Treatment of paraquat poisoning in man: methods to prevent absorption

Dose ingested, vomiting, and outcome in patients ingesting a standard paraquat 20SL formulation

BACKGROUND

FAO specifications for liquid paraquat dichloride SL formulations require the use of an emetic agent to stimulate vomiting within 30 min of ingestion. To date, there is no high-quality evidence of efficacy, despite use of the PP796 emetic since 1979. We first examined the validity of patients' self-reported dose of paraquat ingested by examining the relationship with blood paraquat concentration and time to death for patients ingesting the standard paraquat SL formulation in a Sri Lankan cohort. As a secondary outcome, we assessed whether ingestion resulted in vomiting within 30 min and whether vomiting was associated with good outcome.

METHODS

Patients presenting with paraquat SL self-poisoning were prospectively studied in ten Sri Lankan hospitals in 2003-08. Data on reported dose ingested, incidence and timing of vomiting after ingestion, treatment received, plasma paraquat concentration, and outcome were collected prospectively on presentation to hospital. Time between ingestion and blood sampling was incorporated by covariate adjustment.

RESULTS

441 patients were recruited to the case series, presenting a median (IQR) of 3.0 (1.5-8.1] h post ingestion. Outcome was known for 435 patients of whom 322 (74.0%) died within 42 days, a median of 1.3 (0.6-4.4) days post ingestion. Median reported dose ingested was 15 to <30 mL. There was a highly significant linear trend between log plasma paraquat and reported dose ingested (p < .001); adjustment for the log of the time from ingestion to sampling further improved the model fit. Case fatality and median time to death also showed good agreement with estimated ingestion amount. 347/438 patients (79.2%) were stated to have vomited before reaching the study hospital with 300 (68.5%) vomiting within 30 min of ingestion; time to vomiting was unknown for a further 12 (2.7%). The proportion vomiting was strongly associated with reported dose ingested (p < .001); of note the proportion vomiting within 30 min only increased to 83.3% for the highest ingestion group. Patients vomiting within 30 min had higher plasma paraquat concentrations (p = .008), and higher hazard ratio in the adjusted Cox regression model of 2.01 (95% CI 1.45-2.77) compared to those who did not. Vomiting within 30 min was associated with a higher case fatality (241/295 [81.7%] vs 68/125 [54.4%], p < .001). Forty-three (47.3%) of the 91 patients who did not vomit before reaching hospital died (one had unknown outcome).

CONCLUSION

Importantly, we found good agreement between reported dose ingested and plasma paraquat concentration, case fatality, and time to death, suggesting that the reported dose is a valid marker for the dose ingested. Vomiting occurred within 30 min for 68.5% of patients, exceeding the characteristics for a purported effective emetic in the FAO specifications. However, vomiting within 30 min was associated with approximately double the risk of death compared to those who did not vomit, larger paraquat ingestions, and higher blood paraquat concentrations. In addition, death occurred in many patients who did not vomit, and the proportion vomiting within 30 min only reached 82.1% for the highest ingested dose group. Overall, we found no evidence of benefit resulting from incorporation of the emetic, suggesting that the current FAO specification is not effective at preventing deaths after ingestion of the paraquat SL formulation.

Evidence for the efficacy of the emetic PP796 in paraquat SL20 formulations - a narrative review of published and unpublished evidence

BACKGROUND

The bipyridyl herbicide paraquat was first introduced into agriculture in the 1960s by Imperial Chemical Industries. Due to issues with unintentional poisoning, the centrally acting emetic PP796 was added in 1976 to the company's 20% paraquat ion soluble liquid (SL20) formulations (Gramoxone^®) at a concentration of 0.5 g/L or 0.05% (equivalent to 0.071 mg/kg in a 70 kg adult ingesting a minimum lethal dose of 10 mL) to induce early vomiting (within 30 min), reduce paraquat absorption from the gut, and prevent deaths. Its presence in paraquat products was subsequently mandated by the Food and Agriculture Organization Committee of Experts on Pesticides in Agriculture (predecessor to the current FAO/WHO Joint Meeting on Pesticide Specifications). However, no primary pre-clinical or clinical data have been published regarding the effectiveness of PP796. We reviewed the published literature and unpublished company reports for data on the effectiveness of PP796.

METHODS

PubMed and Google were searched for published studies on the emetic using the search terms "paraquat" and ["emetic" or "PP796"]. Company documents reporting pre-clinical and clinical studies were accessed at the website of U.S. Right to Know (https://usrtk.org/pesticides/paraquat-papers/). Primary study reports were sought as well as overviews written by company toxicologists.

RESULTS

Pre-clinical dog and monkey studies indicated that the PP796 EC50 dose for vomiting was around 0.5-2 mg/kg. Further increasing the PP796 concentration speeded up the time to first vomit and reduced the amount of paraquat absorbed (as assessed by the 0-24 h plasma area-under-the-curve) 100-fold compared to a control group receiving no PP796. However, the dose selected for paraquat SL20 formulations by the company (0.5 g/L or 0.05%) was based exclusively on a phase II study in the early 1970s involving five volunteers receiving 3 different doses, with only two individuals actually vomiting, supplemented by data from 37 patients taking 2 mg in clinical trials. A UK-mandated toxicovigilance study in the 1980s identified only 21 patients ingesting paraquat SL20 with PP796 for whom data on time to vomit was available; of these patients, 11 vomited within 30 min (52.4%, 95%CI 31-73.7%). No effect on mortality could be identified from any study of paraquat SL containing 0.05% PP796. A clinical study in Sri Lanka 30 years after the emetic was first introduced, of a revised formulation (Gramoxone^® Inteon) containing a three-fold higher amount of PP796, as well as MgSO4 and an alginate, showed increased rates of early vomiting and modestly reduced mortality for patients ingesting up to 100 mL.

CONCLUSION

Pre-clinical studies showed a clear dose response for PP796 to cause early vomiting, with effective doses in the 0.5-20 mg/kg range. A too low concentration of PP796 was selected for paraquat formulations based on an inadequate phase II study. Currently, evidence that PP796 at 0.05% in paraquat SL20 causes more rapid vomiting after ingestion is weak or unpublished; no evidence of clinical benefit or fewer deaths has been identified. There is no evidence to support the FAO/WHO Joint Meeting on Pesticide Specifications mandate to include PP796 or any other emetic in paraquat products. Products with higher emetic concentrations have been developed but are not widely used; it is possible they may prevent deaths.

