Oral Pretreatment with Galantamine Effectively Mitigates the Acute Toxicity of a Supra-Lethal Dose of Soman in Cynomolgus Monkeys Post-treated with Conventional Antidotes

The present study was designed to evaluate the effectiveness of galantamine administered orally as a pre-treatment to mitigate the acute toxicity of 4.0xLD50 soman in Cynomolgus monkeys post-treated with atropine, 2-PAM, and midazolam. Pharmacokinetic experiments revealed that the oral doses of 1.5 and 3.0 mg/kg galantamine HBr were quickly absorbed and produced plasma concentrations of galantamine that generated approximately 20% to 40% reversible inhibition of blood acetylcholinesterase (AChE) activity. This degree of reversible AChE inhibition has been shown to be safe and sufficient to protect AChE from the irreversible inhibition by nerve agents, and, thereby, suppress the acute toxicity of these agents. Thus, in subsequent experiments, adult male Cynomolgus monkeys were pretreated orally with 1.5 or 3.0 mg/kg galantamine, challenged intramuscularly with 4.0xLD50, and post-treated with intramuscular injections of 0.4 mg/kg atropine, 30 mg/kg 2-PAM, and 0.32 mg/kg midazolam. All animals subjected to these treatments survived the soman. By contrast, none of the animals that were pretreated with saline and only 40% of the animals that were pretreated with pyridostigmine survived the soman challenge when post-treated with the same conventional antidotal therapy as that delivered to the galantamine-pretreated, soman-challenged monkeys. In addition, large numbers of degenerating neurons were visualized in the hippocampi of soman-challenged monkeys that had been pretreated with pyridostigmine or saline, but not in the hippocampi of animals that had been pretreated with galantamine. To our knowledge, this is the first study to demonstrate the effectiveness of clinically relevant oral doses of galantamine to prevent the acute toxicity of supra-lethal doses of soman in non-human primates.