N-Acetylcysteine--a safe antidote for cysteine/glutathione deficiency

Glutathione (GSH) deficiency is associated with numerous pathological conditions. Administration of N-acetylcysteine (NAC), a cysteine prodrug, replenishes intracellular GSH levels. NAC, best known for its ability to counter acetaminophen toxicity, is a safe, well-tolerated antidote for cysteine/GSH deficiency. NAC has been used successfully to treat GSH deficiency in a wide range of infections, genetic defects and metabolic disorders, including HIV infection and COPD. Over two-thirds of 46 placebo-controlled clinical trials with orally administered NAC have indicated beneficial effects of NAC measured either as trial endpoints or as general measures of improvement in quality of life and well-being of the patients.

Review of oximes in the antidotal treatment of poisoning by organophosphorus nerve agents

The cholinesterase-inhibiting organophosphorus compounds referred to as nerve agents (soman, sarin, tabun, GF agent, and VX) are particularly toxic and are considered to be among the most dangerous chemical warfare agents. Included in antidotal medical countermeasures are oximes to reactivate the inhibited cholinesterase. Much experimental work has been done to better understand the properties of the oxime antidotal candidates including the currently available pralidoxime and obidoxime, the H oximes HI-6 and Hlö-7, and methoxime. There is no single, broad-spectrum oxime suitablefor the antidotal treatment of poisoning with all organophosphorus agents. If more than one oxime is available, the choice depends primarily on the identity of the responsible organophosphorus compound. The H oximes appear to be very promising antidotes against nerve agents because they are able to protect experimental animals from toxic effects and improve survival of animals poisoned with supralethal doses. They appear more effective against nerve agent poisoning than the currently used oximes pralidoxime and obidoxime, especially in the case of soman poisoning. On the other hand, pralidoxime and especially obidoxime seem sufficiently effective to treat poisonings with organophosphorus insecticides that have relatively less toxicity than nerve agents.

Pralidoxime iodide (2-pAM) penetrates across the blood-brain barrier

The in vivo rat brain microdialysis technique with HPLC/UV was used to determine the blood-brain barrier (BBB) penetration of pralidoxime iodide (2-PAM), which is a component of the current nerve agent antidote therapy. After intravenous dosage of 2-PAM (10, 50, 100 mg/kg), 2-PAM appeared dose-dependently in the dialysate; the striatal extracellular/blood concentration ratio at 1 h after 50 mg/kg dosage was 0.093 +/- 0.053 (mean +/- SEM). This finding offered conclusive evidence of the BBB penetration of 2-PAM. We also examined whether the BBB penetration of 2-PAM was mediated by a certain specific transporter, such as a neutral or basic amino acid transport system. Although it was unclear, the neural uptake of 2-PAM was Na+ dependent. The mean BBB penetration by 2-PAM was approximately 10%, indicating the intravenous administration of 2-PAM might be to a degree effective to reactivation of the blocked cholinesterase in the brain.

Pralidoxime in acute organophosphorus insecticide poisoning--a randomised controlled trial

BACKGROUND

Poisoning with organophosphorus (OP) insecticides is a major global public health problem, causing an estimated 200,000 deaths each year. Although the World Health Organization recommends use of pralidoxime, this antidote's effectiveness remains unclear. We aimed to determine whether the addition of pralidoxime chloride to atropine and supportive care offers benefit.

