Utility of Automated Infrared Pupillometry in Assessing the Prolonged Course of Organophosphate Poisoning: A Case Report

Central and autonomic nervous system signs of organophosphate poisoning (OP), such as altered consciousness, noticeable lacrimation, and salivation, can be influenced by medications used in intensive care settings, such as atropine and pralidoxime methyl (PAM). Because of this, there are no established methods for assessing the duration of OP while receiving antidotal treatment. In the present case, we used the Neurological Pupil Index (NPi) to evaluate the duration of OP in an 82-year-old woman who attempted suicide by ingesting up to 100 mL of fenitrothion. Until hospitalization day (HD) 20, discontinuation of atropine led to the recurrence of altered consciousness, while its reinstatement resulted in improvement; this made it difficult to assess the prolongation of OP based on signs and symptoms. Until HD 20, the NPi remained at 0/0, and subsequently, it increased. Additionally, even after discontinuing atropine, consciousness, tearing, and salivation did not worsen, indicating recovery from OP. On HD 26, serum acetylcholinesterase (AChE) levels were elevated above the measurable level for the first time, following an increase in the NPi. In this case, assessing the persistence of OP based on signs was challenging because these signs improved with atropine and PAM treatment. The improvement in NPi levels coincided with an improvement in poisoning, suggesting that NPi is useful for evaluating the duration of OP. NPi is noninvasive and sensitive compared to AChE, which is used to gauge the persistence of OP and could be used to allow earlier cessation of medication and guide appropriate treatment durations.

Acetylcholinesterase Inhibition in Rats and Humans Following Acute Fenitrothion Exposure Predicted by Physiologically Based Kinetic Modeling-Facilitated Quantitative In Vitro to In Vivo Extrapolation

Worldwide use of organophosphate pesticides as agricultural chemicals aims to maintain a stable food supply, while their toxicity remains a major public health concern. A common mechanism of acute neurotoxicity following organophosphate pesticide exposure is the inhibition of acetylcholinesterase (AChE). To support Next Generation Risk Assessment for public health upon acute neurotoxicity induced by organophosphate pesticides, physiologically based kinetic (PBK) modeling-facilitated quantitative in vitro to in vivo extrapolation (QIVIVE) approach was employed in this study, with fenitrothion (FNT) as an exemplary organophosphate pesticide. Rat and human PBK models were parametrized with data derived from in silico predictions and in vitro incubations. Then, PBK model-based QIVIVE was performed to convert species-specific concentration-dependent AChE inhibition obtained from in vitro blood assays to corresponding in vivo dose-response curves, from which points of departure (PODs) were derived. The obtained values for rats and humans were comparable with reported no-observed-adverse-effect levels (NOAELs). Humans were found to be more susceptible than rats toward erythrocyte AChE inhibition induced by acute FNT exposure due to interspecies differences in toxicokinetics and toxicodynamics. The described approach adequately predicts toxicokinetics and acute toxicity of FNT, providing a proof-of-principle for applying this approach in a 3R-based chemical risk assessment paradigm.

An exploratory study; the gap between real reference interval and currently used reference interval of RBC AChE activities in South Korea

The current reference interval (RI) FOR red blood cell acetylcholinesterase (RBC AChE) activity in South Korea was established with data obtained from populations outside the country. The aim of this study was to assess the transferability of current RI of RBC AChE activity for organophosphate (OP) poisoning and determine the biological characteristics, real RI, and interindividual variation in RBC AChE activity in South Korea. Data were retrospectively collected for RBC AChE activity as measured by the modified Ellman's method for 782 patients who presented to our hospital. The clinical course did not differ significantly with the degree of deviation of RBC AChE activity from the currently used RI in 195 patients exposed to OP. RBC AChE activity was associated with gender and smoking status but not age or body mass index (BMI); however, a regression model incorporating age, gender, smoking status and BMI explained only a small portion of the variance in RBC AChE activity in South Korea. The RI of RBC AChE activity was 9,403-16,825 U/L, with 13.9% interindividual variation. The range of RBC AChE activity in South Korea is wider than RI currently used in clinical practice and exhibited a high degree of interindividual variation. In the absence of collecting pre-exposure values, it is recommended to conduct serial measurements, rather than one-point measurements, of RBC AChE activity as evidenced by the RI in OP poisoning.

Potential clinical application of surface electromyography as indicator of neuromuscular recovery during weaning tests after organophosphate poisoning

This study aimed to explore the usefulness of measuring respiratory muscle activity in mechanically ventilated patients suffering from acute organophosphate poisoning, with a view towards providing complementary information to determine the best time to suspend ventilatory support. Surface electromyography in respiratory muscles (diaphragm, external intercostal and sternocleidomastoid muscles) was recorded in a young man affected by self-poisoning with an unknown amount of parathion to determine the muscle activity level during several weaning attempts from mechanical ventilation. The energy distribution of each surface electromyography signal frequency, the synchronization between machine and patient and between muscles, acetylcholinesterase enzyme activity, and work of breathing and rapid shallow breathing indices were calculated in each weaning attempt. The work of breathing and rapid shallow breathing indices were not correlated with the failure/success of the weaning attempt. The diaphragm gradually increased its engagement with ventilation, achieving a maximal response that correlated with successful weaning and maximal acetylcholinesterase enzyme activity; in contrast, the activity of accessory respiratory muscles showed an opposite trend.