Case Report: Delayed Lung Transplantation With Intraoperative ECMO Support for Herbicide Intoxication-Related Irreversible Pulmonary Fibrosis: Strategy and Outcome

Background: Lung transplantation is recognized as the only therapeutic option for patients who develop irreversible pulmonary fibrosis after herbicide intoxication. Methods: We have collected and presented clinical course and outcome of four patients who received lung transplantation due to paraquat and diquat intoxication from 2018 to 2021. Another patient who received initial lung transplantation due to paraquat intoxication and re-transplantation due to chronic lung allograft dysfunction in 2019, was further reported. Patients were admitted in lung transplantation centers, including the 1^st affiliated hospital of Zhengzhou University and Wuxi Lung transplantation center. Previous reported cases from Europe, Canada and China were also summarized as benchmark. Results: During the period from the year of 2018 to 2021, there have been four patients in China, who received lung transplantation due to herbicide intoxication. Median age of the four patients was 37 (IQR 34.5, 39.75) years old. Median time from intoxication to lung transplantation was 27.5 (IQR 27, 30.5) days. Bilateral lung transplantation was performed in three patients, while one single lung transplantation was performed in an urgent listed patient. Extracorporeal Membrane Oxygenation (ECMO) and hemopurification support were used in all patients (100%). Details of the cases with follow-ups were further presented and analyzed. Conclusions: Late timing of bilateral lung transplantation can be performed successfully for pulmonary fibrosis after paraquat or diquat intoxication. The survival of patients with complex perioperative conditions can be achieved with a multidisciplinary team to manage the irreversible effects of intoxication.

Mineralogical and Physico-Chemical Characterization of the Oraşu-Nou (Romania) Bentonite Resources

The objective of this study is to describe the mineralogical composition and chemical properties of the Oraşu Nou bentonite, from northwestern Romania. For mineralogical determinations, the following were used: X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FR-IR), thermogravimetric analysis, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX). The chemical compositions and physical properties of the bentonites and bentonitized rocks were also determined. Calcium type montmorillonite is the predominant mineral in this deposit. Its average mass fraction is between 35% and 75%, reaching up to 95%. A small amount of halloysite and very fine cristobalite were also identified in the fine fraction. Quartz, feldspar, and kaolinite were identified as impurities. The average pH of natural bentonite is 6.2. Its cation exchange capacity (CEC) is in the lower-middle range for smectites at 45.89 cmol/kg, absorption capacity 43.58 mL/g, swelling degree 9.41%. Because of the high amounts and purity of montmorillonite, the valuable component mineral, the way is open to an easy refinement of this important resource. This way very high-quality colloidal suspensions can be obtained which can be used in the most modern applications of micro- and nanostructured materials.

Endoplasmic reticulum stress promotes epithelial‑mesenchymal transition via the PERK signaling pathway in paraquat‑induced pulmonary fibrosis

Pulmonary fibrosis is the primary reason for mortality in patients with paraquat (PQ) poisoning. Our previous study demonstrated that epithelial-mesenchymal transition (EMT) had a role in PQ-induced pulmonary fibrosis. However, the role of endoplasmic reticulum (ER) stress in PQ-induced EMT remains clear. The present study aimed to determine the role of ER stress in EMT in PQ-induced pulmonary fibrosis. A549 and RLE-6TN cells were incubated with LY294002 (a PI3K inhibitor) or transfected with protein kinase RNA-like ER kinase (PERK) small interfering RNA (si) for 24 h prior to being exposed to PQ. Next, the expression levels of ER stress-related proteins, PI3K/AKT/GSK-3β signaling pathway-related proteins and EMT-related markers were analyzed by performing western blotting, reverse transcription-quantitative PCR and immunofluorescence assays. The results of the present study revealed that the protein expression levels of PERK, phosphorylated (p)-PERK, p-eukaryotic initiation factor 2 (eIF2)α were significantly upregulated in the PQ group, whereas p-PI3K, p-AKT and p-GSK-3β were significantly upregulated in the sicontrol + PQ group compared with the sicontrol group. In vitro, following transfection with siPERK or treatment with the PI3K inhibitor, the protein expression levels of E-cadherin (an epithelial marker) were upregulated, whereas the protein expression levels of α-SMA (a mesenchymal marker) were downregulated. Immunofluorescence analysis revealed that the levels of E-cadherin were markedly upregulated, whereas the levels of α-SMA were notably downregulated following transfection with siPERK compared with the sicontrol group. The results of wound healing assay demonstrated that cell migration in the siPERK + PQ group was markedly decreased compared with the sicontrol + PQ group. These indicated that PQ-induced EMT was suppressed after silencing PERK. The expression levels of p-GSK-3β, p-AKT and p-PI3K were also markedly downregulated in the siPERK + PQ group compared with the sicontrol + PQ group. In conclusion, the findings of the present study suggested that ER stress may promote EMT through the PERK signaling pathway in PQ-induced pulmonary fibrosis. Thus, ER stress may represent a potential therapeutic target for PQ-induced pulmonary fibrosis.

User-safe and efficient chitosan-gated porous carbon nanopesticides and nanoherbicides

Nanopesticides are selected as one of ten chemical innovations that will change our world. Carboxylated porous carbon nanoparticles (PCNs) were used to encapsulate water-insoluble pesticides and subsequently capped with chitosan (CS) to prepare the CS-gated PCN (PCN@CS) nanopesticides for the controlled release of pesticides in response to acidic pH and elevated temperature with good fungicidal efficacy. To resolve the issue of gastrointestinal absorption of PQ upon ingestion of PQ formulation, it is an innovative strategy to select the carboxylated PCNs as the paraquat (PQ) nanocarriers to inhibit PQ release in the gastrointestinal tract from the origin. The PQ-loaded PCN@CS nanoherbicides showed very low cytotoxicity to human normal cells and high survival rate in mice because the strong π-π interactions between the electron-deficient PQ and the electron-rich PCNs almost inhibited the release of PQ at both acidic and alkaline pH values. The controlled release of PQ from the nanoherbicides was realized at elevated temperatures owing to the weakening of the strong π-π interactions, aiming to eliminate weeds via the photothermal effect of PCNs under natural sunlight. The user-safe PCN-based PQ formulation can inhibit PQ release in the gastrointestinal tract and keep the PQ herbicidal efficacy in the practical application.

Evaluation of gastric lavage efficiency and utility using a rapid quantitative method in a swine paraquat poisoning model

BACKGROUND

Gastric lavage (GL) is one of the most critical early therapies for acute paraquat (PQ) poisoning; however, details of the treatment protocol remain to be established.

METHODS

A rapid quantitative method involving sodium dithionite testing was developed. It was validated for the determination of the PQ concentrations in gastric juice and eluate samples from a swine acute PQ poisoning model with early or delay GL, or without. The vital signs, laboratory testing, and PQ plasma concentrations were collected for therapeutic effect evaluation.

