Kinetic interactions between 4-methylpyrazole and ethanol in healthy humans

Fomepizole use reported to United States Poison Centers from 2010 to 2021

BACKGROUND

The diagnosis of toxic alcohol poisoning is often based on clinical presentation and nonspecific surrogate laboratory studies due to limited testing availability. Fomepizole is the recommended antidote and often administered empirically. The objective of this study is to identify substances that mimic toxic alcohols and compare key clinical factors between toxic alcohol and non-toxic alcohol exposures when fomepizole was administered.

METHODS

This study was a retrospective evaluation using the National Poison Data System from January 1, 2010 through December 31, 2021. Exposures were included if fomepizole was administered. Toxic alcohol exposures had ethylene glycol or methanol as a coded substance. For exposures not coded as a toxic alcohol, the first substance was described. Paracetamol (acetaminophen) exposures from 2020 and 2021 were excluded.

RESULTS

Fomepizole was reportedly used 25,110 times over 12 years. Use increased from 1,955 in 2010 to 2,710 in 2021. Most administrations were for reported toxic alcohol poisoning (60 percent) but use in reported non-toxic alcohol poisoning was greater starting in 2020. Toxic alcohol exposures were older (43.3 versus 39.8 years; P < 0.001) and more likely male (65.7 percent versus 58.2 percent). Level of care was mostly a critical care unit (67.7 percent), which was less common in toxic alcohol (63.3 percent) than non-toxic alcohol exposures (74.2 percent). The most common non-toxic alcohol substances were ethanol (24.9 percent) or an unknown drug (17.5 percent). Acidosis, increased creatinine concentration, anion gap, and osmolal gap, and kidney failure were coded in a lower proportion of toxic alcohol exposures than non-toxic alcohol exposures (P < 0.001).

DISCUSSION

The inability to provide rapid clinical confirmation of toxic alcohol poisoning results in the empiric administration of fomepizole to many patients who will ultimately have other diagnoses. Although fomepizole is relative well tolerated we estimated that this practice costs between $1.5 to $2.5 million. The major limitations of this work include the biases associated with retrospective record review, and the inability to confirm the exposures which may have resulted in allocation error.

CONCLUSION

Most fomepizole use was for a presumed toxic alcohol. This recently shifted to greater use in likely non-toxic alcohol poisoning. Key difference between the groups suggest fomepizole administration was likely due to the difficulty in diagnosis of toxic alcohol poisoning along with the efficacy and safety of fomepizole. Increased toxic alcohol laboratory testing availability could improve timely diagnosis, reserving fomepizole use for toxic alcohol poisoning.

Analysis of Fomepizole Elimination in Methanol- and Ethylene Glycol-Poisoned Patients

INTRODUCTION

Fomepizole is an anti-metabolite therapy that is used to diminish the toxicity from methanol or ethylene glycol. Although its elimination kinetics have been well described in healthy human subjects, the elimination in poisoned patients have only been described in a few isolated cases. This study was designed to relate the elimination of fomepizole in a series of poisoned patients to that in healthy humans.

METHODS

Plasma samples from 26 patients in the clinical trials of the use of fomepizole for methanol and ethylene glycol poisoning were analyzed for fomepizole concentrations. The elimination of fomepizole was assessed after individual doses, both during and without intermittent hemodialysis.

RESULTS

In methanol- and ethylene glycol-poisoned patients, fomepizole had a volume of distribution of 0.66-0.68 L/kg. After repeated doses of fomepizole, the minimum trough concentration averaged 86-109 µmol/L, which is 10 times higher than the minimum therapeutic concentration. In healthy human subjects, fomepizole elimination follows Michaelis-Menten kinetics and has been calculated as zero-order elimination rates. Zero-order elimination rates averaged 13 and 17 μmol/L/h in methanol and ethylene glycol patients, respectively, compared to 6-19 μmol/L/h in healthy subjects. Elimination during intermittent hemodialysis followed first-order kinetics, with a half-life of 3 h.

