4-Methylpyrazole: a controlled study of safety in healthy human subjects after single, ascending doses

Methanol poisoning outbreak in Saudi Arabia: a case series

Background

Outbreaks of methanol poisoning have been described in the medical literature in different regions around the world. Even though in Saudi Arabia a few outbreaks of methanol poisoning have occurred, they remain undocumented. Herein, we describe several cases of methanol poisoning in Saudi Arabia with the goal of increasing awareness about the dangers of methanol poisoning among healthcare staff.

Case presentation

Nine middle-aged Saudi patients (five men aged 24, 26, 27, 36, and 49 years and four females aged 19, 20, 24, and 25 years) were admitted to our emergency department after alcohol consumption. All patients presented with severe metabolic acidosis and some visual impairment. Treatment was initiated based on the clinical suspicion of methanol intoxication because of laboratory test limitations and time constraints. Patients showed improvement and favorable hospital outcomes after aggressive empirical treatment.

Conclusions

Many social and cultural factors influence the lack of reporting of methanol poisoning cases in Saudi Arabia. We believe it is important to document these outbreaks to increase the knowledge among healthcare providers and promote public health awareness. A high index of suspicion and the development of local public health networks to monitor, survey, follow-up, and facilitate data exchange can help healthcare providers recognize and aggressively treat affected individuals. Early empiric and aggressive management can greatly decrease morbidity and mortality despite challenges and limited resources.

Comparing N-acetylcysteine and 4-methylpyrazole as antidotes for acetaminophen overdose

Acetaminophen (APAP) overdose can cause hepatotoxicity and even liver failure. N-acetylcysteine (NAC) is still the only FDA-approved antidote against APAP overdose 40 years after its introduction. The standard oral or intravenous dosing regimen of NAC is highly effective for patients with moderate overdoses who present within 8 h of APAP ingestion. However, for late-presenting patients or after ingestion of very large overdoses, the efficacy of NAC is diminished. Thus, additional antidotes with an extended therapeutic window may be needed for these patients. Fomepizole (4-methylpyrazole), a clinically approved antidote against methanol and ethylene glycol poisoning, recently emerged as a promising candidate. In animal studies, fomepizole effectively prevented APAP-induced liver injury by inhibiting Cyp2E1 when treated early, and by inhibiting c-jun N-terminal kinase (JNK) and oxidant stress when treated after the metabolism phase. In addition, fomepizole treatment, unlike NAC, prevented APAP-induced kidney damage and promoted hepatic regeneration in mice. These mechanisms of protection (inhibition of Cyp2E1 and JNK) and an extended efficacy compared to NAC could be verified in primary human hepatocytes. Furthermore, the formation of oxidative metabolites was eliminated in healthy volunteers using the established treatment protocol for fomepizole in toxic alcohol and ethylene glycol poisoning. These mechanistic findings, together with the excellent safety profile after methanol and ethylene glycol poisoning and after an APAP overdose, suggest that fomepizole may be a promising antidote against APAP overdose that could be useful as adjunct treatment to NAC. Clinical trials to support this hypothesis are warranted.

Use of fomepizole (4-methylpyrazole) for acetaminophen poisoning: A scoping review

INTRODUCTION

Acetaminophen (paracetamol, APAP) poisoning is a prominent global cause of drug-induced liver injury. While N-acetylcysteine (NAC) is an effective antidote, it has therapeutic limitations in massive overdose or delayed presentation. The objective is to comprehensively review the literature on fomepizole as a potential adjunct antidote for acetaminophen toxicity.

METHODS

A scoping review was performed using standardized search terms from inception through July 2021.

RESULTS

Reports on fomepizole as a therapeutic adjunct for APAP toxicity span heterogeneous types of evidence. Eleven preclinical studies (in vitro and animal), fourteen case reports/series, and one human volunteer study were included. Fomepizole's action is mediated by inhibition of CYP2E1 to prevent oxidant stress generation, and inhibition of c-Jun N-terminal kinase (JNK) to decrease amplification of oxidant stress signaling to mitochondria. Studies have shown a reduction in oxidative metabolites likely by shunting metabolism away from CYP2E1 and a resultant decrease in liver injury in animals, independent of CYP2E1 interactions. Fomepizole has been linked to few adverse effects.