METHODS AND FINDINGS

We performed a double-blind randomised placebo-controlled trial of pralidoxime chloride (2 g loading dose over 20 min, followed by a constant infusion of 0.5 g/h for up to 7 d) versus saline in patients with organophosphorus insecticide self-poisoning. Mortality was the primary outcome; secondary outcomes included intubation, duration of intubation, and time to death. We measured baseline markers of exposure and pharmacodynamic markers of response to aid interpretation of clinical outcomes. Two hundred thirty-five patients were randomised to receive pralidoxime (121) or saline placebo (114). Pralidoxime produced substantial and moderate red cell acetylcholinesterase reactivation in patients poisoned by diethyl and dimethyl compounds, respectively. Mortality was nonsignificantly higher in patients receiving pralidoxime: 30/121 (24.8%) receiving pralidoxime died, compared with 18/114 (15.8%) receiving placebo (adjusted hazard ratio [HR] 1.69, 95% confidence interval [CI] 0.88-3.26, p = 0.12). Incorporating the baseline amount of acetylcholinesterase already aged and plasma OP concentration into the analysis increased the HR for patients receiving pralidoxime compared to placebo, further decreasing the likelihood that pralidoxime is beneficial. The need for intubation was similar in both groups (pralidoxime 26/121 [21.5%], placebo 24/114 [21.1%], adjusted HR 1.27 [95% CI 0.71-2.29]). To reduce confounding due to ingestion of different insecticides, we further analysed patients with confirmed chlorpyrifos or dimethoate poisoning alone, finding no evidence of benefit.

CONCLUSIONS

Despite clear reactivation of red cell acetylcholinesterase in diethyl organophosphorus pesticide poisoned patients, we found no evidence that this regimen improves survival or reduces need for intubation in patients with organophosphorus insecticide poisoning. The reason for this failure to benefit patients was not apparent. Further studies of different dose regimens or different oximes are required.

The antidotal action of sodium nitrite and sodium thiosulfate against cyanide poisoning

The combination of sodium thiosulfate and sodium nitrite has been used in the United States since the 1930s as the primary antidote for cyanide intoxication. Although this combination was shown to exhibit much greater efficacy than either ingredient alone, the two compounds could not be used prophylactically because each exhibits a number of side effects. This review discusses the pharmacodynamics, pharmacokinetics, and toxicology of the individual agents, and their combination.

Refinement of structural leads for centrally acting oxime reactivators of phosphylated cholinesterases

We present a systematic structural optimization of uncharged but ionizable N-substituted 2-hydroxyiminoacetamido alkylamine reactivators of phosphylated human acetylcholinesterase (hAChE) intended to catalyze the hydrolysis of organophosphate (OP)-inhibited hAChE in the CNS. Starting with the initial lead oxime RS41A identified in our earlier study and extending to the azepine analog RS194B, reactivation rates for OP-hAChE conjugates formed by sarin, cyclosarin, VX, paraoxon, and tabun are enhanced severalfold in vitro. To analyze the mechanism of intrinsic reactivation of the OP-AChE conjugate and penetration of the blood-brain barrier, the pH dependence of the oxime and amine ionizing groups of the compounds and their nucleophilic potential were examined by UV-visible spectroscopy, (1)H NMR, and oximolysis rates for acetylthiocholine and phosphoester hydrolysis. Oximolysis rates were compared in solution and on AChE conjugates and analyzed in terms of the ionization states for reactivation of the OP-conjugated AChE. In addition, toxicity and pharmacokinetic studies in mice show significantly improved CNS penetration and retention for RS194B when compared with RS41A. The enhanced intrinsic reactivity against the OP-AChE target combined with favorable pharmacokinetic properties resulted in great improvement of antidotal properties of RS194B compared with RS41A and the standard peripherally active oxime, 2-pyridinealdoxime methiodide. Improvement was particularly noticeable when pretreatment of mice with RS194B before OP exposure was combined with RS194B reactivation therapy after the OP insult.

Irinotecan combined with bolus fluorouracil, continuous infusion fluorouracil, and high-dose leucovorin every two weeks (LV5FU2 regimen): a clinical dose-finding and pharmacokinetic study in patients with pretreated metastatic colorectal cancer

PURPOSE

To determine the maximum-tolerated dose (MTD) and recommended dose of irinotecan (CPT-11) in combination with fluorouracil (5-FU) and leucovorin (LV), using a biweekly LV5FU2 regimen and increasing doses of CPT-11, and to assess the efficacy of this combination in pretreated patients with colorectal cancer (CRC).