CONCLUSIONS

Plasma concentrations during the repeated dosing confirmed that the recommended dosing schedule, with and without intermittent hemodialysis, maintained therapeutic concentrations throughout the treatments. Fomepizole elimination in poisoned patients at therapeutic plasma concentrations appears be similar to that reported previously in healthy human subjects.

Fomepizole to treat disulfiram-ethanol reaction: a case series

Introduction: Disulfiram-ethanol reaction (DER) due to acetaldehyde accumulation occurs after drinking ethanol during disulfiram therapy. DER may result in life-threatening toxicity requiring urgent critical care. Fomepizole, an alcohol dehydrogenase inhibitor used to treat toxic alcohol poisoning, has been suggested for treating DER by preventing the metabolism of ethanol to acetaldehyde. However, its effectiveness and safety have been poorly assessed in this setting.Cases: Ten DER patients (median age, 40 years; 7 males/3 females) were included in the study. DER features consisted of consciousness impairment (median Glasgow coma score, 13; need for mechanical ventilation, 30%) with flushing (50%), vomiting (40%), electrocardiogram abnormalities (30%) and circulatory failure requiring norepinephrine (30%). Patients were successfully treated with a single intravenous infusion of fomepizole (median dose, 7.5 mg/kg). The three patients receiving norepinephrine did not improve until fomepizole was administered. The other seven patients improved promptly following fomepizole infusion without requirement for vasopressor support. All patients fully recovered. Local pain at the injection site was the only reported adverse reaction in one patient.Conclusion: Our case series supports the effectiveness and safety of fomepizole in rapidly reversing DER-induced vasodilatation and toxicity.

Analysis of fomepizole safety based on a 16-year post-marketing experience in France

Introduction: Fomepizole has been recommended as first-line antidote to treat ethylene glycol and methanol poisoning. Despite more than 30 years of utilization, the safety of fomepizole when used clinically has not been well documented. Based on the long-standing clinical experience with fomepizole in France, we investigated its safety profile in patients treated for suspected toxic alcohol poisoning.Methods: We designed a 16-year post-marketing study to evaluate the indications for fomepizole prescriptions and to investigate its safety. Data were retrospectively collected using a standardized questionnaire sent each month by post to each French hospital that ordered fomepizole during the month before. The response rate to our survey was 59%.Results: Five hundred and thirty-six patients [188 females/348 males; age, 46 years [34-55] (median [25th-75th percentiles])] were treated with fomepizole [cumulative dose, 18.6 mg/kg [15.5-26.3] (1,268 mg [900-2,100])]. Ethylene glycol/methanol poisoning was confirmed in 275 patients (51%) while a nontoxic exposure was diagnosed in 147 patients (27%). Toxic alcohol poisoning was misdiagnosed in the remaining 114 patients (21%), before the assessment of an alternative poisoning or non-poisoning diagnosis. Fifty adverse reactions were attributed to fomepizole in 36 patients (7%) including general reactions (N = 22), local reactions (N = 22) and laboratory test impairments (N = 6). All were considered mild and transient. None required stopping fomepizole. The most frequent adverse effects were injection site pain/burning (N = 13), nausea/vomiting (N = 8), vessel puncture site inflammation (N = 7), drowsiness/confusion (N = 5) and serum aminotransferase elevation (N = 3). None of the fatalities (N = 37, 7%) or persistent symptoms on discharge (N = 9; 2%) was related to fomepizole.Conclusion: Our longitudinal cohort study supports the safety of fomepizole administered to treat presumed EG and methanol poisoning.