CONCLUSION

Based on in vitro and animal studies, and bolstered by case reports, fomepizole likely offers benefit as an adjunct antidote for APAP toxicity, however this remains to be shown in a human trial. NAC remains the standard of care antidote, but given that fomepizole is approved and generally safe, it may be considered for APAP toxicity as off-label use by experienced clinicians, in rare circumstances associated with increased risk of hepatotoxicity despite standard NAC dosing. The marginal clinical benefit of fomepizole adjunct therapy beyond NAC monotherapy remains to be clearly defined, and routine use for APAP overdose is premature based on current evidence.

Novel Therapeutic Approaches Against Acetaminophen-induced Liver Injury and Acute Liver Failure

Liver injury and acute liver failure caused by acetaminophen (APAP, N-acetyl-p-aminophenol, paracetamol) overdose is a significant clinical problem in most western countries. The only clinically approved antidote is N-acetylcysteine (NAC), which promotes the recovery of hepatic GSH. If administered during the metabolism phase, GSH scavenges the reactive metabolite N-acetyl-p-benzoquinone imine. More recently, it was shown that NAC can also reconstitute mitochondrial GSH levels and scavenge reactive oxygen/peroxynitrite and can support mitochondrial bioenergetics. However, NAC has side effects and may not be efficacious after high overdoses. Repurposing of additional drugs based on their alternate mechanisms of action could be a promising approach. 4-Methylpyrazole (4MP) was shown to be highly effective against APAP toxicity by inhibiting cytochrome P450 enzymes in mice and humans. In addition, 4MP is a potent c-Jun N-terminal kinase inhibitor expanding its therapeutic window. Calmangafodipir (CMFP) is a SOD mimetic, which is well tolerated in patients and has the potential to be effective after severe overdoses. Other drugs approved for humans such as metformin and methylene blue were shown to be protective in mice at high doses or at human therapeutic doses, respectively. Additional protective strategies such as enhancing antioxidant activities, Nrf2-dependent gene induction and autophagy activation by herbal medicine components are being evaluated. However, at this point, their mechanistic insight is limited, and the doses used are high. More rigorous mechanistic studies are needed to advance these herbal compounds. Nevertheless, based on recent studies, 4-methylpyrazole and calmangafodipir have realistic prospects to become complimentary or even alternative antidotes to NAC for APAP overdose.

Solvent-based paint and varnish removers: a focused toxicologic review of existing and alternative constituents

Paint and varnish removers constitute a major potential source of organic solvent exposure to contractors and home improvement enthusiasts. Unfortunately, the leading paint remover formulations have traditionally contained, as major ingredients, chemicals classified as probable human carcinogens (eg, methylene chloride) or reproductive toxicants (eg, N-methylpyrrolidone). In addition, because of its unique toxicology (ie, hepatic conversion to carbon monoxide compounding generic solvent narcosis and arrythmogenesis), high volatility, and rigorous requirements for personal protective equipment, methylene chloride exposures from paint removers have been linked to numerous deaths involving both occupational and consumer usage. The aim of this review is to summarize the known toxicology of solvent-based paint remover constituents (including those found in substitute formulations) in order to provide health risk information to regulators, chemical formulators, and end-users of this class of products, and to highlight any data gaps that may exist.

Butanediol Conversion to Gamma-Hydroxybutyrate Markedly Reduced by the Alcohol Dehydrogenase Blocker Fomepizole

1,4-Butanediol (BDO)-used as solvent and abused for its euphoric effects-is converted to gamma-hydroxybutyrate (GHB) by the enzyme alcohol dehydrogenase. This double-blind, placebo-controlled crossover study with six healthy volunteers is the first to date investigating the role of the ADH inhibitor fomepizole (4-methylpyrazole (4MP)) in moderating this conversion in humans. Participants received on two different days either intravenous placebo or 15 mg/kg 4MP followed by oral administration of 25 mg/kg BDO. Pretreatment with 4MP resulted in significantly higher BDO maximal plasma concentration (P = 0.001) and area under the concentration-time curve (AUC; P = 0.028), confirming that ADH is the primary pathway for the conversion of BDO to GHB in humans. With 4MP, the mean arterial pressure was significantly lower at 105 minutes compared to baseline (P = 0.003), indicating that blood pressure lowering, observed not with a temporal relationship to 4MP administration but after the maximum BDO concentration was reached, may be an intrinsic effect of BDO.