RESULTS

The reaction conditions of the test were optimized for two types of samples. Early GL at one hour (H1) could improve the signs and symptoms after acute PQ poisoning at 24 hours (H24). In contrast, GL at 6 hours (H6) could only partially relieve the vital signs. The H1 GL group effectively reduced the peak of the plasma PQ concentration. In addition, the PQ concentrations in the plasma and the gastric juice were significantly decreased in both the GL groups as compared to the untreated group at H24. Moreover, there was no significant difference in the washing efficiencies calculated from the total eluates between the two GL groups. However, the washing efficiency of the first 10 L eluate is superior to that of the additional 10 L eluate.

CONCLUSION

GL only at early stage may it benefit PQ poisoning in an animal model. The currently used 20 L GL volume may need to be reduced in view of the low washing efficiency in the later 10 L eluate. The rapid quantitative method can be used for gastric juice sample and has a certain value for clinical GL practices.

Clinical features and prognosis of paraquat poisoning in French Guiana: A review of 62 cases

Paraquat is a nonselective contact herbicide of great toxicological importance, being associated with high mortality rates. Because of its high toxicity, the European Union withdrew it from its market in 2007. The aim of this study is to analyze all cases of paraquat poisoning hospitalized in French Guiana in order to assess their incidence and main characteristics.Medical records of all paraquat intoxicated patients hospitalized from 2008 until 2015 were reviewed in this retrospective study.Demographics, clinical presentation, and laboratory data were evaluated.A total of 62 cases were reviewed. The incidence of paraquat poisoning was 3.8/100,000 inhabitants/year. There were 44 adults and 18 children younger than 16 years of age. The median ages were 31 years [18.08-75.25] in adults and 13.4 years [0.75-15.08] in children, respectively. The median duration of hospitalization was longer in children [15.5 days (1-24)] than in adults [2 days (1-30)], P < .01. The majority of cases was due to self-poisoning (84%).Children had ingested a lower quantity of paraquat [48.8 mg/kg (10-571.1)] than adults [595.8 mg/kg (6-3636.4), P = .03]. There were more deaths among adults (65%) than in children (22%), P = .004. The severity and outcome was determined primarily by the amount of paraquat ingested.In conclusion, French Guiana has the largest cohort of paraquat poisonings in the European Union. The major factor affecting the prognosis of patients was the ingested amount of paraquat. The administration of activated charcoal or Pemba, in situ, within the first hour after ingestion of paraquat is essential.

Efficacy of Whole Bowel Irrigation Using Solutions with or without Adsorbent in the Removal of Paraquat in Dogs

1 The efficacy of whole bowel irrigation with a solution containing either polyethylene glycol (PEG) with electrolyte or an adsorbent (Kayexalate™) with a cathartic (sorbitol) was investigated in 18 dogs who had been given 250 mg kg -1 paraquat dichloride via a jejunal tube to eliminate the influence of gastric absorption.

2 Plasma paraquat concentrations 2 and 3 h after the initiation of bowel irrigation and at the end of the study (5 h later) were significantly lower in the bowel irrigation groups than in the control (no bowel irrigation) group.

3 The total body clearances of paraquat in the bowel irrigation groups were significantly greater than in the control group.

4 There were no significant differences between the two different irrigation solution groups in plasma paraquat concentration, the area under the plasma concentration time curve and the total body clearance.

5 In the PEG with electrolyte group, about 70% of the administered dose of paraquat was removed by means of bowel irrigation (n=4).

6 The adjunction of the adsorbent had no beneficial effects.

7 Haemodynamic changes associated with whole bowel irrigation were unremarkable except that right atrial and pulmonary arterial pressures were elevated in the latter part of the study.

Effect of haemoperfusion on plasma paraquat concentration in vitro and in vivo

This study was to observe the paraquat (PQ) reduction rate after haemoperfusion (HP) on the groups of a relatively large number: 50 survivors out of 105 patients with acute PQ poisoning. We started off by measuring the clearance of haemodialysis (HD) and HP for the PQ in vitro. At the blood flow of 250 mL/min, the PQ clearance was greater in HP than in HD during the first 90 minutes: 215 versus 175 mL/min at 30 minutes, 213 versus 201 mL/min at 60 minutes, and 199 versus 179 mL/min at 90 minutes. The clearance in HP decreased rapidly after two hours. By the end of the dialysis, however, the final concentration in container decreased to 5.7 mg/mL in HD and 1.5 mg/mL in HP, which implied that although HD was cleared more effectively during the later stages, the overall elimination was greater in HP. Following this preliminary investigation, we performed HP on all the patients in order to assess the extracorporeal elimination.

One hundred and five patients who had swallowed one to three mouthfuls of PQ (24.5% w/v) solution were subjected to the in vivo study. The reduction rate of PQ was checked out by measuring the PQ concentration in plasma before and after four hours of HP. Seeing the reduction rate was significantly higher in the survivors group than in the nonsurvivors group (80.39 ± 19.9 versus 67.29 ± 19.2%, P <0.01), we concluded that adequate HP appears to be an indispensable treatment for patients with acute PQ poisoning.

Toxicokinetics of paraquat in Korean patients with acute poisoning

To conduct a kinetic study of paraquat (PQ), we investigated 9 patients with acute PQ intoxication. All of them ingested more than 20 ml of undiluted PQ herbicide to commit suicide and arrived at our hospital early, not later than 7 h after PQ ingestion. The urine dithionite test for PQ in all of the nine patients was strongly positive at emergency room. Blood samples were obtained every 30 min for the first 2~3 h and then every 1 or 2 h, as long as the clinical progression was stable among the patients for 30 h after PQ ingestion. The area under the plasma concentration-time curve (AUC_inf), which was extrapolated to infinity, was calculated using the trapezoidal rule. Toxicokinetic parameters, such as the terminal elimination half-life, apparent oral clearance, and apparent volume of distribution (V_d/F) were calculated. The maximum PQ concentration (C_max) and the time to reach maximum PQ concentration (T_max) were also obtained. Plasma PQ concentrations in nine patients were well described by a bi-exponential curve with a mean terminal elimination half-life of 13.1±6.8 h. C_max and AUC_inf were 20.8±25.7 mg/l and 172.5±160.3 h·mg/l, respectively. Apparent volume of distribution and apparent oral clearance were 50.9±61.3 l/kg and 173.4±111.2 l/h, respectively. There were a significant correlation (r =0.84; p<0.05) between the PQ amount ingested and C_max. AUC_inf also showed a significant correlation (r =0.83; p<0.05) with the PQ amount ingested. These correlations provide evidence that PQ has dose-linear toxicokinetic characteristics.