Pharmacokinetic and pharmacodynamic drug interactions with ethanol (alcohol)

Ethanol (alcohol) is one of the most widely used legal drugs in the world. Ethanol is metabolized by alcohol dehydrogenase (ADH) and the cytochrome P450 (CYP) 2E1 drug-metabolizing enzyme that is also responsible for the biotransformation of xenobiotics and fatty acids. Drugs that inhibit ADH or CYP2E1 are the most likely theoretical compounds that would lead to a clinically significant pharmacokinetic interaction with ethanol, which include only a limited number of drugs. Acute ethanol primarily alters the pharmacokinetics of other drugs by changing the rate and extent of absorption, with more limited effects on clearance. Both acute and chronic ethanol use can cause transient changes to many physiologic responses in different organ systems such as hypotension and impairment of motor and cognitive functions, resulting in both pharmacokinetic and pharmacodynamic interactions. Evaluating drug interactions with long-term use of ethanol is uniquely challenging. Specifically, it is difficult to distinguish between the effects of long-term ethanol use on liver pathology and chronic malnutrition. Ethanol-induced liver disease results in decreased activity of hepatic metabolic enzymes and changes in protein binding. Clinical studies that include patients with chronic alcohol use may be evaluating the effects of mild cirrhosis on liver metabolism, and not just ethanol itself. The definition of chronic alcohol use is very inconsistent, which greatly affects the quality of the data and clinical application of the results. Our study of the literature has shown that a significantly higher volume of clinical studies have focused on the pharmacokinetic interactions of ethanol and other drugs. The data on pharmacodynamic interactions are more limited and future research addressing pharmacodynamic interactions with ethanol, especially regarding the non-central nervous system effects, is much needed.

Metabolic methanol: molecular pathways and physiological roles

Methanol has been historically considered an exogenous product that leads only to pathological changes in the human body when consumed. However, in normal, healthy individuals, methanol and its short-lived oxidized product, formaldehyde, are naturally occurring compounds whose functions and origins have received limited attention. There are several sources of human physiological methanol. Fruits, vegetables, and alcoholic beverages are likely the main sources of exogenous methanol in the healthy human body. Metabolic methanol may occur as a result of fermentation by gut bacteria and metabolic processes involving S-adenosyl methionine. Regardless of its source, low levels of methanol in the body are maintained by physiological and metabolic clearance mechanisms. Although human blood contains small amounts of methanol and formaldehyde, the content of these molecules increases sharply after receiving even methanol-free ethanol, indicating an endogenous source of the metabolic methanol present at low levels in the blood regulated by a cluster of genes. Recent studies of the pathogenesis of neurological disorders indicate metabolic formaldehyde as a putative causative agent. The detection of increased formaldehyde content in the blood of both neurological patients and the elderly indicates the important role of genetic and biochemical mechanisms of maintaining low levels of methanol and formaldehyde.

Dietary methanol regulates human gene activity

Methanol (MeOH) is considered to be a poison in humans because of the alcohol dehydrogenase (ADH)-mediated conversion of MeOH to formaldehyde (FA), which is toxic. Our recent genome-wide analysis of the mouse brain demonstrated that an increase in endogenous MeOH after ADH inhibition led to a significant increase in the plasma MeOH concentration and a modification of mRNA synthesis. These findings suggest endogenous MeOH involvement in homeostasis regulation by controlling mRNA levels. Here, we demonstrate directly that study volunteers displayed increasing concentrations of MeOH and FA in their blood plasma when consuming citrus pectin, ethanol and red wine. A microarray analysis of white blood cells (WBC) from volunteers after pectin intake showed various responses for 30 significantly differentially regulated mRNAs, most of which were somehow involved in the pathogenesis of Alzheimer's disease (AD). There was also a decreased synthesis of hemoglobin mRNA, HBA and HBB, the presence of which in WBC RNA was not a result of red blood cells contamination because erythrocyte-specific marker genes were not significantly expressed. A qRT-PCR analysis of volunteer WBCs after pectin and red wine intake confirmed the complicated relationship between the plasma MeOH content and the mRNA accumulation of both genes that were previously identified, namely, GAPDH and SNX27, and genes revealed in this study, including MME, SORL1, DDIT4, HBA and HBB. We hypothesized that human plasma MeOH has an impact on the WBC mRNA levels of genes involved in cell signaling.