Antidote Use in the Critically Ill Poisoned Patient

The proper use of antidotes in the intensive care setting when combined with appropriate general supportive care may reduce the morbidity and mortality associated with severe poisonings. The more commonly used antidotes that may be encountered in the intensive care unit ( N-acetylcysteine, ethanol, fomepizole, physostigmine, naloxone, flumazenil, sodium bicarbonate, octreotide, pyridoxine, cyanide antidote kit, pralidoxime, atropine, digoxin immune Fab, glucagon, calcium gluconate and chloride, deferoxamine, phytonadione, botulism antitoxin, methylene blue, and Crotaline snake antivenom) are reviewed. Proper indications for their use and knowledge of the possible adverse effects accompanying antidotal therapy will allow the physician to appropriately manage the severely poisoned patient.

Studies on ethylene glycol poisoning: one patient - 154 admissions

OBJECTIVE

Fomepizole is the antidote of choice in toxic alcohol poisonings. Potential side effects from frequent use of fomepizole were studied in a patient admitted 154 times with ethylene glycol (EG) poisoning. The intra-individual correlation between the serum-ethylene glycol (serum-EG) and the osmolal gap (OG) EG-kinetics, and other laboratory parameters were also studied.

METHODS

Combined pro- and retrospective collection of material from three different hospitals, and results from autopsy.

RESULTS

A 26-year-old female with a dissociative disorder was admitted with EG poisoning a total of 154 times. Her admission data revealed a median pH of 7.31 (range 6.87-7.49), pCO(2): 4.2 kPa (1.2-6.7) (32 mmHg [9-50]), HCO-3: 15 mmol/L (4-26) (15 mEq/L [4-26]), base deficit (BD): 10 mmol/L (- 4 to 27) (10 mEq/L [-4 to 27]), serum-creatinine 65 μmol/L (40-133) (0.74 mg/dL [0.45-1.51]), OG 81 mOsm/kgH(2)O (25-132), and serum-EG 44 mmol/L (4-112) (250 mg/dL [25-700]). She was treated with fomepizole 99 times, ethanol 60 times (with a combination of both six times), and dialysis 73 times. The correlation between serum-EG and OG was good (r(2) = 0.76). She was finally found dead outside hospital with an EG blood concentration of 81 mmol/L (506 mg/dL). An autopsy revealed calcium oxalate crystals in the kidneys, slight liver steatosis, and slight edema of the lungs.

DISCUSSION

The frequent use of fomepizole in this young patient was not associated with any detectable side effects; neither on clinical examination and lab screening, nor on the later autopsy. Regarding the sequelae from the repetitive EG-poisoning episodes, her kidney function seemed to normalize after each overdose. She was treated with buffer and antidote without hemodialysis 81 times without complications, supporting the safety of this approach in selected cases.

Fomepizole for the treatment of pediatric ethylene and diethylene glycol, butoxyethanol, and methanol poisonings

INTRODUCTION

The use and clinical efficacy of the alcohol dehydrogenase inhibitor fomepizole is well established for the treatment of ethylene glycol and methanol poisonings in adults.