PATIENTS AND METHODS

All patients had metastatic CRC and a World Health Organization performance status of 0 or 1. CPT-11 was administered over a 90-minute infusion every 2 weeks at a range of dose levels (100, 120, 150, 180, 200, 220, and 260 mg/m(2)). LV5FU2 was started 1 hour after the end of the biweekly CPT-11 infusion and was also administered on day 2.

RESULTS

Fifty-five patients were entered onto this trial; 549 cycles were administered. The MTD was not reached at 260 mg/m(2), and a dose level of 300 mg/m(2) was added. The MTD as defined in the protocol was not reached at this dose level either, but all patients had cycles delayed and/or required a dose reduction. This dose was deemed to be the MTD. To take into account both the toxicity of and compliance with the biweekly schedule, the recommended CPT-11 dose was established at 180 to 200 mg/m(2). Antitumor activity was observed at almost all dose levels, with an objective response rate of 22%. Median time to progression was 6.3 months and overall survival was 15 months.

CONCLUSION

The biweekly CPT-11/LV5FU2 combination is feasible and safe, without overlapping toxicity. CPT-11 at 180 to 200 mg/m(2) in combination with LV5FU2 has been selected as the recommended dose for further studies.

Development of the Bisquaternary Oxime HI-6 Toward Clinical Use in the Treatment of Organophosphate Nerve Agent Poisoning

The traditional therapeutic treatment of organophosphate cholinesterase inhibitor (nerve agents) poisoning consists of co-treatment with an antimuscarinic (atropine) and a reactivator of inhibited acetylcholinesterase (AChE), which contains a nucleophilic oxime function. Two oximes are presently widely available for clinical use, pralidoxime and obidoxime (toxogonin), but both offer little protection against important nerve agent threats. This has highlighted the real need for the development and availability of more effective oximes for human use, a search that has been going on for up to 30 years. However, despite the demonstration of more effective and safe oximes in animal experiments, no additional oximes have been licensed for human use. HI-6, (1-[[[4(aminocarbonyl)-pyridinio]methoxy]methyl]-2(hydroxyimino)pyridinium dichloride; CAS 34433-31-3) has been studied intensively and has been proved effective in a variety of species including non-human primates and appears from clinical experience to be safe in humans. These studies have led to the fielding of HI-6 for use against nerve agents by the militaries of the Czech republic, Sweden, Canada and under certain circumstances the Organisation for the Prohibition of Chemical Weapons. Nevertheless HI-6 has not been granted a license for clinical use, must be used only under restricted guidelines and is not available for civilian use as far as is known. This article will highlight those factors relating to HI-6 that pertain to the licensing of new compounds of this type, including the mechanism of action, the clinical and pre-clinical demonstration of safety and its efficacy against a variety of nerve agents particularly in non-human primates, since no relevant human population exists. This article also contains important data on the use of HI-6 in baboons, which has not been available previously. The article also discusses the possibility of successful therapy with HI-6 against poisoning in humans relative to doses used in non-human primates and relative to its ability to reactivate inhibited human AChE.

Selective neuronal vulnerability following mild focal brain ischemia in the mouse

The evolution of cellular damage over time and the selective vulnerability of different neuronal subtypes was characterized in the striatum following 30-minute middle cerebral artery occlusion and reperfusion in the mouse. Using autoradiography we found an increase in the density of [3H]PK11195 binding sites--likely reflecting microglial activation--in the lesion border at 3 days and in the whole striatum from 10 days to 6 weeks. This was accompanied by a distinct loss of [3H]flumazenil and [3H]CGP39653 binding sites from 10 days up to 6 weeks reflecting neuronal loss. Brain ischemia resulted in a substantial loss of medium spiny projection neurons as seen at three days by Nissl staining, TUNEL and immunocytochemistry using antibodies against microtubule-associated protein (MAP2), NeuN, mu-opioid receptors, substance P, L-enkephalin, neurokinin B, choline acetyltransferase, parvalbumin, calretinin and somatostatin. Both patch and matrix compartments were involved in ischemic damage. In contrast, the numbers of cholinergic, GABAergic, and somatostatin-containing interneurons in the ischemic striatum were not different from those in the contralateral hemisphere at 3 and 14 days. A low density of glutamate receptors, the ability to sequester calcium by calcium-binding proteins and other hitherto unidentified factors may explain this relative resistance of interneurons to acute ischemia.