Effect of 4-methylpyrazole on antioxidant enzyme status and lipid peroxidation in the liver of rats after exposure to ethylene glycol and ethyl alcohol

BACKGROUND

The aim of the conducted studies was to evaluate the effect of 4-methylpyrazole, increasingly used in detoxifying treatments after ethylene glycol poisoning, on the activity of some antioxidant enzymes and lipid peroxidation formation in the liver of rats after experimental co-exposure to ethylene glycol and ethyl alcohol.

METHODS

The trials were conducted on adult male Wistar rats. Ethylene glycol (EG) at the dose of 3.83 g/kg bw and ethyl alcohol (EA) at the dose of 1 g/kg bw were administered po, and 4-methylpyrazole (4-MP) at the dose of 0.01 g/kg bw was administered ip. Parameters of antioxidant balance were evaluated in hepatic cytosol, including the activity of the following enzymes: glutathione S-transferase (GST), glutathione reductase (GR), glutathione peroxidase (GPx) and lipid peroxidation level (TBARS).

RESULTS

The results suggest that evaluation of the effects of administrated 4-MP after co-exposure to EG and EA in the liver revealed statistically significant changes on antioxidant enzyme system and malondialdehyde formation.

CONCLUSION

The changes in biomarkers activity indicate a greater production of free radicals which exceeds the capability of antioxidant system, appearing with oxidative stress in the group of animals treated by 4-MP combined with EG and EA.

Treatment of patients with ethylene glycol or methanol poisoning: focus on fomepizole

Ethylene glycol (EG) and methanol are responsible for life-threatening poisonings. Fomepizole, a potent alcohol dehydrogenase (ADH) inhibitor, is an efficient and safe antidote that prevents or reduces toxic EG and methanol metabolism. Although no study has compared its efficacy with ethanol, fomepizole is recommended as a first-line antidote. Treatment should be started as soon as possible, based on history and initial findings including anion gap metabolic acidosis, while awaiting measurement of alcohol concentration. Administration is easy (15 mg/kg-loading dose, either intravenously or orally, independent of alcohol concentration, followed by intermittent 10 mg/kg-doses every 12 hours until alcohol concentrations are <30 mg/dL). There is no need to monitor fomepizole concentrations. Administered early, fomepizole prevents EG-related renal failure and methanol-related visual and neurological injuries. When administered prior to the onset of significant acidosis or organ injury, fomepizole may obviate the need for hemodialysis. When dialysis is indicated, 1 mg/kg/h-continuous infusion should be provided to compensate for its elimination. Side-effects are rarely serious and with a lower occurrence than ethanol. Fomepizole is contraindicated in case of allergy to pyrazoles. It is both efficacious and safe in the pediatric population, but is not recommended during pregnancy. In conclusion, fomepizole is an effective and safe first-line antidote for EG and methanol intoxications.

Fomepizole: a critical assessment of current dosing recommendations

Fomepizole, 4-methylpyrazole (4-MP), is a competitive antagonist of alcohol dehydrogenase with a binding affinity >8000 times that of ethanol. The drug is currently labeled by the United States Food and Drug Administration for the treatment of adult patients with known or suspected ethylene glycol or methanol poisoning. Fomepizole's wide therapeutic dose range and safety profile confer several advantages over standard ethanol therapy for the treatment of toxic alcohol exposures, including the lack of ethanol-associated side effects. Published data and data obtained from the drug's manufacturer implies that the dose escalation after 48 hours is to compensate for fomepizole-induced increased body clearance resulting from autoinduction of the cytochrome P450 (CYP) drug metabolizing enzyme CYP2E1. However, we were unable to identify any evidence of fomepizole's metabolism occurring via CYP2E1 in humans while the data most frequently cited as evidence for induction do not appear to support this claim. Based on this data along with the apparent zero-order kinetics, the current dose increase recommendations may be unnecessary and considering the safety margin described for fomepizole, an extremely conservative constant higher dose administered every 12 hours would appear to assure efficacy and tolerability. Despite the evidence, dose changes should only be implemented after careful clinical trials.