METHODS

A computerized search of the U.S. National Academy of medicine and EMBase databases was undertaken to identify published cases of patients treated with fomepizole. This search strategy identified 14 published cases related to the topic of this review: 10 due to ethylene glycol poisoning, 1 due to diethylene glycol poisoning, 1 due to butoxyethanol ingestion, and 2 due to methanol poisoning. The median age of these cases was 5.5 years old. FOMEPIZOLE IN GLYCOL AND GLYCOL ETHER POISONING: For the 10 ethylene glycol poisoned patients, the median recorded values of their arterial pH was 7.27 (range 7.03-7.38), serum bicarbonate concentration was 13 mEq/L (range 2-25), and ethylene glycol concentration was 2,140 mg/L (range 130-3,840). Eight of these patients were not hemodialyzed. The eight patients who were not hemodialyzed had ethylene glycol concentrations as high as 3,500 mg/L and serum bicarbonate concentrations as low as 4 mEq/L. All 10 patients had resolution of their metabolic acidosis and recovered without sequelae. The half-times of ethylene glycol elimination ranged from 9 to 15 h during fomepizole therapy, which is faster than the 19.7 h reported in adults. The two patients who ingested diethylene glycol or butoxyethanol all recovered without sequelae. The patient who ingested the butoxyethanol had a serum bicarbonate concentration of 13 mEq/L and was not hemodialyzed. FOMEPIZOLE IN METHANOL POISONING: One of the two children who ingested methanol was hemodialyzed. Both cases had a similar degree of severity. DOES FOMEPIZOLE OBVIATE THE NEED FOR HEMODIALYSIS?: Based on the experience reviewed herein it appears that, as in adults, hemodialysis may not be necessary in most cases of pediatric ethylene glycol poisoning if treated with fomepizole. FOMEPIZOLE PHARMACOKINETICS: Plasma fomepizole concentrations were measured in three cases and were found to be therapeutic with apparent Michaelis-Menton kinetics, having a zero-order elimination rate of 0.6-1 mg/L/h at higher concentrations and a first-order elimination with an apparent elimination half-time of 3.9 h at lower concentrations. FOMEPIZOLE REGIMEN: Most cases used the current U.S.-approved regimen. ADVERSE EFFECTS OF FOMEPIZOLE: The one adverse effect reported during fomepizole therapy was transient nystagmus in a 6-year-old with a serum ethylene glycol concentration of 130 mg/L and a serum bicarbonate concentration of 2 mEq/L; it is likely that ethylene glycol itself was the cause. COMPARISON OF FOMEPIZOLE WITH ETHANOL THERAPY: Two cases were originally treated with ethanol but switched to fomepizole because of adverse effects. In both cases, the adverse reactions to ethanol resolved once fomepizole treatment was initiated.

CONCLUSIONS

The limited data available suggest that fomepizole, using the same dosage regimen as that used for adults, is efficacious and well tolerated in pediatric patients. In many cases of pediatric ethylene glycol poisoning treated with fomepizole, hemodialysis may not be necessary despite high concentrations and the presence of metabolic acidosis.

Expert opinion: fomepizole may ameliorate the need for hemodialysis in methanol poisoning

Fomepizole is now the antidote of choice in methanol poisoning. The use of fomepizole may also change the indications for hemodialysis in these patients. We have addressed this change in a review of articles on methanol poisonings. Review of the literature (through PubMed) combined with our own experiences from two recent methanol outbreaks in Estonia and Norway. The efficiency of dialysis during fomepizole treatment was reported in only a few reports. One recent study challenged the old indications, suggesting a new approach with delayed or even no hemodialysis. Methanol-poisoned patients on fomepizole treatment may be separated into two categories: 1) The critically ill patient, with severe metabolic acidosis (base deficit >15 mM) and/or visual disturbances should be given buffer, fomepizole and immediate hemodialysis: dialysis removes the toxic anion formate, and assists in correcting the metabolic acidosis, thereby also reducing formate toxicity. The removal of methanol per se is not important in this setting because fomepizole prevents further production of formic acid. 2) The stable patient, with less metabolic acidosis and no visual disturbances, should be given buffer and fomepizole. This treatment allows for the possibility to delay, or even drop, dialysis in this setting, because patients will not develop more clinical features from methanol poisoning when fomepizole and bicarbonate is given in adequate doses. Indications and triage for hemodialysis in methanol poisonings should be modified. Delayed hemodialysis or even no hemodialysis may be an option in selected cases.

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.

Bradycardia and hypotension associated with fomepizole infusion during hemodialysis

We report a case of hypotension and bradycardia associated with intravenous fomepizole infusion.

CASE REPORT

A 59-year-old man presented to hospital 10 hours after ethylene glycol ingestion with ataxia, slurred speech, metabolic acidosis, heart rate 70/min, blood pressure 160/100 mmHg. Treatment with hemodialysis and fomepizole began 7.5 hours after admission. Severe bradycardia (29/min) and hypotension (69 mmHg systolic) occurred immediately following a 30 minute intravenous infusion of the first (19 mg/kg) fomepizole dose, but rapidly corrected with 1 mg atropine. Transient bradycardia (48/min) and hypotension (89/57 mmHg) recurred immediately after the second (10 mg/kg) fomepizole dose, also given during dialysis.

DISCUSSION

Hemodialysis may cause a drop in blood pressure and heart rate; however, the close temporal relationship with fomepizole infusions, dose-related symptom intensity and recurrence with rechallenge suggest a causal relationship with fomepizole. Hemodialysis, acidosis and high initial fomepizole dose may have enhanced patient susceptibility, as a post-dialysis fomepizole dose was well tolerated.

CONCLUSION

Fomepizole may precipitate bradycardia and/or hypotension during hemodialysis. Monitor vital signs closely during and immediately after infusion.

