Nerve agents relative potency

Relative potency of nerve agents can also be expressed in terms of the in vivo dose necessary to produce the same level of cholinesterase inhibition by a specific exposure route. As would be expected, the effectiveness of the agents in inhibiting cholinesterase is closely correlated with their acute toxicity (see Appendix A). 

In keeping with the concept of the RIP discussed under Relative Inhibitory Potency , above, inhibition of lymphocyte and/or platelet NTE and possibly erythrocyte LysoPC hydrolase should be used in conjunction with inhibition of erythrocyte AChE and plasma butyryl-cholinesterase (BChE) to assess the likelihood that an exposure to OP compounds would produce cholinergic and/ or delayed neuropathic effects. Erythrocyte AChE inhibition has long been used as a biomarker of exposure to conventional nerve agents or OP insecticides (Lotti, 1995 Wilson and Henderson, 1992). BChE can be sensitive to both conventional and DN agents, and its inhibition could thus serve as a general biomarker for OP agents (Kropp and Richardson, 2007 Van der Schans et al, 2008). 

Generally, the ability of currently available oximes including H oximes to reactivate tabun-inhibited AChE in peripheral as well as central compartment is relatively low. On the contrary of other nerve agents, obidoxime has a higher potency to reactivate tabun-inhibited AChE than HI-6 especially in the central compartment (25). 

From a military perspective, it is not necessarily the lethality of a percutaneous threat agent that is of primary concern but its ability to cause incapacitation. On this basis, HD can be considered to be equipotent to VX (the most toxic of nerve agents). In addition, the pathological consequences of HD exposure would likely impose a substantial burden on medical resources. Thus, while HD is not generally considered to be a lethal agent, its vesicant potency combined with its relative persistence and delayed effects contribute to its reputation as king of the war gasses . 

A.P. Watson, T.D. Jones, J.D. Adams. Relative Potency Estimates of Acceptable Residues and Reentry Intervals After Nerve Agent Release. ... 

Many substances of widely different chemical structure abolish the excitability of nerve fibers on local application in concentrations that do not cause permanent injury and that may not affect other tissues. Sensory nerve fibers are most susceptible, so that these agents produce a selective sensory paralysis, which is utilized especially to suppress the pain of surgical operation. This property was first discovered in cocaine, but because of its toxicity and addiction liability, it has been largely displaced by synthetic chemicals. The oldest of these, procaine (novocaine), is still the most widely used. Its relatively low toxicity renders it especially useful for injections, but it is not readily absorbed from intact mucous membranes and is therefore not very effective for them. Many of its chemical derivatives are also used. They differ in penetration, toxicity, irritation, and local injury as well as in duration of action and potency. Absolute potency is not so important for practical use as is its balance with the other qualities. If cocaine is absorbed in sufficient quantity, it produces complex systemic actions, involving stimulation and paralysis of various parts of the CNS. These are mainly of toxicological and scientific interest. Its continued use leads to the formation of a habit, resembling morphinism. This is not the case with the other local anesthetics. 

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