Increased Plasma Fatty Acid Ethyl Ester Levels Following Inhibition of Oxidative Metabolism of Ethanol by 4-Methylpyrazole Treatment in Human Subjects

BACKGROUND

Recent experimental evidence suggests that fatty acid ethyl esters (FAEE), nonoxidative metabolites of ethanol, mediate ethanol-induced organ damage. A direct association between pancreas-specific toxicity and increased levels of FAEE following inhibition of the oxidative metabolism of ethanol by 4-methylpyrazole (4-MP) has previously been shown in studies with rats.

METHODS

We obtained plasma samples from 32 healthy human volunteers who drank ethanol following 4-MP or placebo ingestion to determine whether in vivo inhibition of oxidative metabolism of ethanol causes a shift to nonoxidative metabolism of ethanol and the subsequent production of increased levels of FAEE. Plasma FAEE were isolated by solid-phase extraction and quantified by gas chromatography-mass spectrometry (GC-MS).

RESULTS

Plasma FAEE levels in subjects receiving 4-MP treatment before ethanol consumption were elevated compared with plasma FAEE concentrations taken from control subjects who received a placebo before ethanol ingestion. Increased FAEE levels in the 4-MP treatment group occurred after peak blood ethanol, and peak FAEE levels were achieved. There was a correlation between the blood ethanol and the plasma FAEE levels, and the correlation persisted in the presence or absence of 4-MP. The peak FAEE values were greater in men than in women, with or without 4-MP treatment.

CONCLUSIONS

Our results indicate that the in vivo inhibition of the oxidative metabolism of ethanol using 4-MP results in an increased circulating concentration of FAEE, products of the nonoxidative metabolism of ethanol.

Current recommendations for treatment of severe toxic alcohol poisonings

BACKGROUND

Ethylene glycol (EG) and methanol are responsible for accidental, suicidal, and epidemic poisonings, resulting in death or permanent sequelae. Toxicity is due to the metabolic products of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase. Conventional management of these intoxications consists of ethanol and hemodialysis. Fomepizole, a potent ADH inhibitor, has largely replaced antidotal ethanol use in France and two recent prospective U.S. trials definitively established its efficacy. Fomepizole appears safer than ethanol and while no comparative study of efficacy exists, fomepizole is recommended as the first-line antidote.

FOCUS

Fomepizole, administered early in EG intoxication, prevents renal injury. In the absence of renal failure, EG clearance is rapid, avoiding the need for prolonged fomepizole administration. The long elimination half-life of methanol poisonings, with absent hemodialysis, necessitates prolonged administration of fomepizole. In the U.S. trials, patients were dialyzed when plasma EG or methanol concentrations were >/=0.5 g/l. However, EG-poisoned patients treated with fomepizole prior to the onset of significant acidosis may not require hemodialysis. Indeed, fomepizole may also obviate the need for hemodialysis in selected methanol-poisoned patients, in the absence of neurological and ocular impairment or severe acidosis. When dialysis is indicated, 1 mg.kg.h continuous infusion of fomepizole should be provided to compensate for its elimination.

CONCLUSIONS

Fomepizole is an effective and safe first-line recommended antidote for EG and methanol intoxication. In selected patients, fomepizole may obviate the need for hemodialysis.