Addition of immunosuppressive treatment to hemoperfusion is associated with improved survival after paraquat poisoning: a nationwide study

Paraquat poisoning associates very high mortality rate. Early treatment with hemoperfusion is strongly suggested by animal and human studies. Although the survival benefit of additional immunosuppressive treatment (IST) in combination with hemoperfusion is also reported since 1971, the large-scale randomized control trials to confirm the effects of IST is difficult to be executed. Therefore, we designed this nationwide large-scale population-based retrospective cohort study to investigate the outcome of paraquat poisoning with hemoperfusion and the additional effects of IST combined with hemoperfusion. This nationwide retrospective cohort study utilized data retrieved from the National Health Insurance Research Database (NHIRD) of Taiwan. A total of 1811 hospitalized patients with a diagnosis of paraquat poisoning who received hemoperfusion between 1997 and 2009 were enrolled. The mean age of all 1811 study subjects was 47.3 years. 70% was male. The overall survival rate was only 26.4%. Respiratory failure and renal failure were diagnosed in 56.2% and 36% patients. The average frequency of hemoperfusion was twice. IST was added in 42.2% patients. IST significantly increases survival rate (from 24.3% to 29.3%, P<0.001). The combined IST with methylprednisolone, cyclophosphamide and dexamethasone associates with the highest survival rate (48%, P<0.001). Moreover, patients younger than 45 years of age in the IST group had the best survival (41.0% vs. 33.7%, p<0.001). Our results support the use of IST with hemoperfusion for paraquat-poisoned patients. The best survival effect of IST is the combination of methylprednisolone, cyclophosphamide and daily dexamethasone, especially in patients with younger age.

New formulation of paraquat with lysine acetylsalicylate with low mammalian toxicity and effective herbicidal activity

BACKGROUND

Currently, the commercial formulations of the herbicide paraquat are highly toxic to humans, and no effective antidote is available for paraquat poisoning. The aim of the present study was to develop a safe formulation, combining paraquat and the known antidote lysine acetylsalicylate. The toxicity of a mixture of Gramoxone® (20% paraquat) and lysine acetylsalicylate in adult Wistar male rats and the herbicidal efficacy against grass lawn (50% of Poa pratensis and 50% of Festuca arundinacea) were evaluated. This new formulation was administered to Wistar rats by gavage at 125 mg kg(-1) of paraquat ion and lysine acetylsalicylate at 79, 158 or 316 mg kg(-1) body weight, and the survival rate was observed for 30 days.

RESULTS

The survival rate of the paraquat group was only 40%, while lysine acetylsalicylate provided effective protection, with full survival observed in the groups that received 125 mg kg(-1) of paraquat ion and 316 mg kg(-1) of lysine acetylsalicylate. Both formulations of paraquat, either in the absence or in the presence of lysine acetylsalicylate, provided the same herbicidal activity against the tested herbal species.

CONCLUSIONS

The present formulation of paraquat containing lysine acetylsalicylate, significantly decreases mammalian toxicity while maintaining effective herbicidal activity.

Paraquat intoxication in subjects who attempt suicide: why they chose paraquat

BACKGROUND/AIMS

Paraquat (PQ) has been used in suicide attempts; an estimated 2,000 toxic ingestions occur annually, with 60-70% mortality. We sought to determine why PQ is such a common agent for suicide attempts in Korea.

METHODS

We analyzed 250 cases (143 males, 107 females) of attempted suicide by PQ ingestion from January to December 2007. The procurement of the PQ was divided into two categories: purchased and preexisting.

RESULTS

Men were more likely to have purchased PQ than women (66% vs. 22%, p=0.042). Additionally, men were more likely to be unmarried (n=34, 23.9% vs. n=10, 9.3%) or divorced or separated (n=16, 11.3% vs. n=5, 4.6%) than the women (p<0.001). The group who intentionally selected PQ (38.4%) consisted of 96 cases (54 males, 42 females) and the group who did not intentionally select PQ (61.6%) included 154 cases (89 males, 65 females). The incidence of PQ purchase was higher in the intentional selection PQ group (46.9% vs. 18.2%, p<0.01).

CONCLUSIONS

Only 38% of patients who attempted suicide with PQ intentionally selected PQ. Thus, greater control of PQ availability is needed, especially in patients at risk.

The area of ground glass opacities of the lungs as a predictive factor in acute paraquat intoxication

Even though plasma paraquat (PQ) levels have known to be an informative predictor, many patients succumb at low PQ levels in acute PQ intoxication. This study was designed to see whether the high resolution computerized tomography (HRCT) of the lungs would be a predictive measure in acute PQ intoxication. HRCT of the lungs was obtained from 119 patients with acute PQ intoxication on 7 days after PQ ingestion. The areas with ground glass opacities (GGOs) were evaluated at five levels with the area measurement tool of the picture archiving and communication systems. Among 119 patients, 102 survived and 17 died. The plasma PQ levels were significantly higher in the non-survivors than in the survivors (2.6+/-4.0 microg/mL vs. 0.2+/-0.4 microg/mL, P=0.02). The area with GGOs was 2.0+/-6.4% in the survivors and 73.0+/- 29.9% in the non-survivors (P<0.001). No patients survived when the area with GGOs was more than 40% but all of the patients survived when the area affected by GGOs was less than 20%. In conclusion, the area of GGOs is a useful predictor of survival in acute PQ intoxication, especially in patients with low plasma PQ levels.

Comparison between kidney and hemoperfusion for paraquat elimination

The mortality rate of acute paraquat (PQ) poisoning depends on the PQ concentration in the blood. It has been shown that the kidneys eliminate PQ effectively. However, early renal function deterioration is frequently observed in acute PQ intoxication. This study is designed to compare the efficacy of PQ elimination with hemoperfusion (HP) and kidneys, taking into account the functional deterioration of the kidneys. The amount of renal and HP excretion of PQ were measured during the procedure of HP in patients with acute PQ intoxication. The PQ clearance and the actual amount of PQ elimination by the HP cartridge during the HP procedure were 111+/-11 mL/min (range; 13.2-162.2 mL/min) and 251.4+/-506.3 mg (range; 4.6-1,655.7) each. While, the renal clearance and actual amount of renal elimination of PQ was 79.8+/-56.0 mL/min (range; 9.7-177.0) and 75.4+/-73.6 mg (range; 4.9-245.8). As the creatinine clearance decreased, the PQ elimination by HP was as effective as or more effective than the renal elimination. In conclusion, early HP must be provided for life saving treatment in patients with acute PQ intoxication.

Association between plasma paraquat level and outcome of paraquat poisoning in 375 paraquat poisoning patients

OBJECTIVES

Paraquat poisoning by ingestion is often fatal. Many studies have investigated treatment modalities and predictor parameters, but there is no standard treatment. Plasma paraquat concentration seems a valid predictable parameter of survival. In order to achieve uniform treatment, including extracorporeal elimination and antioxidant therapy, the outcome of paraquat poisoning based on plasma paraquat level needs to be investigated.

METHODS

This study included 375 paraquat poisoning patients who were diagnosed by means of plasma paraquat concentration within 24 hours after ingestion in the Institute of Pesticide Poisoning of Soonchunhyang University Cheonan Hospital, Korea, from January 2005 to December 2006. All patients were treated according to a uniform protocol including extracorporeal elimination and antioxidant therapy. Plasma paraquat concentration was measured by high-performance liquid chromatography.