Emergency hemodialysis in the management of intoxication

Management of intoxicated patients has many aspects in a wide spectrum, beginning with decontamination processes and basic supportive care. The most logical therapeutic approach is probably the specific antidotes, when available and/or applicable. On the other hand, many chemicals and drugs, can be removed from the body by means of hemodialysis or hemoperfusion while treating vital sign abnormalities and electrolyte and acid-base disturbances of the patient. In this paper, we describe 11 cases of intoxication, 6 with methyl alcohol, 3 with lithium, and 2 with salicylate, admitted to emergency department and treated with hemodialysis between January 1, 2002 and December 31, 2004. We review their medical charts and detailed demographic data, medical history, type of exposure, clinical and laboratory presentations, duration of hemodialysis performed, and the outcome.

Fomepizole as a therapeutic strategy in paediatric methanol poisoning. A case report and review of the literature

Methanol poisoning is not frequently observed in children; however, without treatment, serious intoxication can be complicated by visual impairment, coma, metabolic acidosis, respiratory and circulatory insufficiency and death. Treatment in a paediatric intensive care is therefore compulsory. Methanol is metabolised in the liver by alcohol dehydrogenase to the toxic metabolites formaldehyde and formic acid. Classically, ethanol is given as a competitive inhibitor in order to avoid the formation of these compounds. We report on the use of fomepizole (4-methylpyrazole),a new and potent inhibitor of alcohol dehydrogenase, in a 3-year-old boy after the intake of a toxic amount of methanol. The course was uneventful and the use of fomepizole was not accompanied by any side-effects. An overview is given of all cases of paediatric poisoning in which fomepizole was used.

CONCLUSION

Fomepizole seems to be a safe and valid alternative to ethanol in cases of paediatric methanol poisoning.

Antidote review: fomepizole for methanol poisoning

Fomepizole (Antizol) was recently approved by the US Food and Drug Administration for treatment of methanol poisoning. By inhibiting the hepatic enzyme alcohol dehydrogenase, it presents formation of toxic metabolites with far fewer consequences than traditional ethanol therapy. It appears that fomepizole will become standard therapy for methanol intoxication as it is for ethylene glycol poisoning.

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.

Role of fomepizole in the management of ethylene glycol toxicity

OBJECTIVE

To systematically review English-language articles on fomepizole administration in patients with ethylene glycol poisoning.

DATA SOURCES

MEDLINE, EMBASE, Current Contents, and PubMed. Search terms were fomepizole, 4-methylpyrazole, and ethylene glycol. The search was supplemented with a bibliographic review of all relevant articles.

STUDY SELECTION

All published reports of fomepizole administration in patients with ethylene glycol poisoning were reviewed, irrespective of study design. We identified one clinical trial and subsequent pharmacokinetic study, one case series, and 13 case reports.

RESULTS

Fomepizole has been investigated in 70 patients in open, unblinded studies. Most patients received an intravenous loading dose, with subsequent variable maintenance doses every 12 hours until plasma ethylene glycol levels became undetectable. Additional hemodialysis treatment generally was administered when patients had renal insufficiency or ethylene glycol levels above 50 mg/dl. Many patients had detectable ethanol levels either because of coadministration or as a result of adjunctive treatment at a referring center. Poorer patient outcomes, such as death and renal insufficiency, were associated with later clinical presentation time after ingestion. At therapeutic fomepizole levels (> 8.6 mg/ml), the half-life of ethylene glycol was prolonged to over 19 hours. Fomepizole appeared to be well tolerated by most patients.

CONCLUSION

Fomepizole is an effective alcohol dehydrogenase inhibitor that decreases production of ethylene glycol metabolites. Reduced mortality and morbidity are undetermined because of the small number of patients evaluated to date. Data on comparative efficacy of fomepizole versus ethanol and data on administration of fomepizole in children are limited.

