Comparison of serum concentrations of the acetylcholinesterase oxime reactivators HI-6, obidoxime, and PAM to efficacy against sarin (isopropyl methylphosphonofluoridate) poisoning in rats.

A comparison of serum concentrations of the oximes HI-6 [1-(((4-aminocarbonyl)-pyridino)methoxy)methyl)-2(hydroxy imino)methyl- pyridinium dichloride], PAM [2-[hydroxyimino)methyl-1-methylpyridinium chloride], and obidoxime [1,1'-(oxybis(methylene]bis(4-((hydroxyimino) methyl)-pyridinium dichloride] to the efficacy against sarin (350 micrograms/kg; sc) lethality was evaluated in rats. The oximes were administered prophylactically by means of Alzet osmotic minipumps. Atropine (17.4 mg/kg; im) was administered immediately following sarin (350 micrograms/kg; sc) administration. At serum concentrations of 3.6, 3.6, and 3.3 micrograms/ml for HI-6, obidoxime, and PAM, respectively, the 24-hr mortality following sarin poisoning was 0, 90, and 20%. The serum oxime concentrations (ED50 values) for HI-6, obidoxime, and PAM against a 3 LD50 dose of sarin were 0.72, 9.05, and 2.56 micrograms/ml, respectively. HI-6 was determined to be the most efficacious oxime when combined with atropine against sarin poisoning followed in order by PAM and obidoxime.