Inhibition of blood cholinesterases by nerve agents in vitro

The bimolecular rate constants (ka) of inhibition were determined for cholinesterase in rat blood in vivo and three nerve agents in vitro. They were in the range of 105-106 M.min -1 with the highest value for VX (ka = 8.92 × 106), the next highest for soman (ka = 3.22 × 106) and the lowest for sarin (ka = 0.39 × 106), respectively. The inhibition rate is the same in vitro and in vivo; when the real inhibition in vivo and in vitro is compared, it is possible to assess the concentration of the nerve agent present in the blood stream. When administered intramuscularly it is about 70% of the dose administered.