Reversal of severe methanol-induced visual impairment: no evidence of retinal toxicity due to fomepizole

CASE REPORT

We report a case of methanol poisoning exhibiting complete recovery from severe visual impairment following treatment with ethanol, fomepizole, and hemodialysis. An adult male presented with central blindness after ingesting methanol. Initial visual acuity was <20/800 (finger counting at 1-2 feet) with retinal edema on fundoscopy, arterial pH 7.19, methanol 97 mg/dL (30 mmol/L), formate 14.3 mmol/L, and ethanol undetectable. The patient was treated with ethanol, then fomepizole intravenously (15, 10, then 5 mg/kg), and hemodialysis. Methanol metabolism was effectively blocked by fomepizole even after ethanol had been eliminated, and the patient recovered 20/20 vision by day 14 with normal fundoscopy. This case report confirms highly efficient inhibition of alcohol dehydrogenase by fomepizole, as well as demonstrate the safety of fomepizole in a patient already exhibiting end-organ retinal toxicity. The potential for fomepizole to inhibit retinol dehydrogenase, an isoenzyme of alcohol dehydrogenase essential to vision, did not appear to be clinically significant in this symptomatic methanol-poisoned patient.

Current management of ethylene glycol poisoning

Ethylene glycol, a common antifreeze, coolant and industrial solvent, is responsible for many instances of accidental and intentional poisoning annually. Following ingestion, ethylene glycol is first hepatically metabolised to glycoaldehyde by alcohol dehydrogenase. Glycoaldehyde is then oxidised to glycolic acid, glyoxylic acid and finally oxalic acid. While ethylene glycol itself causes intoxication, the accumulation of toxic metabolites is responsible for the potentially fatal acidosis and renal failure, which characterises ethylene glycol poisoning. Treatment of ethylene glycol poisoning consists of emergent stabilisation, correction of metabolic acidosis, inhibition of further metabolism and enhancing elimination of both unmetabolised parent compound and its metabolites. The prevention of ethylene glycol metabolism is accomplished by the use of antidotes that inhibit alcohol dehydrogenase. Historically, this has been done with intoxicating doses of ethanol. At a sufficiently high concentration, ethanol saturates alcohol dehydrogenase, preventing it from acting on ethylene glycol, thus allowing the latter to be excreted unchanged by the kidneys. However, ethanol therapy is complicated by its own inherent toxicity, and the need to carefully monitor serum ethanol concentrations and adjust the rate of administration. A recent alternative to ethanol therapy is fomepizole, or 4-methylpyrazole. Like ethanol, fomepizole inhibits alcohol dehydrogenase; however it does so without producing serious adverse effects. Unlike ethanol, fomepizole is metabolised in a predictable manner, allowing for the use of a standard, validated administration regimen. Fomepizole therapy eliminates the need for the haemodialysis that is required in selected patients who are non-acidotic and have adequate renal function.

Comparison of the therapeutic efficacy of 4-methylpyrazole and N-acetylcysteine on acetaminophen (paracetamol) hepatotoxicity in rats

Obtaining effective analgesia with a minimal erosive effect on gastric mucosal tissue has increased the consumption of acetaminophen (paracetamol), especially among the elderly. However, the hepatotoxic effects of acetaminophen have also increased. We aimed to compare the effects of 4-methylpyrazole (4-MP), N-acetylcysteine (NAC) and their combined use on the hepatotoxicity of acetaminophen in a rat model. Male Wistar Albino rats were divided into six groups. Groups 1-5 received 2,000 mg/kg acetaminophen by gavage while the control group was group 6. Group 2 animals were given NAC (loading dose 140 mg/kg followed by seven doses at 4 h intervals); group 3 received 50 mg/kg 4-MP; group 4 received 200mg/kg 4-MP; and group 5 received NAC as in group 2 plus 200 mg/kg 4-MP. Blood samples were taken for measurements of serum AST and ALT levels. The livers of the rats were removed for microscopic examination and grading of hepatic necrosis. AST and ALT levels in groups 2-5 were lower than that of group 1 (p < 0.001), although no significant difference was noted between groups 2-5 (p > 0.05). Higher levels of ALT were found in group 5 than in group 2 (p < 0.05), and higher levels of AST were found in group 5 than in group 3 (p < 0.01). Median necrosis scores were 3.36 for rats receiving acetaminophen alone (p < 0.001, compared with groups 2-6), 1.45-1.81 for groups 2-5 (p > 0.05, compared with each other), and 0.18 for control rats (p < 0.001, compared with groups 1-5). In conclusion, the administration of 4-MP and/or NAC after 4 h of administering toxic dose of acetaminophen, inhibits hepatotoxicity in rats. There was no difference between the 4-MP and NAC-treated groups as reflected by comparable levels of serum transaminases and the degree of hepatic necrosis. Combining of 4-MP and NAC offers no benefit.

