The ability of three oximes (HI-6, trimedoxime, K203) to reduce cyclosarin-induced acute neurotoxic signs and symptoms was compared with the neuroprotective efficacy of two combinations of oximes (HI-6 + trimedoxime, HI-6 + K203) using a functional observational battery. Cyclosarin-induced neurotoxicity and the neuroprotective effects of HI-6, trimedoxime or K203 alone and HI-6 combined with trimedoxime or K203 in rats poisoned with cyclosarin at a sublethal dose (80 μg/kg i.m.; 70% of LD₅₀ value) were monitored by the functional observational battery at 24 hours and 7 days following cyclosarin challenge. The results indicate that all types of antidotal treatment are able to survive cyclosarin-poisoned rats 7 days following cyclosarin poisoning while one non-treated cyclosarin-poisoned rats died within 24 hours following cyclosarin challenge. All three oximes alone as well as both oxime mixtures combined with atropine were able to slightly decrease cyclosarin-induced neurotoxicity in the case of sublethal poisoning but they did not eliminate all cyclosarin-induced acute neurotoxic signs and symptoms. Their ability to reduce cyclosarin-induced acute neurotoxicity was almost the same regardless of type of antidotal treatment. Thus, the tested combinations of oximes were not able to increase the neuroprotective effectiveness of antidotal treatment of acute cyclosarin poisoning compared to the individual oximes.

Keywords: cyclosarin; functional observational battery; neurotoxicity; mixture of oximes; rats