RESULTS

The mean age of the paraquat-intoxicated patients was 48.42 +/- 6.75. One hundred ten patients (29.3%) survived. The upper limit of plasma paraquat concentration in survivors was 2.64 at 3 hour. All patients with plasma paraquat level above 3.44 died. The minimum paraquat level of the deaths was very low (0.12 microg/ml at 5 hours; 0.02 microg/ml at 12 hours; 0.01 microg/ml at 24 hours).

CONCLUSIONS

Our data showed that plasma paraquat concentration is good predictor of survivors but is not good predictor of non-survivors in the low plasma paraquat level.

Paraquat poisonings: mechanisms of lung toxicity, clinical features, and treatment

Paraquat dichloride (methyl viologen; PQ) is an effective and widely used herbicide that has a proven safety record when appropriately applied to eliminate weeds. However, over the last decades, there have been numerous fatalities, mainly caused by accidental or voluntary ingestion. PQ poisoning is an extremely frustrating condition to manage clinically, due to the elevated morbidity and mortality observed so far and due to the lack of effective treatments to be used in humans. PQ mainly accumulates in the lung (pulmonary concentrations can be 6 to 10 times higher than those in the plasma), where it is retained even when blood levels start to decrease. The pulmonary effects can be explained by the participation of the polyamine transport system abundantly expressed in the membrane of alveolar cells type I, II, and Clara cells. Further downstream at the toxicodynamic level, the main molecular mechanism of PQ toxicity is based on redox cycling and intracellular oxidative stress generation. With this review we aimed to collect and describe the most pertinent and significant findings published in established scientific publications since the discovery of PQ, focusing on the most recent developments related to PQ lung toxicity and their relevance to the treatment of human poisonings. Considerable space is also dedicated to techniques for prognosis prediction, since these could allow development of rigorous clinical protocols that may produce comparable data for the evaluation of proposed therapies.

Identification of an alginate-based formulation of paraquat to reduce the exposure of the herbicide following oral ingestion

The herbicide paraquat has been widely used throughout the world for almost 50 years and is important in sustainable agriculture. When used correctly the chemical poses no known risk to human health. However, it is acutely toxic, and can be fatal, if the concentrated product is ingested orally. Despite many years of research there is no successful treatment for paraquat intoxication. In recent years we have turned our attention to understanding how we can make the product safer, if it is accidentally or intentionally consumed. We present in this paper a novel approach aimed at safening the paraquat product, Gramoxone. Following our previous research on the site and mechanism of paraquat absorption from the gastrointestinal tract we have identified a new formulation of paraquat, Gramoxone INTEON that reduces the absorption of paraquat into the blood. This new formulation contains the polysaccharide, alginate, a natural product extracted from sea-weed. We have designed a preparation of paraquat and alginate with surfactants that is herbicidally active but has the unique property that it gels on contact with gastric acid in the stomach. The resulting mixture slows the dispersion and delivery of the toxic chemical to its site of absorption in the small intestine. Alginates also protect the mucosa against the damaging influence of topical gastric irritants, like paraquat. Our studies have shown that increasing the loading of alginate between 7 and 17 g/L causes a dose-related reduction in paraquat absorption in vitro in isolated rat ileum. This is also observed in vivo, as measured by paraquat plasma kinetics in the rabbit where the Area Under Curve (AUC 0-24h) was reduced from 33.8+/-3 for Gramoxone to 12.5+/-6 (microg/mL)h for a formulation containing 17 g/L alginate. Such a reduction in systemic exposure to paraquat is expected to reduce the acute oral toxicity of the formulation. This should be particularly effective in a vomiting species such as man since we have shown in this investigation that alginates not only reduce the peak plasma paraquat values but also delay the time to peak levels. This provides the opportunity for a more effective emetic response since the highly viscous gelled material should remain in the stomach for longer than the liquid Gramoxone. Further research is required to understand and optimise the safening and herbicidal characteristics of these alginate acid-triggered gel formulations of paraquat. However, we anticipate that this alginate technology in Gramoxone INTEON could have significant benefit in reducing human mortalities associated with the herbicide.

P-glycoprotein induction: an antidotal pathway for paraquat-induced lung toxicity

The widespread use of the nonselective contact herbicide paraquat (PQ) has been the cause of thousands of deaths from both accidental and voluntary ingestion. The main target organ for PQ toxicity is the lung. No antidote or effective treatment to decrease PQ accumulation in the lung or to disrupt its toxicity has yet been developed. The present study describes a procedure that leads to a remarkable decrease in PQ accumulation in the lung, together with an increase in its fecal excretion and a subsequent decrease in several biochemical and histopathological biomarkers of toxicity. The administration of dexamethasone (100 mg/kg ip) to Wistar rats, 2 h after PQ intoxication (25 mg/kg ip), decreased the lung PQ accumulation to about 40% of the group exposed to only PQ and led to an improvement in tissue healing in just 24 h as a result of the induction of de novo synthesis of P-glycoprotein (P-gp). The involvement of P-gp in these effects was confirmed by Western blot analysis and by the use of a competitive inhibitor of this transporter, verapamil (10 mg/kg ip), which, given 1 h before dexamethasone, blocked its protective effects, causing instead an increase in lung PQ concentration and an aggravation of toxicity. In conclusion, the induction of P-gp, leading to a decrease in lung levels of PQ and the consequent prevention of toxicity, seems to be a new and promising treatment for PQ poisonings that should be further clinically tested.

Acute paraquat poisoning: report of a survival case following intake of a potential lethal dose

When properly used, paraquat (PQ) is a widely used bipyridil herbicide with a good safety record. Most cases of PQ poisoning result from intentional ingestion, with death resulting from hypoxemia secondary to lung fibrosis in moderate to severe poisonings. With high ingestion volumes (>50 mL of a 20% wt/vol formulation), death results from multiple organ failure and cardiovascular collapse within 1 week after intoxication. The present report describes a successful clinical case regarding the intoxication of a 15-year-old girl by a presumed lethal dose of PQ. The adolescent ingested approximately 50 mL of a commercialized concentrate (20% wt/vol of dichloride salt) formulation of PQ. High serum and urinary levels of PQ confirmed the bad prognosis. However, the therapeutic protocol followed in the present clinical case led to a positive outcome. Besides the measures for decreasing PQ absorption and increasing its elimination, other protective procedures were applied in aiming to reduce the production of reactive oxygen species (ROS), to scavenge ROS, to repair ROS-induced lesions, and to reduce inflammation. The status-of-the-art concerning the biochemical and toxicological aspects of PQ poisoning and the pharmacologic basis of the respective treatment is also presented.

