William A. Groff

The effects of blood flow and detoxification on in vivo cholinesterase inhibition by soman in rats

The in vivo time course of cholinesterase inhibition was measured in brain, lung, spleen, hind limb skeletal muscle, diaphragm, intestine, kidney, heart, liver, and plasma of rats receiving 90 micrograms/kg soman, im. This dose of soman produced severe respiratory depression and transient hypertension, but no significant changes in the cardiac output or heart rate of anesthetized rats. The rate and maximal extent of in vivo cholinesterase inhibition by soman varied widely among the tissues. Although cardiac output was unchanged by soman administration, the blood flow in heart, brain, and lung (bronchial arterial flow and arteriovenous shunts) was increased, whereas blood flow in spleen, kidney, and skeletal muscle was decreased. The relative importance of tissue blood flow, tissue levels of cholinesterase and acetylcholinesterase, and tissue levels of soman-detoxifying enzymes (diisopropyl-fluorophosphatase and carboxylesterase) in determining the in vivo rate and maximal extent of cholinesterase inhibition was examined by multiple regression analysis. The best multiple regression model for the maximal extent of cholinesterase inhibition could explain only 63% of the observed variation. The best multiple regression model for the in vivo rate of cholinesterase inhibition contained three independent variables (blood flow, carboxylesterase, and cholinesterase) and could account for 94% of the observed variation. Of these three variables blood flow was the most important, accounting for 79% of the variation in the in vivo rate of cholinesterase inhibition. This suggests that it may be possible to use a flow-limited physiological pharmacokinetic model to describe the kinetics of in vivo cholinesterase inhibition by soman.

The reactivatibility of cholinesterase inhibited by VX and sarin in man.

Abstract The cholinesterase inhibitors VX[S-(2-diisopropylaminoethyl) O-ethyl methyl phosphonothiolate] and sarin (isopropyl methyl phosphonofluoridate) were given to normal subjects. An iv dose of 1.5 μg/kg and an oral dose of 4.0 μ/kg of VX caused a 75% inhibition of erythrocyte cholinesterase. The oxime 2-pyridinium aldoxime methochloride (2-PAMCI) was administered at varying times and over a range of doses to these subjects who had received VX and also to subjects who had received sarin. It was found that: (a) the RBC-ChE inhibited by VX spontaneously reactivates much faster than that inhibited by sarin, (b) VX-inhibited RBC-ChE ages very little and is amenable to oxime reactivation for as long as 48 hr, and (c) the dose of oxime necessary to reactivate VX-inhibited RBC-ChE is less than that needed to reactivate sarin-inhibited enzyme.

Enhancement of drug absorption after administration by an automatic injector

The effectiveness and rapidity of drug absorption after its administration by an autoinjector was studied in normal male adults. In 12 who received pralidoxime chloride (600 mg) by an autoinjector and by needle and syringe, the plasma concentration of oxime was 82 % higher at 3 min after autoinjector administration, and a therapeutic plasma concentration (4 μg/ml) was attained in about 70% of the time required after needle- and- syringe administration. Atropine given to six subjects by both methods produced tachycardia faster and the time of maximal tachycardia was sooner after autoinjector administration. It is theorized that faster drug absorption occurs because the autoinjector “sprays” the drug through tissue.

Plasma Free Cyanide and Blood Total Cyanide: A Rapid Completely Automated Microdistillation Assay

Techniques are presented which provide direct measurement of both free cyanide (CN-) in plasma and total CN- in whole blood. Loss of total CN- from blood is prevented by conversion to cyanmethemoglobin. Both free and total CN- are assayed by a completely automated method providing readout 17 minutes after sampling. No prior isolation technique is required and sensitivity is adjustable to cover a broad range of CN- concentrations from 1 to 4000 uM. Precision of blood CN- values from 2 to 2500 uM is within +/- 2.3%. No interference results from thiocyanate or thiosulfate at a concentration of approximately 1 mM.

The stability of sarin and soman in dilute aqueous solutions and the catalytic effect of acetate ion

The hydrolysis of aqueous solutions of organophosphonate compounds such as sarin and soman is a critical factor in biochemical and therapeutic studies. The ability to dilute and transport these compounds with assurance of their purity is imperative to the integrity of such studies. An enzymic method has been used to measure low levels of organophosphonates. Maximum stability data were determined in aqueous and isotonic saline solutions. Acetate ion was found to significantly accelerate hydrolysis.1

Passage of pyridinium oximes into human red cells

Abstract Contrary to popular views, pralidoxime chloride, a positively charged oxime and a drug used to treat poisoning from organophosphorus insecticides, penetrates the red cell membrane. Two other therapeutically related drugs that have similar dissociation constants and chemical function groupings penetrate to negligible extents. Pralidoxime chloride did not bind to either red cell stroma or hemoglobin. The rate of entry into red cells by pralidoxime chloride did not change when the pH of blood was changed by ± 0.6 pH unit. Since the rate of entry of pralidoxime chloride into red cells from plasma was identical to the rate at which oxime passed from red cells into plasma, the process was likely due to simple diffusion. In addition, the fraction of pralidoxime chloride entering the red cells was independent of drug concentration. The penetration was not affected by active transport inhibitors, such as ouabain or N -methyl maleimide. The selective penetration could not be related to lipid solubility.

The Reversal of Anticholinergic Intoxication in Man with the Cholinesterase Inhibitor VX

Summary VX, a potent cholinesterase inhibitor, effectively reversed the central effect (delirium) produced by scopolamine and two synthetic anticholinergic compounds in man when VX was administered iv. The therapeutic effectiveness of VX was not diminished by the previous, simultaneous, or subsequent administration of pralidoxime chloride which restored the red blood cell cholinesterase inhibition produced by VX. However, VX administered orally in a dose that produced equivalent red blood cell cholinesterase depression was ineffective. We wish to thank the nurses and technicians of the Clinical Research Branch for the ward care of the subjects. We also thank J. S. Ketchum for helpful suggestions during the study, S. A. Cucinell for constructive comments on the manuscript, and Marion P. Royston for editorial assistance. Part of this report was presented at the April 1973 meeting of the Federation of American Societies of Experimental Biology, Atlantic City, New Jersey.

A Completely Automated Fluorometric Blood Cyanide Method: A Specific Assay Incorporating Dialysis and Distillation

Discrete blood samples can be assayed at a rate of 20/hr. By means of a double lumen catheter, venous or arterial blood can be monitored continuously.