The influence of L-carnitine on methanol biotransformation in rats

There persists a need for potent and safe inhibitors of alcohol dehydrogenase (ADH), to effectively treat methanol poisoning by slowing its rate of biotransformation to there toxic products, formaldehyde and formic acid. Only a few former papers have reported on the significant effectiveness of L-carnitine in treating ethanol poisoning as well as alcohol abuse. As are no reports on the effectiveness of L-carnitine in treating methanol poisoning till now, the current studies were conducted to investigate the influence of L-carnitine on both oxydative metabolism and elimination of methanol in rats. Male Sprague-Dawley rats, aged 3 months with the body weight of 200-230 g were divided into 6 groups at random, with two of the groups considered to be control. Rats were given drinking water (control) or methanol in two different doses of 3220 mg/kg b.m. or 6440 mg/kg b.m. intragastrically and 0.9% NaCl (control) or 6.2 mmol/kg b.m. of L-carnitine intraperitionelly. Within 96 hours after the administration of methanol and 0.9% NaCl or L-carnitine, the urine was collected and then the animals were decapitated. To determine methanol there were taken blood samples for clot, and to determine carnitine and its derivatives blood was taken into heparinized test tubes. During the autopsy liver was also secured. In all the experimental time points stated the methanol concentrations in blood, urine and liver homogenate were determined by a head-space gas chromatography.

Testosterone increases in men after a low dose of alcohol

BACKGROUND

Heavy acute alcohol drinking decreases blood testosterone in men due to an effect on the testicular level. An acute increase in blood testosterone levels after a low alcohol dose has, however, recently been reported in women. The objective of this investigation was to study the effect of a low alcohol dose on testosterone in men and further elucidate the mechanism behind the effect by using 4-methylpyrazole, an inhibitor of alcohol metabolism.

METHODS

A double-blind placebo-controlled interventional crossover trial in random order (n = 13).

RESULTS

After intake of alcohol (0.5 g/kg, 10% w/v), an acute increase in plasma testosterone (from 13.5 +/- 1.2 nmol/liter to 16.0 +/- 1.6 nmol/liter, mean +/- SEM; p < 0.05), a decrease in androstenedione (from 5.1 +/- 0.4 nmol/liter to 4.0 +/- 0.3 nmol/liter; p < 0.05), and an increase in the testosterone:androstenedione ratio (from 2.8 +/- 0.3 to 4.2 +/- 0.4; p < 0.01) were observed. The effects were not observed during pretreatment with 4-methylpyrazole (10-15 mg/kg orally), which inhibited the ethanol elimination rate by 37 +/- 3%.

CONCLUSIONS

Alcohol intake affects the androgen balance in men through an effect mediated by the alcohol-induced change in the redox state in the liver.

American Academy of Clinical Toxicology practice guidelines on the treatment of methanol poisoning

EPIDEMIOLOGY

Almost all cases of acute methanol toxicity result from ingestion, though rarely cases of poisoning have followed inhalation or dermal absorption. The absorption of methanol following oral administration is rapid and peak methanol concentrations occur within 30-60minutes.

MECHANISMS OF TOXICITY

Methanol has a relatively low toxicity and metabolism is responsible for the transformation of methanol to its toxic metabolites. Methanol is oxidized by alcohol dehydrogenase to formaldehyde. The oxidation of formaldehyde to formic acid is facilitated by formaldehyde dehydrogenase. Formic acid is converted by 10-formyl tetrahydrofolate synthetase to carbon dioxide and water. In cases of methanol poisoning, formic acid accumulates and there is a direct correlation between the formic acid concentration and increased morbidity and mortality. The acidosis observed in methanol poisoning appears to be caused directly or indirectly by formic acid production. Formic acid has also been shown to inhibit cytochrome oxidase and is the prime cause of ocular toxicity, though acidosis can increase toxicity further by enabling greater diffusion of formic acid into cells.

FEATURES

Methanol poisoning typically induces nausea, vomiting, abdominal pain, and mild central nervous system depression. There is then a latent period lasting approximately 12-24 hours, depending, in part, on the methanol dose ingested, following which an uncompensated metabolic acidosis develops and visualfunction becomes impaired, ranging from blurred vision and altered visual fields to complete blindness.