Chapter 11.6 Clays and Clay Minerals as Drugs

This chapter discusses the applications of clays and clay materials as drugs. Clay minerals are efficient against several aggressors that cause major disorders of the gut. These beneficial effects of clay minerals (on the gastrointestinal mucosa) are associated with two mechanisms of action: (1) adsorption of the aggressors or their toxic secretions and (2) modification of the thickness and rheological properties of the adherent mucus, reinforcing the natural defenses of the gastrointestinal mucosa. At the surface of the gut, a mucus gel adheres to the epithelial cells of the mucosa. This adherent mucus is dynamic, being continuously secreted by the calceiform cells and regularly eroded by environmental aggressors present in the gut lumen. The mucus gel is largely composed of glycoprotein polymers, lipids, and proteins linked together by covalent bonds. It acts as a physical barrier protecting the mucosa against penetration by extraneous molecules and mechanical injury. By maintaining a pH gradient and competing with the epithelial surface for microorganisms, the mucus gel also acts as a chemical barrier.

Management of Lithium Toxicity

Lithium salts have been used in the prophylaxis and treatment of depression and bipolar disorder for >50 years. Lithium has a narrow therapeutic range, and several well characterised adverse effects limit the potential usefulness of higher doses. Acute ingestion in lithium-naive patients is generally associated with only short-lived exposure to high concentrations, due to extensive distribution of lithium throughout the total body water compartment. Conversely, chronic toxicity and acute-on-therapeutic ingestion are associated with prolonged exposure to higher tissue concentrations and, therefore, greater toxicity. Lithium toxicity may be life threatening, or result in persistent cognitive and neurological impairment. Therefore, enhanced lithium clearance has been explored as a means of minimising exposure to high tissue concentrations. Although haemodialysis is highly effective in removing circulating lithium, serum concentrations often rebound so repeated or prolonged treatment may be required. Continuous arteriovenous haemodiafiltration and continuous venovenous haemodiafiltration increase lithium clearance, albeit to a lesser extent than haemodialysis, and are more widely accessible. Haemodiafiltration sustained for >16 hours allows effective removal of total body lithium, thereby avoiding rebound effects. Enhanced elimination should be considered in patients at greatest risk of severe poisoning: namely those with chronic or acute-on-therapeutic toxicity, those with clinically significant features, and those with chronic toxicity whose serum lithium concentration is >2.5 mmol/L. The choice between haemodialysis and continuous haemodiafiltration techniques will depend on local accessibility and urgency of enhancing lithium elimination. Further research is required to establish the potential benefits of assisted elimination on clinical outcome in patients with lithium poisoning.

Pharmacokinetics of glutathione and its metabolites in normal subjects

To determine the loading and maintenance dosage of glutathione (GSH) for patients suffering from reactive oxygen species (ROS) injury such as acute paraquat intoxication, a kinetic study of reduced GSH was performed in synchrony with that of cysteine (Cys), cystine (Cys2), and methionine (Met). Human subject's porticipitation was voluntary. The effective dose of Cys, Cys2, and Met against ROS in fibroblast cells generated by paraquat was assessed using laser scanning confocal microscopy. Both Cys and Met suppressed ROS in a dose-dependent manner at concentrations of 1-1,000 microM; the concentration required to suppress ROS by 50% was 10 microM for Cys and 50 microM for Met. Using metabolite kinetics with the assumption that Cys and Met are the metabolites of GSH, expected concentrations of Cys and Met of above 20 and 50 microM were estimated when GSH was administered at 50 mg/kg body weights every 205.4 min for Cys and 427.4 min for Met.

The first line of response for people who self-poison: exploring the options for gut decontamination

The trend for increasing numbers of self-poisoning incidents has been noted and a variety of policy initiatives have been launched. Nurses, particularly in emergency room environments occupy a pivotal place in the chain of response to such acts. Any such response needs to be firmly rooted in evidence-based practice yet the initial management of self-poisoning often involves a consideration of procedures, the application of which can vary enormously. This paper offers some contextual information prior to a critical perspective of management modes, namely emesis, lavage, the use of activated charcoal and whole bowel irrigation. A comparison of the relative advantages and disadvantages of each mode precedes suggestions for nursing practice.

Successful single-lung transplantation after paraquat intoxication

Severe acute lung injury frequently develops after poisoning by paraquat, and respiratory failure is the major cause of death in patients surviving more than 2 days after ingestion. We describe a 17-year-old man with confirmed paraquat intoxication by lung and muscle biopsy, in whom single-lung transplantation was performed 44 days after poisoning for end-stage lung disease. The patient was discharged from the hospital 122 days after ingestion of paraquat and 88 days after lung transplantation. Before 1996, repeated lung transplantation had been performed for patients with terminal respiratory insufficiency due to paraquat toxicity, but all died. This patient survived probably because transplantation was performed very late after paraquat ingestion.

Effects of Fuller's Earth and activated charcoal on oral absorption of paraquat in rabbits

1. Thirty male rabbits of local strain (weighing 1.5-2 kg) were divided into five groups. Four groups were treated with an oral dose of paraquat, which was followed by either Fuller's Earth or activated charcoal 0.5 or 2.0 h later. The remaining group acted as the control group and was treated only with an oral dose of paraquat. The dose of paraquat was 20.0 mg/kg given in a concentration of 20.0 mg/mL. 2. Both adsorbents were administered in 15 mL normal saline as a 30% slurry. Blood was sampled from the ear vein 0.5, 1, 2, 4, 8 and 24h after the administration of paraquat. 3. Paraquat concentration was determined spectophotometrically at 600 nm by comparing against a standard curve of paraquat obtained by the addition of standard paraquat into normal rabbit serum and extracting interfering substances with ether. 4. The results of the present study show that either adsorbent can bring down the serum paraquat level. There was no significant difference found in the effectiveness of either adsorbent. 5. It is concluded that the administration of an adsorbent as early as possible will help in the reduction of paraquat absorption from the gastrointestinal tract. 6. Activated charcoal is still effective in lowering serum paraquat concentration when given more than 1 h after ingestion of paraquat.

Liposomal alpha-tocopherol alleviates the progression of paraquat-induced lung damage

The present study was carried out to investigate the efficacy of liposome-associated alpha-tocopherol in treating pulmonary damage caused by paraquat exposure. alpha-Tocopherol liposomes (8 mg alpha-tocopherol/kg body weight) or plain liposomes were intratracheally instilled into the lungs of rats 24 h after paraquat treatment (20 mg/kg, ip); treated animals were killed 8, 24 or 48 h after administration of the liposomal preparations. Lungs of animals exposed to paraquat were extensively damaged as evidenced by an increase in lung weight and decreases in pulmonary angiotensin converting enzyme and alkaline phosphatase activities. Also, paraquat treatment resulted in a significant reduction in glutathione (GSH) concentration in the lung and an elevation in microsomal lipid peroxidation levels, as measured by the formation of diene conjugates. Treatment of paraquat-injected rats with plain liposomes did not significantly alter paraquat-induced changes of all parameters examined. On the other hand, treatment of rats with alpha-tocopherol liposomes, 24 h after paraquat administration, resulted in a significant increase in pulmonary alpha-tocopherol concentrations as well as a reduction in paraquat-induced changes in lipid peroxidation, GSH concentration, and lung angiotensin converting enzyme and alkaline phosphatase activities. The results of the present study suggest that alpha-tocopherol, administered directly to the lung in a liposomal form, may serve as a potentially effective pharmacological agent in the treatment of paraquat-induced lung injury.

