Behavioral toxicity of anticholinesterases in primates: chronic pyridostigmine and soman interactions

Dose rates for continuous infusion of pyridostigmine bromide required to inhibit 30% and 60% of normal serum cholinesterase activity in rhesus monkeys were determined. The effects of continuous pyridostigmine infusion at these dose-rates on the behavioral toxicity of 5 daily repeated low-dose exposures to a toxic organophosphate (soman) were determined not be deleterious; in fact, they were slightly (and variably) protective. Relative to controls (5-day soman ED50 = 0.89 micrograms/kg/day), pyridostigmine infusions producing 30% and 60% inhibition produced 5-day ED50s of 1.25 and 1.11 micrograms/kg/day, respectively. Variability in response to the pyridostigmine-soman combinations appeared to be greater than in response to daily soman exposure without pyridostigmine infusion.