A role for solvents in the toxicity of agricultural organophosphorus pesticides.

Organophosphorus (OP) insecticide self-poisoning is responsible for about one-quarter of global suicides. Treatment focuses on the fact that OP compounds inhibit acetylcholinesterase (AChE); however, AChE-reactivating drugs do not benefit poisoned humans. We therefore studied the role of solvent coformulants in OP toxicity in a novel minipig model of agricultural OP poisoning. Gottingen minipigs were orally poisoned with clinically relevant doses of agricultural emulsifiable concentrate (EC) dimethoate, dimethoate active ingredient (AI) alone, or solvents. Cardiorespiratory physiology and neuromuscular (NMJ) function, blood AChE activity, and arterial lactate concentration were monitored for 12h to assess poisoning severity. Poisoning with agricultural dimethoate EC40, but not saline, caused respiratory arrest within 30 min, severe distributive shock and NMJ dysfunction, that was similar to human poisoning. Mean arterial lactate rose to 15.6 [SD 2.8] mM in poisoned pigs compared to 1.4 [0.4] in controls. Moderate toxicity resulted from poisoning with dimethoate AI alone, or the major solvent cyclohexanone. Combining dimethoate with cyclohexanone reproduced severe poisoning characteristic of agricultural dimethoate EC poisoning. A formulation without cyclohexanone showed less mammalian toxicity. These results indicate that solvents play a crucial role in dimethoate toxicity. Regulatory assessment of pesticide toxicity should include solvents as well as the AIs which currently dominate the assessment. Reformulation of OP insecticides to ensure that the agricultural product has lower mammalian toxicity could result in fewer deaths after suicidal ingestion and rapidly reduce global suicide rates.

Quantification of pralidoxime (2-PAM) in urine by ion pair chromatography-diode array detection: application to in vivo samples from minipig.

Pralidoxime (2-PAM) is a monopyridinium oxime used as an antidote for the treatment of poisoning with organophosphorus (OP) compounds, for example, pesticides and nerve agents, reactivating OP-inhibited acetylcholinesterase. However, appropriate dosing and efficacy remains a matter of discussion requiring experimental data. Therefore, we developed and validated an ion pair chromatography-diode array detection (IPC-DAD) method suitable for quantitative analysis of 2-PAM in human and porcine urine. Before injection of 20 µl, urine was acidified with trichloroacetic acid, mixed with internal standard (pyridine-4-aldoxime, 4-PAO), and diluted with IPC solvent yielding a total dilution of 1:49.5 and a 100% recovery. Isocratic separation was carried out at 25 °C on a LiChrospher 60 RP-select B column (125 x 4.0 mm I.D.) using phosphate buffer (7.5 mM Na(2) HPO(4) , 7.5 mM KH(2) PO(4) , pH 2.6) mixed with octanesulfonate (2.5 mM) as ion pair reagent and acetonitrile (6% v/v) as organic modifier (1 ml/min). 2-PAM was detected at 293 nm and 4-PAO at 275 nm. The method is rugged, selective, and characterized by good intra-day and inter-day precision (RSD, 1.3-6.0%) and accuracy (88-100%) with a limit of detection at 4.9 µg/ml, a limit of quantification at 9.8 µg/ml, and a broad calibration range from 4.9-2500 µg/ml. The procedure was applied to urine samples obtained from dimethoate poisoned minipigs receiving 2-PAM therapy (intravenous bolus injection and infusion). Results indicate that 60-80% of infused 2-PAM is rapidly (within 1-2 h) excreted in the urine.

The post-tetanic count during vecuronium-induced neuromuscular blockade in halothane-anaesthetized dogs.

OBJECTIVE: To evaluate the post-tetanic count (PTC) for predicting the return of reversible neuromuscular blockade at the n. facialis-m. nasolabialis (nF-mNL) and n. ulnaris-mm. carpi flexorii (nU-mCF) nerve-muscle units (NMUs) during profound vecuronium neuromuscular blockade in halothane-anaesthetized dogs. STUDY DESIGN: Randomized, prospective, experimental study. ANIMALS: Twenty-five dogs (seven male 18 female) undergoing surgery; mean age: 4.8 years; mean body weight 22 kg. METHODS: Thirty minutes after acepromazine (0.05 mg kg(-1)) and morphine (0.5 mg kg(-1)) pre-medication, anaesthesia was induced with intravenous (IV) thiopental and maintained with halothane, N(2)O and O(2). The lungs were mechanically ventilated and end-tidal halothane concentration (Fe'(HAL)) maintained at 1.04%. Neuromuscular transmission was monitored using the train-of-four count (TOFC) at one nF-mNL and both nU-mCF units. Vecuronium (50 microg kg(-1) IV) was injected after 15 minutes constant Fe'(HAL). When the first twitch (T1) at both nU-mCF units had disappeared (t = 0) one (randomly allocated) ulnar nerve was stimulated every 5 minutes using PTC; TOF stimulation continued at the other sites. The PTC was plotted against the interval between recording time and T1's reappearance at the other NMUs. RESULTS: At t = 0, the mean PTC in the contralateral nU-mCF unit was 18 (range 0-20). Mean PTC was a minimum at t = 5, rising to the maximum (20) at 25 minutes. Six dogs were vecuronium-resistant as monitored by PTC. Excluding data from these revealed a strong negative relationship between ulnar PTC and the time taken for T1's return at the facial (r = -0.7018; p < 0.00001) and contralateral ulnar (r = -0.8409; p < 0.00001) NMUs. CONCLUSION AND CLINICAL RELEVANCE: Post-tetanic count monitoring beginning >5 minutes after the TOFC at nU-mCF = 0 provided a reliable estimate of T1's return at ulnar and facial NMUs.