PHOSPHATE ESTER POISONING, A NEW PROBLEM FOR THE INTERNIST

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Abstract
During the past 3 yrs. several agricultural insecticides of the phosphate ester type have grown rapidly in usage and economic importance. Their efficacy is due to their high toxicity for a wide range of insects, but these compounds, unfortunately, are highly toxic for man and other animal life as well. They can be applied safely if stringent precautions are rigidly adhered to. These compounds owe their pharmacol-ogic activity to marked cholinesterase [ChE]-inhibiting effects. Through the inactivation of ChE acetylcholine accumulation results, giving rise to a clinical picture of muscarine-, and nicotine-like effects. Signs and symptoms of poisoning do not usually appear until plasma and erythrocyte levels of ChE have been depressed to 30% or less of normal. Physicians may, therefore, be confronted with an acute emergency in which death may rapidly supervene, unless prompt treatment is instituted. Atropine, pushed to therapeutic limits, may be life-saving. Such poisoning is essentially an acute episode, usually of 24-48 hrs. duration, which results in no residual changes except for a gradually decreasing depression of ChE levels. Diagnosis can be confirmed, and the clinical course evaluated by, quantitative detns. of the ChE levels of plasma and erythrocytes. A modification of the Michel method is well-suited to such detns. Patients recovering from such acute poisoning should not undergo further exposure to phosphate esters or other ChE inhibitors until the return to virtually normal levels of ChE in plasma and erythrocytes has been demonstrated.