Chemical and Biological Considerations in the Treatment of Metal Intoxications by Chelating Agents

Effective chelation treatment of metal intoxications requires that the pharmacokinetics of the administered chelator in fact leads to chelation of the toxic metal, preferably forming a less toxic species which is effectively excreted. This depends on physical and chemical characteristics of metals and chelators as e.g. ionic diameter, ring size and deformability, hardness/softness of electron donors and acceptors, administration route, bioavailability, metabolism, organ and intra/extra cellular compartmentalization, and excretion. In vivo chelation is unlikely to reach equilibrium determined by the standard stability constant, as rate effects and ligand exchange reactions as well as the pharmacokinetics of the chelator considerably influence complex formation. Hydrophilic chelators enhance renal metal excretion, but mainly their extracellular distribution limit their effect to mainly extracellular metal pools. Lipophilic chelators can decrease intracellular stores, but may redistribute toxic metals to e.g. the brain. In chronic metal induced disease, necessitating life-long chelation, toxicity and side effects of the chelator may limit the treatment. The metal selectivity of chelators is important, due to the risk of essential metals depletion. Dimercaptosuccinic acid and dimercaptopropionic sulfonate are presently gaining increased acceptance among clinicians, undoubtedly improving the management of human metal intoxications including lead, arsenic and mercury compounds. Still, development of new safer chelators suited for long-term oral administration for chelation of metal deposits, mainly iron, is an important challenge to the future research.

Prussian blue for treatment of radiocesium poisoning

Prussian blue is a crystal lattice that exchanges potassium for cesium at the surface of the crystal. When given orally, it binds cesium that is secreted in the gut before it can be reabsorbed. Data suggest that in humans, Prussian blue can reduce cesium's half-life by approximately 43% and reduce total body burdens. Prussian blue is well tolerated at a dosage of 3 g/day with appropriate monitoring of serum potassium levels and observing for signs of constipation. Clinical data on the efficacy of Prussian blue in the management of radiocesium poisoning were evaluated. Articles published in English describing distribution and elimination of cesium in both humans and animals were reviewed, along with articles describing administration of Prussian blue in clinical toxicology.

Pharmacokinetics and effects of HI 6 in blood and brain of soman-intoxicated rats: a microdialysis study

The bispyridinium oxime HI 6 (1-(((4-amino-carbonyl)pyridino)methoxy)methyl)-2-(hydroxyimino )methyl)-pyridinium dichloride monohydrate), combined with atropine, is effective for treating poisoning with organophosphate nerve agents. The protective action of HI 6 in soman poisoning has been attributed mainly to its peripheral reactivation of inhibited acetylcholinesterase. In the present study we investigated whether high intramuscular doses of HI 6 can reach the brain in a sufficient amount to reactivate inhibited brain acetylcholinesterase. Microdialysis probes were implanted in the jugular vein and striatum and dialysis samples were collected simultaneously from the two sites in awake, freely moving rats. Pharmacokinetic parameters of unbound HI 6 in blood and brain were calculated after administration of HI 6 (50, 75 or 100 mg/kg i.m.) in control rats and rats injected with soman (90 microg/kg s.c., 0.9 LD50) 1 min before HI 6 treatment. We found that signs of soman poisoning correlated positively to acetylcholinesterase inhibition and negatively to the concentration of unbound HI 6 in the brain and that soman intoxication significantly decreased uptake of HI 6 into the brain.

Are we ready to replace dimercaprol (BAL) as an arsenic antidote?

