to reactivate inhibited acetylcholinesterase (AChE). Depending on clinical symptoms, an anticonvulsant, e.g., diazepam, may also be administered. Unfortunately, 2-PAM Cl does not offer sufficient protection across the range of OP threat agents, and there is some question as to whether it is the most effective oxime compound available. The objective of the present study is to identify an oxime antidote, under standardized and comparable conditions, that offers protection at the FDA approved human equivalent dose (HED) of 2-PAM Cl against tabun (GA), sarin (GB), soman (GD), cyclosarin (GF), and VX, and the pesticides paraoxon, chlorpyrifos oxon, and phorate oxon. Male Hartley guinea pigs were subcutaneously challenged with a lethal level of OP and treated at approximately 1 min post challenge with atropine followed by equimolar oxime therapy (2-PAM Cl, HI-6 DMS, obidoxime Cl2, TMB-4, MMB4-DMS, HLö-7 DMS, MINA, and RS194B) or therapeutic-index (TI) level therapy (HI-6 DMS, MMB4-DMS, MINA, and RS194B). Clinical signs of toxicity were observed for 24 hours post challenge and blood cholinesterase [AChE and butyrylcholinesterase (BChE)] activity was analyzed utilizing a modified Ellman’s method. When the oxime is standardized against the HED of 2-PAM Cl for guinea pigs, the evidence from clinical observations, lethality, quality of life (QOL) scores, and cholinesterase reactivation rates across all OPs indicated that MMB4 DMS and HLö-7 DMS were the two most consistently efficacious oximes.

Diisopropylfluorophosphate (DFP) is a potent acetylcholinesterase inhibitor commonly used in toxicological studies as an organophosphorus nerve agent surrogate. However, LD50 values for DFP in the same species can differ widely even within the same laboratory, possibly due to the use of degraded DFP. The objectives here were to identify an efficient synthesis route for high purity DFP and assess the storage stability of both the in-house synthesized and commercial source of DFP at the manufacturer-recommended storage temperature of 4°C, as well as −10°C and −80°C. After 393 days, the commercial DFP stored at 4°C experienced significant degradation, while only minor degradation was observed at −10°C and none was observed at −80°C. DFP prepared using the newly identified synthesis route was significantly more stable, exhibiting only minor degradation at 4°C and none at −10°C or −80°C. The major degradation product was the monoacid derivative diisopropylphosphate, formed via hydrolysis of DFP. It was also found that storing DFP in glass containers may accelerate the degradation process by generating water in situ as hydrolytically generated hydrofluoric acid attacks the silica in the glass. Based on the results here, it is recommended that DFP be stored at or below −10°C, preferably in air-tight, nonglass containers.

A gas chromatography-mass spectrometry method for determining exposure to the chemical warfare agent 2,2'-dichlorodiethyl sulfide (sulfur mustard; HD) has been developed. The technique is based upon quantitating thiodiglycol (TDG) released from blood protein adducts that are formed upon exposure to HD. Protein was precipitated from plasma, whole blood, or packed red blood cells (RBCs) and then treated with sodium hydroxide to liberate protein-bound TDG. The TDG was derivatized with pentafluorobenzoyl chloride that enabled sensitive detection by negative-ion chemical ionization. Octadeuterothiodiglycol was used as an internal standard. Exposure of human plasma to HD (25 nM to 400 nM) resulted in a linear relationship (r2 = 0.9995) between HD concentration and released TDG levels with means ranging from 2.0 to 38 pg/mg protein. The coefficients of variation expressed as a percentage for the data points ranged from 2 to 11.5%. The application of this procedure was demonstrated in two HD animal exposure models. African green monkeys (Chlorocebus aethiops) were exposed intravenously to 1 mg/kg HD, and TDG levels in blood samples were analyzed out to 45 days post-exposure. Mean TDG levels were determined to be 220 pg/mg protein on day 1 and declined to 10 pg/mg protein on day 45. Yorkshire cross pigs (Sus scrofa) were cutaneously exposed to neat liquid HD, and TDG levels in plasma were determined out to 21 days following exposure. Mean TDG levels were found to be 60 pg/mg protein on day one and decreased to an average of 4 pg/mg protein on day 21. The data from this study indicate that the assay is sensitive and provide a relatively simple approach to assay TDG cleaved from blood proteins at relatively long time frames (21-45 days) after HD exposure. The utility of the method has been demonstrated in vivo in a non-human primate and pig HD exposure model.