ABSTRACT
Metrifonate is a phosphonate which rearranges to the phosphate, dichlorvos, a well-known insecticide and a direct inhibitor of acetylcholinesterase (Figure 6.4). The best evidence (Reiner et al., 1975) for activation is that pure metrifonate is not an inhibitor and that all of the inhibition of cholinesterase is due to another compound produced from it. Direct chemical proof was provided when it was shown using gas chromatography and mass fragmentation methods that equitoxic doses to mice of dichlorvos and metrifonate lead to similar concentrations in the blood (Nordgren et al., 1978). As shown in Figure 6.4 the production of dichlorvos from metrifonate is a chemical reaction influenced by the composition of the medium (e.g. pH) but not catalysed by an enzyme (i.e. activated but not bioactivated).