1 Dimercaprol (BAL), 2,3-dimercaptopropanesulphonate sodium (DMPS) and meso-2,3-dimercaptosuccinic acid (DMSA) are effective arsenic antidotes, but the question which one is preferable for optimal therapy of arsenic poisoning is still open to discussion. Major drawbacks of BAL include (a) its low therapeutic index, (b) its tendency to redistribute arsenic to brain and testes, for example, (c) the need for (painful) intramuscular injection and (d) its unpleasant odour. 2 The newer antidotes DMPS and DMSA feature low toxicity and high therapeutic index. They can be given orally or intravenously due to their high water solubility. While these advantages make it likely that DMPS and DMSA will replace BAL for the treatment of chronic arsenic poisoning, acute intoxication-especially with lipophilic organoarsenicals-may pose a problem for the hydrophilic antidotes, because their ionic nature can adversely affect intracellular availability. 3 This article focuses on aspects dealing with the power of BAL, DMPS, and DMSA to mobilize tissue-bound arsenic in various experimental models, such as monolayers of MDCK (= Madin-Darby canine kidney) cells from dog kidney, isolated perfused liver from guinea-pigs, and perfused jejunal segments from rat small intestine. 4 The results show that hydrophilic DMPS and DMSA may fail to rapidly and completely remove arsenic that has escaped from the extracellular space across tight epithelial barriers. However, owing to their low toxicity, which allows larger doses to be applied, and the potential modification of their pharmacokinetics by means of inert oral anion-exchange resins, DMPS and DMSA may advantageously replace BAL whenever intervention time is not critical. With severe intoxication by organic arsenicals, when the point-of-no-return is a limiting factor, BAL may still have a place as an arsenic antidote.

AEOL10150: a novel therapeutic for rescue treatment after toxic gas lung injury

New therapeutics designed as rescue treatments after toxic gas injury such as from chlorine (Cl(2)) are an emerging area of interest. We tested the effects of the metalloporphyrin catalytic antioxidant AEOL10150, a compound that scavenges peroxynitrite, inhibits lipid peroxidation, and has SOD and catalase-like activities, on Cl(2)-induced airway injury. Balb/C mice received 100ppm Cl(2) gas for 5 min. Four groups were studied: Cl(2) only, Cl(2) followed by AEOL10150 1 and 9 h after exposure, AEOL10150 only, and control. Twenty-four hours after Cl(2) gas exposure airway responsiveness to aerosolized methacholine (6.25-50mg/ml) was measured using a small-animal ventilator. Bronchoalveolar lavage (BAL) was performed to assess airway inflammation and protein. Whole lung tissue was assayed for 4-hydroxynonenal. In separate groups, lungs were collected at 72 h after Cl(2) injury to evaluate epithelial cell proliferation. Mice exposed to Cl(2) showed a significantly higher airway resistance compared to control, Cl(2)/AEOL10150, or AEOL10150-only treated animals in response to methacholine challenge. Eosinophils, neutrophils, and macrophages were elevated in BAL of Cl(2)-exposed mice. AEOL10150 attenuated the increases in neutrophils and macrophages. AEOL10150 prevented Cl(2)-induced increase in BAL fluid protein. Chlorine induced an increase in the number of proliferating airway epithelial cells, an effect AEOL10150 attenuated. 4-Hydroxynonenal levels in the lung were increased after Cl(2) and this effect was prevented with AEOL10150. AEOL10150 is an effective rescue treatment for Cl(2)-induced airway hyperresponsiveness, airway inflammation, injury-induced airway epithelial cell regeneration, and oxidative stress.

A Synthetic Receptor as a Specific Antidote for Paraquat Poisoning

Accidental or suicidal ingestion of the world's most widely used herbicide, paraquat (PQ), may result in rapid multi-organ failure with a 60% fatality rate due to the absence of an effective detoxification solution. Effective, specific antidotes to PQ poisoning have been highly desired. Methods: The binding constant of PQ and a synthetic receptor, cucurbit[7]uril (CB[7]), was first determined in various pH environments. The antidotal effects of CB[7] on PQ toxicity were firstly evaluated with in-vitro cell lines. With in-vivo mice models, the pharmacokinetics and the biodistribution of PQ in major organs were determined to evaluate the influence of CB[7] on the oral bioavailability of PQ. Major organs' injuries and overall survival rates of the mice were systemically examined to evaluate the therapeutic efficacy of CB[7] on PQ poisoning. Results: We demonstrate that CB[7] may complex PQ strongly under various conditions and significantly reduce its toxicity in vitro and in vivo. Oral administration of PQ in the presence of CB[7] in a mouse model significantly decreased PQ levels in the plasma and major organs and alleviated major organs' injuries, when compared to those of mice administered with PQ alone. Further studies indicated that oral administration of CB[7] within 2 h post PQ ingestion significantly increased the survival rates and extended the survival time of the mice, in contrast to the ineffective treatment by activated charcoal, which is commonly recommended for PQ decontamination. Conclusion: CB[7] may be used as a specific oral antidote for PQ poisoning by strongly binding with PQ and inhibiting its absorption in the gastrointestinal tracts.

