[The kinetics of plasma catecholamine in alkylphosphate poisoning and their therapy]

Medical management of incidents with chemical warfare agents

Successful management of incidents with chemical warfare agents strongly depends on the speed of medical help and the ability of helpers to react properly. Though the general principles of clinical toxicology, such as decontamination, stabilization, patient evaluation and symptomatic treatment are similar for many toxicants, chemical warfare agents deserve special attention because of their very high inhalative and cutaneous toxicity, rapid onset of the disease and multiple organ failures. This article describes the medical management of mass casualties with blister agents, nerve agents and blood agents from the viewpoint of a clinical toxicologist. Characteristic diagnostic signs, decontamination procedures and therapeutic schemes for these agents are described. Treatment options are discussed. The importance of planning (e.g. antidote availability) and preparedness is emphasized.

The role of oximes in the management of organophosphorus pesticide poisoning

The number of intoxications with organophosphorus pesticides (OPs) is estimated at some 3,000,000 per year, and the number of deaths and casualties some 300,000 per year. OPs act primarily by inhibiting acetylcholinesterase (AChE), thereby allowing acetylcholine to accumulate at cholinergic synapses, disturbing transmission at parasympathetic nerve endings, sympathetic ganglia, neuromuscular endplates and certain CNS regions. Atropine is the mainstay of treatment of effects mediated by muscarine sensitive receptors; however, atropine is ineffective at the nicotine sensitive synapses. At both receptor types, reactivation of inhibited AChE may improve the clinical picture. The value of oximes, however, is still a matter of controversy. Enthusiastic reports of outstanding antidotal effectiveness, substantiated by laboratory findings of reactivated AChE and improved neuromuscular transmission, contrast with many reports of disappointing results. In vitro studies with human erythrocyte AChE, which is derived from the same single gene as synaptic AChE, revealed marked differences in the potency and efficacy of pralidoxime, obidoxime, HI 6 and HLö 7, the latter two oximes being considered particularly effective in nerve agent poisoning. Moreover, remarkable species differences in the susceptibility to oximes were revealed, requiring caution when animal data are extrapolated to humans. These studies impressively demonstrated that any generalisation regarding an effective oxime concentration is inappropriate. Hence, the 4 mg/L concept should be dismissed. To antagonise the toxic effects of the most frequently used OPs, pralidoxime plasma concentrations of around 80 mumol/L (13.8 mg/L pralidoxime chloride) should be attained while obidoxime plasma concentrations of 10 mumol/L (3.6 mg/L obidoxime chloride) may be sufficient. These concentrations should be maintained as long as circulating poison is expected to be present, which may require oxime therapy for up to 10 days. Various dosage regimens exist to reach this goal. The most appropriate consists of a bolus short infusion followed by a maintenance dosage. For pralidoxime chloride, a 1 g bolus over 30 minutes followed by an infusion of 0.5 g/h appears appropriate to maintain the target concentrtion of about 13 mg/L (70 kg person). For obidoxime chloride, the appropriate dosage is a 0.25 g bolus followed by an infusion of 0.75 g/24 h. These concentrations are well tolerated and keep a good portion of AChE in the active state, thereby retarding the AChE aging rate. AChE aging is particularly rapid with dimethyl phosphoryl compounds and may thwart the effective reactivation by oximes, particularly in suicidal poisoning with excessive doses. In contrast, patients with diethyl OP poisoning may particularly benefit from oxime therapy, even if no improvement is seen during the first days when the poison load is high. The low propensity to aging with diethyl OP poisoning may allow reactivation after several days, when the poison concentration drops. Rigorous testing of the benefits of oximes is only possible in randomised controlled trials with clear stratification according to the class of pesticides involved, time elapsed between exposure and treatment and severity of cholinergic symptoms on admission.

Paraoxon sensitive phenylvalerate hydrolase in assessing the severity of acute paraoxon poisoning

INTRODUCTION

Intoxications with organophosphorous compounds, especially paraoxon, are frequent. Organophosphorous compounds inhibit serine hydrolases such as acetylcholine, butyrilcholine, and carboxyl esterases although acetylcholine and butyrylcholine are too sensitive to paraoxon to be useful markers of severity. They cannot show a dose-dependent inhibition during an acute organophosphorous compounds exposure because maximal enzyme inhibition is reached at very low organophosphorous compounds concentrations.

