Some benefit from non-oximes MB408, MB442 and MB444 in combination with the oximes HI-6 or obidoxime and atropine in antidoting sarin or cyclosarin poisoned mice

•MB408, MB442 and MB444 are non-oxime bispyridinium experimental compounds.•MB compounds were investigated as adjuncts to therapy of nerve agent poisoning.•MB444 is significantly beneficial for treating cyclosarin poisoning in mice.•Higher dose of each MB compound usually brings slightly higher benefit. The effect of three newly developed bispyridinium non-oxime compounds (MB408, MB442, and MB444) on the therapeutic efficacy of a standard antidotal treatment (atropine in combination with the oxime HI-6 or obidoxime) of acute poisoning by two nerve agents (sarin and cyclosarin) in mice was studied. The therapeutic efficacy of atropine in combination with an oxime with or without one of the bispyridinium non-oximes was evaluated by determination of the 24 h LD50 values of the nerve agents studied and by measurement of the survival time after supralethal poisoning. Addition of all tested non-oximes increased the therapeutic efficacy of atropine in combination with an oxime against sarin poisoning; however, the differences were not significant. The non-oximes also positively influenced the number of surviving mice 6 h after supralethal poisoning with sarin. In the case of cyclosarin, they were also slightly beneficial in the treatment of acute poisoning. The higher dose of MB444 was able to significantly increase the therapeutic efficacy of standard antidotal treatment of poisoning with cyclosarin. The benefit of each bispyridinium non-oxime compound itself was obviously dose-dependent. In summary, the addition of MB compounds to the standard antidotal treatment of acute nerve agent poisoning was beneficial for the antidotal treatment of sarin or cyclosarin poisoning, although their benefit at 24 h after poisoning was not significant, with the exception of the higher dose of MB444 against cyclosarin.