HI 6 human serum albumin nanoparticles--development and transport over an in vitro blood-brain barrier model

The standard treatment of intoxication with organophosphorus (OP) compounds includes the administration of oximes acting as acetylcholinesterase (AChE) reactivating antidotes. However, the blood-brain barrier (BBB) restricts the rapid transport of these drugs from the blood into the brain in therapeutically relevant concentrations. Since human serum albumin (HSA) nanoparticles enable the delivery of a variety of drugs across the BBB into the brain, HI 6 dimethanesulfonate and HI 6 dichloride monohydrate were bound to these nanoparticles in the present study. The resulting sorption isotherms showed a better fit to Freundlich's empirical adsorption isotherm than to Langmuir's adsorption isotherm. At the pH of 8.3 maximum drug binding capacities of 344.8 μg and 322.6 μg per mg of nanoparticles were calculated for HI 6 dimethanesulfonate and HI 6 dichloride monohydrate, respectively. These calculated values are higher than the adsorption capacity of 93.5 μg/mg for obidoxime onto HSA nanoparticles determined in a previous study. In vitro testing of the nanoparticulate oxime formulations in primary porcine brain capillary endothelial cells (pBCEC) demonstrated an up to two times higher reactivation of OP-inhibited AChE than the free oximes. These findings show that nanoparticles made of HSA may enable a sufficient antidote OP-poisoning therapy with HI 6 derivatives even within the central nervous system (CNS).

Pharmacokinetics following a loading plus a continuous infusion of pralidoxime compared with the traditional short infusion regimen in human volunteers

BACKGROUND

Many authors currently recommend infusing the adult dose (1 g) of pralidoxime over a 15-30 minute period. When administered in this manner, computer simulations predict that plasma pralidoxime concentrations will fall below 4 mg/L as early as one and one half hours after administration. The objective of this study was to assess whether a loading dose followed by a continuous infusion would maintain therapeutic levels longer than the traditional short infusion regimen of pralidoxime if the same total dose was administered.

METHODS

Utilizing a randomized, crossover design, healthy volunteers were administered either 16 mg/kg of pralidoxime intravenous over 30 minutes or 4 mg/kg of pralidoxime intravenous over 15 minutes followed by 3.2 mg/kg/h for 3.75 h (for a total dose of 16 mg/kg). Pralidoxime levels were obtained at 0, 10, 20, 30, 60, 120, 180, 240, 300, and 390 minutes and patients were observed for vital sign changes and adverse effects.

RESULTS

Seven subjects completed both arms of the study. One subject's data were excluded from pharmacokinetic analysis due to aberrant plasma pralidoxime analysis. The loading dose followed by the continuous infusion maintained therapeutic levels for 257.3 +/- 50.5 minutes whereas the short infusion maintained therapeutic levels for 118.1 +/- 52.1 (p < 0.001). Adverse effects were encountered during the short infusion regimen which did not occur during the continuous infusion. Dizziness or blurred vision occurred in all subjects during the short infusion regimen. Additionally, statistically significant increases in diastolic blood pressure occurred during the short infusion regimen.

CONCLUSIONS

The results of this study indicate that a loading dose followed by a continuous infusion of pralidoxime maintains therapeutic concentrations for a longer period of time than the currently recommended short infusion regimen in healthy volunteers.