Inhaled nitric oxide in advanced paraquat intoxication

No effective treatment is available for adult respiratory distress syndrome, pulmonary hypertension and progressive lung fibrosis in severe paraquat poisoning. A potentially beneficial effect of nitric oxide inhalation on the mean pulmonary artery pressure and gas exchange in a subject with advanced paraquat intoxication is reported. Eight days after the suicidal ingestion of an unknown dose of paraquat, a 52-year-old female had a PaO2 < or = 50 mm Hg despite ventilation with an FiO2 of 1 and a positive end-expiratory pressure of 14 to 18 cm H2O. After administration of 25 ppm nitric oxide, PaO2 increased and the mean pulmonary artery pressure and the right-to-left shunt decreased. Discontinuation of nitric oxide resulted in rapid reversal. Ventilatory function was stabilized for three days during nitric oxide inhalation but the patient developed massive pleural effusions and died on d 11 during an interruption of nitric oxide therapy. The response of serious paraquat intoxications to nitric oxide therapy may merit further study. A remarkable post-mortem finding was extensive myonecrosis supporting prolonged muscular retention of paraquat with toxic myopathy or neuromyopathy as a late manifestation of paraquat toxicity.

Protective effect of liposome-associated alpha-tocopherol against paraquat-induced acute lung toxicity

The present study was undertaken to investigate whether alpha-tocopherol, entrapped in liposomes and delivered directly to the lung, could protect against paraquat-induced lung damage in the rat. Plain liposomes (composed of dipalmitoylphosphatidylcholine, DPPC) or DPPC/alpha-tocopherol liposomes were administered intratracheally to animals 24 hr prior to an intraperitoneal injection of paraquat (20 mg/kg); rats were killed 24 or 48 hr after paraquat treatment. Results of this study showed that lungs of animals treated with paraquat were damaged extensively as evidenced by an increase in lung weight and a significant reduction in lung angiotensin-converting enzyme (ACE) activity and cytochrome P450 concentration. Furthermore, paraquat treatment resulted in a significant decrease in reduced glutathione (GSH) concentrations and a marked elevation in microsomal lipid peroxidation levels as measured by the formation of diene conjugates. Pretreatment of rats with DPPC liposomes alone did not alter significantly the paraquat-induced changes of all parameters examined. On the other hand, pretreatment of rats with DPPC/alpha-tocopherol liposomes 24 hr prior to paraquat challenge resulted in a significant increase in pulmonary alpha-tocopherol concentrations and antagonized paraquat-induced changes in lipid peroxidation, GSH/GSSG ratio, lung ACE activity and cytochrome P450 concentrations. Results of this study suggested that alpha-tocopherol, delivered directly to the lung in a liposomal formulation 24 hr prior to paraquat administration, confers protection against paraquat-induced lung damage.

Gastrointestinal absorption of paraquat in the isolated mucosa of the rat

The gastrointestinal absorption of paraquat (1,1'-dimethyl-4,4'-bipyridylium) was studied using the isolated mucosa from different regions of the gastrointestinal tract of rats. Tissues were stripped of their muscle layers and the viability of the mucosa was maintained in flux chambers by bathing both serosal and luminal membranes with separate oxygenated solutions. Paraquat absorption, transmucosal potential difference (PD), and permeability of the mucosa were studied. Exposure of the luminal side of isolated mucosae to paraquat (100 mg/ml) resulted in greater paraquat absorption across the small intestine compared to other regions of the gastrointestinal tract. The descending order of tissue absorption (as %/cm2 mucosa) was jejunum (17.6 +/- 0.8%), ileum (10 +/- 2.7%), colon (5.7 +/- 3.2%), duodenum (5.5 +/- 1.3%), stomach (2 +/- 0.8%), and esophagus (0.5 +/- 0.7%). Mucosal uptake of paraquat in the ileum was nonlinear over a luminal concentration range 2-200 mg/ml. Three phases to paraquat absorption were identified in this region of the small intestine: (i) a rate which was faster than diffusion (2-20 mg/ml paraquat); (ii) a rate which was slower than diffusion and obeyed saturation kinetics, with an apparent Km = 116 mM and Vmax = 11.3 mumol/g/hr, at paraquat concentrations up to 150 mg/ml: and (iii) a rate similar to that of diffusion at 200 mg/ml paraquat. Paraquat absorption at 200 mg/ml was also associated with an increase in mucosal permeability and reduction in PD. Inhibition of tissue metabolism resulted in a linear or diffusional paraquat absorption over a wide luminal concentration range (2-200 mg/ml). It is suggested, therefore, that paraquat absorption in the rat occurs principally in the small intestine and by a mechanism which consists of facilitated, saturable, and diffusional components. Knowledge of the mechanism by which paraquat gains entry to the bloodstream may offer new approaches to the development of safer formulations of the herbicide.

Pre-embarkment prognostication for acute paraquat poisoning

1. In order to assess which laboratory parameters could be related to the prognosis of patients with acute paraquat poisoning, we reviewed the medical records of 160 patients who had ingested paraquat in an attempt at suicide. 2. Serum creatinine and potassium concentrations, arterial blood bicarbonate and base excess levels, arterial blood pH, volume of paraquat ingested and the strength of the urinary paraquat qualitative test (sodium dithionate colour reaction) on admission in the surviving patients were significantly different from those of the patients who died within 48 h of ingestion. 3. The relationship of the quantity Eq1 defined as: Eq1 = ([K+] x [HCO3-])/([Cre] x 0.088) (mEq l-1) against the interval of time after ingestion to admission (T) had a significant correlation with prognosis (P less than 0.01). Patients with Eq1 greater than (1500 - 399 X LogT) had a 90% survival rate, Eq1: (930 - 399 X LogT) less than Eq1 less than or equal to (1500 - 399 X LogT) 38% and Eq1 less than or equal to (930 - 399 X LogT) 3%, P less than 0.01.

