Efficacy of the oxime HI-6 dimethanesulphonate in the treatment of guinea-pigs exposed to the nerve agents GB and GD.

The bispyridinium oxime HI-6 DMS is in development as an improved therapy for the treatment of patients exposed to organophosphorus nerve agents. The aim of the work described in this paper was to provide non-clinical data to support regulatory approval of HI-6 DMS, by demonstrating efficacy against an oxime-sensitive agent, GB and an oxime-resistant agent, GD. We investigated the dose-dependent protection afforded by therapy including atropine, avizafone and HI-6 DMS in guinea-pigs challenged with GB or GD. We also compared the efficacy of 30 mg.kg of HI-6 DMS to an equimolar dose of the current in-service oxime P2S and the dichloride salt of HI-6 (HI-6 Cl). In the treatment of GB or GD poisoning there was no significant difference between the salt forms. The most effective dose of HI-6 DMS in preventing lethality following challenge with GB was 100 mg.kg; though protection ratios of at least 25 were obtained at 10 mg.kg. Protection against GD was lower, and there was no significant increase in effectiveness of HI-6 DMS doses of 30 or 100 mg.kg. For GD, the outcome was improved by the addition of pyridostigmine pre-treatment. These data demonstrate the benefits of HI-6 DMS as a component of nerve agent therapy. © Crown copyright (2023), Dstl.