PURPOSE

To determine in vitro the dose-effect relationship between the activity of the paraoxon-sensitive phenylvalerate hydrolase, a member of the carboxvl esterases family, and the paraoxon dose, and to assess its utility as a putatively less sensitive enzyme marker to monitor the severity of an acute paraoxon intoxication.

MATERIALS AND METHODS

Phenylvalerate hydrolase and butyrylcholine activities were determined in serum of nine healthy human volunteers before and after addition of different concentrations of paraoxon. The determination of phenyl-valerate hydrolase activity was carried out using a modification of the method described by Johnson. A commercially available kit was used to measure butyrylcholine activity.

RESULTS

Paraoxon inhibits phenyl-valerate hydrolase activity at concentrations above 10 M. Maximal inhibition (approximately 50% of baseline) is achieved at concentrations above 2.5 x 10(-7) M. The IC50 value of paraoxon for phenyl-valerate hydrolase is 34+/-2 nM. The uninhibited phenyl-valerate hydrolase activity is due to paraoxon-resistent isoforms. Paraoxon begins inhibiting butyrylcholine activity at concentrations above 10(-9) M. At concentrations above 5 x 10(-5) M, no butyrylcholine activity is measulrable. The IC50 value of paraoxon for butyrylcholine is 150+/-23 nM.

CONCLUSION

The paraoxon-sensitive subunit of phenyl-valerate hydrolase shows dose-dependent inhibition when exposed to paraoxon in vitro, but it is even more sensitive than butyrylcholine to paraoxon inhibition. Determinations of phenyl-valerate hydrolase activity to assess the severity of an acute organophosphorous compounds poisoning cannot be recommended, but phenyl-valerate hydrolase may have utility in worker surveillance.

L-lactate reduces in vitro the inhibition of butyrylcholinesterase (BChE) by paraoxon (E 600)

Intoxication with the organophosphorus compound paraoxon (POX), an inhibitor of serine hydrolases, is frequent. Oximes are the only enzyme reactivators clinically available. Serendipitous observation led us to the hypothesis that lactate might attenuate some of the POX effects. In vitro effects of lactate on the inhibition of butyrylcholinesterase (BChE) by POX were assessed in plasma of 12 healthy human volunteers. The determinations were repeated using different lactate and different POX concentrations. The BChE activity determinations were performed in the following settings: (i) baseline untreated plasma (BL); (ii) after addition of POX to plasma (pl+POX); (iii) after POX and plasma were incubated and then lactate was added (pl+POX/lact); (iv) after addition of lactate to plasma (pl+lact); (v) after lactate and plasma were incubated and then POX was added (pl+lact/POX); (vi) after lactate and POX were incubated and then added to plasma (lact+POX/pl). In the micro- and millimolar ranges, lactate is able to abolish in vitro the inhibition of BChE by POX in human plasma when added to plasma prior to POX or when incubated with POX prior to addition to plasma. Lactate added to plasma after POX has no protective effect. In a second set of experiments, the effect of lactate on BChE activity was determined. At high millimolar concentrations, lactate itself inhibits BChE to an extent comparable to POX. Lactate is a mixed inhibitor of BChE, being able to interfere with the enzyme-substrate complex (inhibition constant for the enzyme-inhibitor-substrate complex K'I(EIS) = 81 mM) and the enzyme (inhibition constant for the enzyme-inhibitor complex K(I) (EI) = 26 mM).

[Plasma and urine catecholamines in a 7-day survival of parathion poisoning]

During the intensive medical treatment of a finally fatal parathion poisoning (survival time 7 days) with shock symptoms (lung and kidney) the kinetic profiles of both plasma and urinary catecholamines were taken up. In addition the parathion concentrations of the same plasma samples were measured. There could have been found plasma catecholamine profiles exhibiting peak concentrations in the initial phase, followed by a period of 4 days without any detectable plasma epinephrine and finally an extreme elevation of both catecholamines in the last period before death. The excretion patterns confirmed the plasma results. Imaginable pathophysiological mechanisms in consideration of the shock induced renal insufficiency are discussed. The question is raised whether the kinetics of plasma catecholamines may be a possible marker for the prognosis of organophosphate poisoning.