Paraquat poisoning. An overview of the current status

Paraquat is a bipyridyl compound with no known chronic toxicity or teratogenicity. It is poorly absorbed when inhaled, but causes severe illness when ingested orally, death usually occurring within 2 days of ingestion of 50 mg/kg. At lower doses death may be delayed for several weeks. The toxic compound accumulates in lung tissue where free radicals are formed, lipid peroxidation is induced and nicotinamide adenine dinucleotide phosphate (NADPH) is depleted. This produces diffuse alveolitis followed by extensive pulmonary fibrosis. The most important prognostic indicator is the quantity of paraquat absorbed, as shown by the plasma paraquat concentration. While renal failure will develop in the majority of those patients who eventually die, it may not, if present alone, indicate a fatal outcome. The absence of caustic burns in the upper digestive tract indicates a good prognosis. Treatment of paraquat poisoning remains ineffective, but Fuller's earth, activated charcoal and resins may prevent some absorption of the toxin. When tubular necrosis occurs, renal excretion of the compound decreases rapidly. A 3-compartment pharmacokinetic model has been described following ingestion of tracer doses including a 'deep' compartment for active pulmonary accumulation. Haemodialysis, haemoperfusion and forced dialysis have been attempted, with no clear improvement in survival rates. Superoxide dismutase, glutathione peroxidase, N-acetylcysteine and other 'free radical scavengers' have failed to alter the outcome in poisoned patients. Other theoretical treatments, such as deferoxamine, immunotherapy, NADPH repletion and lung transplantation still require clinical validation.

Toxicokinetics of paraquat in humans

1. The toxicokinetics of paraquat were studied in 18 cases of acute human poisoning using a specific radioimmunoassay. Plasma paraquat concentration exhibited a mean distribution half-life (t1/2 alpha) of 5 h and a mean elimination half-life (t1/2 beta) of 84 h. Cardiovascular collapse supervened early during the course of the intoxication and was associated with the distribution phase. Death related to pulmonary fibrosis occurred late and was associated with the elimination phase. 2. Pharmacokinetic analysis of urine paraquat excretion confirmed the biphasic decline of paraquat. Moreover, renal paraquat and creatinine clearances were not correlated but renal paraquat clearance was never higher than the renal creatinine clearance. 3. Tissue paraquat distribution was ubiquitous with an apparent volume of distribution ranging from 1.2 to 1.6 l/kg. Muscle could represent an important reservoir explaining the long persistence of paraquat in plasma and urine for several weeks or months after poisoning.

Mechanistic studies: their role in the toxicological evaluation of pesticides

To date, studies on the mechanism of toxicity of pesticides are not yet an integral part of the toxicological evaluation process. However, in recent years mechanistic studies have played an increasing role in the assessment of toxicological hazards to man, and in this paper we have described two examples where an understanding of mechanism has contributed positively to risk assessment or has provided a surer scientific basis for the judgement of whether a potential hazard will be expressed in man. In the first example, an evaluation of the scientific literature leads to the conclusion that hepatic peroxisome proliferation in rats and mice is directly, or indirectly, related to the development of hepatocellular tumours. A wide range of non-mutagenic chemicals elicit peroxisome proliferation in mouse and rat liver, but not the guinea pig or marmoset liver. Using one of the diphenyl ether herbicides, fomesafen, we have shown that isolated hepatocytes from mice and rats, but not those from guinea pigs, marmosets and significantly man, undergo peroxisome proliferation. Therefore, it seems reasonable to conclude that although fomesafen causes peroxisome-related tumours in the mouse, man is neither susceptible nor sensitive to this mechanism. Consequently, we can conclude that fomesafen will not cause liver tumours in humans exposed to this herbicide. The herbicide paraquat, although safe in normal agricultural use, has been responsible for numerous human fatalities, almost exclusively as a result of the intentional ingestion of the concentrated commercial product.(ABSTRACT TRUNCATED AT 250 WORDS)

Repeated hemoperfusion and continuous arteriovenous hemofiltration in a paraquat poisoned patient

Prompt hemodialysis or hemoperfusion can be of value during the first 24 hours after paraquat ingestion particularly when the patient has developed acute renal failure. However, many cases of paraquat poisoning occur in areas where hemoperfusion facilities are unavailable. In contrast, continuous arteriovenous hemofiltration (CAVH) could be instituted easily. We have measured the removal of paraquat from the body by CAVH in a 46 year old male cane farmer who ingested 70 ml, 20% paraquat and died twelve days later from pulmonary fibrosis. Renal failure developed rapidly. Concentrations of paraquat were measured by an indirect competitive ELISA using a murine paraquat monoclonal IgG antibody. Hemoperfusion was performed daily for five days, beginning 78 hours post-ingestion. By 180 hours, when the patient was in respiratory failure, hemoperfusion was replaced with CAVH which was continued for 46 hours. During this time interval, 1.1 mg paraquat was recovered in the hemofiltrate and 1.56 mg paraquat in the urine. The extraction of paraquat by the hemofilter was close to 100%. The plasma clearance of paraquat across the hemofilter was 6.1 ml/min and the renal clearance was 8.2 ml/min. The mean hemoperfusion clearance of paraquat was 50 ml/min and the total amount of paraquat removed by the 34 hours of hemoperfusion was 9 mg. Because of the relative ease with which CAVH can be performed, its low cost, compared to that of hemoperfusion or hemodialysis, and the continuous nature of the procedure, CAVH may be worth considering in paraquat poisoning. It could be used particularly in those patients who have developed renal failure or while patients are being prepared for hemoperfusion.

Paraquat poisoning: clinical features and immediate general management

In contrast to 10-15 years ago most cases of paraquat poisoning are now due to deliberate self-poisoning with parasuicidal or suicidal intent rather than to accidental ingestion. Less commonly, poisoning may follow careless handling of paraquat during occupational use. Although paraquat can be absorbed through the skin if improperly handled, poisoning usually follows ingestion and has rarely been reported after subcutaneous, intravenous or intraperitoneal injection. Clinically, three degrees of intoxication may be distinguished. Mild poisoning occurs after the ingestion or injection of less than 20 mg of paraquat ion/kg body weight. In these cases patients are either asymptomatic or symptoms are confined to the gastrointestinal system. All patients recover fully. Moderate to severe poisoning usually follows the ingestion (rarely injection) of 20-40 mg of paraquat ion/kg body weight. Non-specific symptoms of ill health together with local gastrointestinal symptoms precede the development of renal failure (which may recover spontaneously) and pulmonary fibrosis which may not be manifest for days or weeks. Death occurs in the majority of cases but is usually delayed for 2-3 weeks. Acute fulminant poisoning follows the ingestion of substantial quantities of paraquat (greater than 40 mg of paraquat ion/kg body weight). In addition to local symptoms, multiple organ (cardiac, respiratory, hepatic, renal, adrenal, pancreatic, neurological) failure occurs. Death may supervene within hours and is never delayed for more than a few days. Initial general management has four priorities.(ABSTRACT TRUNCATED AT 250 WORDS)