A comparison of the efficacy of HI6 and 2-PAM against soman, tabun, sarin, and VX in the rabbit

This study compared the efficacy of HI6 and 2-PAM against nerve agent (soman, tabun, sarin, and VX) -induced lethality in the atropinesterase-free rabbits pretreated with vehicle (controls) or pyridostigmine. Treatment was administered at signs or 2 min after agent challenge and consisted of oxime (100 μmol/kg) + atropine (13 mg/kg) (alone or together with diazepam). Twenty-four-h LD₅₀, values were calculated for soman- and tabun-intoxicated animals, whereas 24-h survival was noted in animals given 10 LD₅₀s of sarin or VX. In pyridostigmine and control rabbits intoxicated with soman and treated with oxime + atropine (alone or together with diazepam), HI6 was 3–5 times more effective than 2-PAM. In contrast, HI6 was less effective than 2-PAM against tabun poisoning. In pyridostigmine-pretreated animals exposed to tabun, efficacy was increased more than 3-fold when compare to tabun-challenged animals treated with atropine + HI6 alone. Both oximes were highly effective against sarin and VX. These findings suggest that HI6 could replace 2-PAM as therapy for nerve agent poisoning, because it is superior to 2-PAM against soman, and when used in pyridostigmine-pretreated animals, it affords excellent protection against all four nerve agents when used in combination with atropine (alone or together with diazepam) therapy.