MANAGEMENT

For the patient presenting with ophthalmologic abnormalities or significant acidosis, the acidosis should be corrected with intravenous sodium bicarbonate, the further generation of toxic metabolite should be blocked by the administration of fomepizole or ethanol and formic acid metabolism should be enhanced by the administration of intravenous folinic acid. Hemodialysis may also be required to correct severe metabolic abnormalities and to enhance methanol and formate elimination. For the methanol poisoned patient without evidence of clinical toxicity, the first priority is to inhibit methanol metabolism with intravenous ethanol orfomepizole. Although there are no clinical outcome data confirming the superiority of either of these antidotes over the other, there are significant disadvantages associated with ethanol. These include complex dosing, difficulties with maintaining therapeutic concentrations, the need for more comprehensive clinical and laboratory monitoring, and more adverse effects. Thus fomepizole is very attractive, however, it has a relatively high acquisition cost.

CONCLUSION

The management of methanol poisoning includes standard supportive care, the correction of metabolic acidosis, the administration of folinic acid, the provision of an antidote to inhibit the metabolism of methanol to formate, and selective hemodialysis to correct severe metabolic abnormalities and to enhance methanol and formate elimination. Although both ethanol and fomepizole are effective, fomepizole is the preferred antidote for methanol poisoning.

Diagnosis and treatment of an unusual cause of metabolic acidosis: ethylene glycol poisoning

Ethylene glycol intoxication is a rare but dangerous type of poisoning. It causes a severe acidosis with high anion and osmolal gaps. Clinical manifestations of the ethylene glycol intoxication can be divided in three phases: a neurologic stage, with hallucinations, stupor and coma; the second stage is cardiovascular with cardiac failure. Renal failure characterizes the third stage, due to acute tubular necrosis. After aggressive gastric emptying, the main treatment is ethanol or 4-methypyrazole, which can be given either orally or intravenous, with supportive measures for all symptoms or diseased organ.

American Academy of Clinical Toxicology Practice Guidelines on the Treatment of Ethylene Glycol Poisoning. Ad Hoc Committee

Fomepizole (4-methylpyrazole, 4-MP, Antizol) is a potent inhibitor of alcohol dehydrogenase that was approved recently by the US Food and Drug Administration (FDA) for the treatment of ethylene glycol poisoning. Although ethanol is the traditional antidote for ethylene glycol poisoning, it has not been studied prospectively. Furthermore, the FDA has not approved the use of ethanol for this purpose. Case reports and a prospective case series indicate that the intravenous (i.v.) administration of fomepizole every 12 hours prevents renal damage and metabolic abnormalities associated with the conversion of ethylene glycol to toxic metabolites. Currently, there are insufficient data to define the relative role of fomepizole and ethanol in the treatment of ethylene glycol poisoning. Fomepizole has clear advantages over ethanol in terms of validated efficacy, predictable pharmacokinetics, ease of administration, and lack of adverse effects, whereas ethanol has clear advantages over fomepizole in terms of long-term clinical experience and acquisition cost. The overall comparative cost of medical treatment using each antidote requires further study.

Toxicokinetics of organic solvents: a review of modifying factors

This article reviews, with an emphasis on human experimental data, factors known or suspected to cause changes in the toxicokinetics of organic solvents. Such changes in the toxicokinetic pattern alters the relation between external exposure and target dose and thus may explain some of the observed individual variability in susceptibility to toxic effects. Factors shown to modify the uptake, distribution, biotransformation, or excretion of solvent include physical activity (work load), body composition, age, sex, genetic polymorphism of the biotransformation, ethnicity, diet, smoking, drug treatment, and coexposure to ethanol and other solvents. A better understanding of modifying factors is needed for several reasons. First, it may help in identifying important potential confounders and eliminating negligible ones. Second, the risk assessment process may be improved if different sources of variability between external exposures and target doses can be quantitatively assessed. Third, biological exposure monitoring may be also improved for the same reason.

Treatment of methanol poisoning with intravenous 4-methylpyrazole

Treatment of human methanol poisoning with the alcohol dehydrogenase inhibitor, 4-methylpyrazole (fomepizole), has not been previously described. We report the clinical and toxicokinetic data of a patient with methanol poisoning who was treated with fomepizole. Formic acid levels remained undetectable during fomepizole treatment, the toxic effects of methanol were prevented, and the patient made a full recovery.