Glutathione kinetics in normal man and in patients with liver cirrhosis

BACKGROUND/AIMS

The dynamics of glutathione in plasma has always been studied by bolus injections. Data are available suggesting that the low plasma levels of cirrhosis are due to decreased production in glutathione-producing tissues, mainly the liver. We aimed to measure the kinetics of glutathione during controlled steady-state conditions, and to determine the reasons for its reduced plasma levels in advanced cirrhosis.

METHODS

The plasma clearance of glutathione was measured in six control subjects and in ten patients with cirrhosis during a 2-step infusion study, producing steady-state levels approximately 5 and 10 times basal values. The plasma disappearance curve after infusion stop was used to determine the apparent volume of distribution and half-life of glutathione, and the estimated basal appearance rate.

RESULTS

The clearance of glutathione did not reject 1st-order kinetics, i.e., it was concentration-independent, and was nearly doubled in cirrhosis. The half-life of exogenous glutathione was not different, whereas the volume of distribution was larger in cirrhosis, in the same range as extracellular water. The endogenous basal appearance rate of glutathione was reduced by 50%, and correlated with liver function, measured by routine and dynamic tests.

CONCLUSIONS

The data confirm that the primary defect responsible for reduced glutathione in liver disease is a reduced production, possibly related to hepatocyte dysfunction and a block along the pathway of methionine metabolism.

Ethylene glycol poisoning in a child treated with 4-methylpyrazole

OBJECTIVE

The alcohol dehydrogenase inhibitor 4-methylpyrazole (4-MP) is a new antidote of ethylene glycol (EG) intoxication. The purpose of the present case report was to demonstrate 4-MP efficiency in EG poisoning in a 4-year-old child.

METHOD AND RESULTS

4-MP Treatment was performed 7 hours after EG ingestion. Plasma EG and 4-MP concentrations were measured 2 hours after each infusion of 4-MP. Plasma 4-MP concentrations were in the range of the values reported to block EG metabolism. The efficiency of 4-MP treatment was confirmed by the rapid correction of metabolic acidosis without alkalization and by the increase in EG half-life. No adverse effect of 4-MP was observed.

CONCLUSION

This child ingested a potentially lethal dose of EG despite a high concentration of bittering agent in antifreeze. EG poisoning was treated efficiently by 4-MP without recourse to hemodialysis.

Pharmacology, Pharmacokinetics, and Tissue Disposition of Zwitterionic Hydroxyiminoacetamido Alkylamines as Reactivating Antidotes for Organophosphate Exposure

In the development of antidotal therapy for treatment of organophosphate exposure from pesticides used in agriculture and nerve agents insidiously employed in terrorism, the alkylpyridinium aldoximes have received primary attention since their early development by I. B. Wilson in the 1950s. Yet these agents, by virtue of their quaternary structure, are limited in rates of crossing the blood-brain barrier, and they require administration parenterally to achieve full distribution in the body. Oximes lacking cationic charges or presenting a tertiary amine have been considered as alternatives. Herein, we examine the pharmacokinetic properties of a lead ionizable, zwitterionic hydroxyiminoacetamido alkylamine in mice to develop a framework for studying these agents in vivo and generate sufficient data for their consideration as appropriate antidotes for humans. Consequently, in vitro and in vivo efficacies of immediate structural congeners were explored as leads or backups for animal studies. We compared oral and parenteral dosing, and we developed an intramuscular loading and oral maintenance dosing scheme in mice. Steady-state plasma and brain levels of the antidote were achieved with sequential administrations out to 10 hours, with brain levels exceeding plasma levels shortly after administration. Moreover, the zwitterionic oxime showed substantial protection after gavage, whereas the classic methylpyridinium aldoxime (2-pyridinealdoxime methiodide) was without evident protection. Although further studies in other animal species are necessary, ionizing zwitterionic aldoximes present viable alternatives to existing antidotes for prophylaxis and treatment of large numbers of individuals in terrorist-led events with nerve agent organophosphates, such as sarin, and in organophosphate pesticide exposure.

Pharmacokinetics of hydroxocobalamin in smoke inhalation victims

OBJECTIVE

Hydroxocobalamin has been proposed as a cyanide antidote. Little is known, however, about its pharmacokinetics in human cyanide poisoning.

METHODS

We prospectively studied the pharmacokinetics of hydroxocobalamin in 11 smoke inhalation victims of whom all but one had objective evidence of cyanide exposure. Serum hydroxocobalamin levels were followed from just before drug administration to six days after a single 5 g dose of hydroxocobalamin.

RESULTS

The results (mean +/- standard error) suggest a two compartment model. Distribution half-life is on the order of 1.86 +/- 0.34 h and the elimination half-life 26.2 +/- 2.7 h. The apparent volume of distribution is 0.45 +/- 0.03 L/kg. Renal and total body clearance are 0.31 +/- 0.06 and 0.83 +/- 0.07 L/h, respectively.

CONCLUSION

The apparent volume of distribution suggests a predominantly extracellular partitioning of the antidote, even in the presence of cyanide, an important factor in terms of its antidotal effect. Hydroxocobalamin's elimination half-life in these cyanide-exposed patients far exceeds those found in previous studies of dogs and minimally-exposed humans. If confirmed, this half-life suggests that a single dose of hydroxocobalamin, sufficiently large enough to bind the cyanide present, should be adequate.

Preclinical safety and efficacy of andexanet alfa in animal models

Essentials There is currently no approved reversal agent for factor Xa (FXa) inhibitors Andexanet alfa has been developed to reverse the anticoagulant effects of FXa inhibitors Andexanet reduced blood loss and anticoagulation markers in rivaroxaban-anticoagulated rabbits Andexanet was well tolerated in monkeys and rats, with no evidence of prothrombotic activity SUMMARY: Background Andexanet alfa is a recombinant modified form of factor Xa (FXa), designed to bind to and reverse the anticoagulant activity of FXa inhibitors. Objectives To evaluate the ability of andexanet to reverse the anticoagulant activity of rivaroxaban, and assess its pharmacokinetics (PK) and toxicity in animal models. Methods The effects of andexanet on blood loss, anti-FXa activity, rivaroxaban unbound plasma concentrations and other coagulation parameters were assessed in a rabbit liver laceration 'treatment' model. Andexanet was administered 10 min after blood loss was initiated. The toxicity of repeated administration of andexanet (up to 60 mg kg-1 day-1 ) was assessed in cynomolgus monkeys. PK parameters were evaluated in rats and monkeys. Results Excess blood loss due to anticoagulation with rivaroxaban was significantly decreased by a single intravenous bolus administration of andexanet at 35 and 75 mg per rabbit, by 75% and 63%, respectively. This correlated with dose-dependent decreases in the unbound fraction of rivaroxaban and anti-FXa activity. Co-administration of rivaroxaban had no significant impact on the PK parameters of andexanet. Andexanet (up to 60 mg kg-1 day-1 ) was well tolerated in monkeys, with no accumulation of andexanet or rivaroxaban. There was a single occurrence of anaphylaxis, which resolved after treatment with diphenhydramine and epinephrine. There was no histological evidence of prothrombotic activity with high-dose andexanet compared with vehicle control, as measured by clot and fibrin deposition in all major organs. Conclusions These data suggest that andexanet is a promising therapy for the reversal of FXa inhibitor-induced anticoagulation, supporting clinical studies in humans.

The approach to the patient with an unknown overdose

Toxic overdose can present with various clinical signs and symptoms. These may be the only clues to diagnosis when the cause of toxicity is unknown at the time of initial assessment. The prognosis and clinical course of recovery of a patient poisoned by a specific agent depends largely on the quality of care delivered within the first few hours in the emergency setting. Usually the drug or toxin can be quickly identified by a careful history, a directed physical examination, and commonly available laboratory tests. Once the patient has been stabilized, the physician must consider how to minimize the bioavailability of toxin not yet absorbed, which antidotes (if any) to administer, and if other measures to enhance elimination are necessary.