Treatment of methanol and isopropanol poisoning with intravenous fomepizole

CASE REPORT

We report a case of mixed methanol and isopropanol poisoning in a patient who refused dialysis but agreed to treatment with intravenous fomepizole. The patient was asymptomatic on arrival, with initial blood methanol and isopropanol concentrations of 146 mg/dL and 39 mg/dL, respectively. Blood ethanol was undetectable. The patient was treated with fomepizole twice daily intravenously until blood methanol was undetectable. No side effects of therapy, other than transient eosinophilia, were observed. The evolution was uneventful and no metabolites of either alcohol were detected at any time during the hospitalization. The decay of plasma methanol and isopropanol under fomepizole treatment were well described by first-order kinetics. The plasma elimination half-lives of methanol and isopropanol were 47.6 hours and 27.7 hours, respectively. Fomepizole appears to have been effective in blocking the toxic metabolism of both methanol and isopropanol and was associated with a favorable outcome.

Fomepizole for the treatment of methanol poisoning

BACKGROUND

Methanol poisoning may result in metabolic acidosis, blindness, and death. The inhibition of alcohol dehydrogenase is fundamental to the treatment of methanol poisoning. We performed a multicenter study to evaluate fomepizole, an inhibitor of alcohol dehydrogenase, in the treatment of patients with methanol poisoning.

METHODS

We administered intravenous fomepizole to 11 consecutive patients who presented with methanol poisoning at a participating center. Serial clinical and laboratory studies, including measurements of plasma formic acid and fomepizole, were performed. The outcomes measured were the preservation of visual acuity, the resolution of metabolic acidosis, the inhibition of formic acid production, the achievment of therapeutic plasma concentrations of fomepizole with the dosing regimen, residual illness or disability, and death.

RESULTS

Plasma formic acid concentrations were detectable in eight patients, and these concentrations were closely correlated with the initial arterial pH values (r=0.92, P<0.001). In response to fomepizole, plasma formic acid concentrations fell and metabolic abnormalities resolved in all patients. Nine patients survived. Seven patients initially had visual abnormalities, but at the end of the trial no surviving patient had any detectable visual deficits related to methanol poisoning. Fomepizole had few adverse effects. The two patients who died had anoxic brain injury that was present at the time of enrollment. During treatment, methanol had an elimination half-life of 54 hours.

CONCLUSIONS

Fomepizole appears to be safe and effective in the treatment of methanol poisoning.

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.

Novel therapies for ethylene glycol intoxication

Ethylene glycol is a serious toxin that children frequently ingest. Diagnosis and treatment of this poisoning are challenging and frequently involve the use of novel therapies. In the past year, fomepizole (4-methylpyrazole) has been approved for use as an antidote in the treatment of ethylene glycol poisoning in adults, and the first article reporting the use of fomepizole in a pediatric ethylene glycol exposure was published. As a result, the therapy of ethylene glycol poisoning in children is likely to change from the traditional approach of ethanol administration coupled with hemodialysis to the administration of fomepizole with or without hemodialysis.

Fomepizole for the treatment of ethylene glycol poisoning. Methylpyrazole for Toxic Alcohols Study Group

BACKGROUND

Ethylene glycol poisoning causes metabolic acidosis and renal failure and may cause death. The standard treatment is inhibition of alcohol dehydrogenase with ethanol, given in intoxicating doses, and adjunctive hemodialysis. We studied the efficacy of fomepizole, a new inhibitor of alcohol dehydrogenase, in the treatment of ethylene glycol poisoning.

METHODS

We administered intravenous fomepizole to 19 patients with ethylene glycol poisoning (plasma ethylene glycol concentration, > or =20 mg per deciliter [3.2 mmol per liter]). Patients who met specific criteria also underwent hemodialysis. Treatment was continued until plasma ethylene glycol concentrations were less than 20 mg per deciliter. Acid-base status, renal function, the kinetics of fomepizole, and ethylene glycol metabolism were assessed at predetermined intervals.

RESULTS

Fifteen of the patients initially had acidosis (mean serum bicarbonate concentration, 12.9 mmol per liter). Acid-base status tended to normalize within hours after the initiation of treatment with fomepizole. One patient with extreme acidosis died. In nine patients, renal function decreased during therapy; at enrollment, all nine had high serum creatinine concentrations and markedly elevated plasma glycolate concentrations (> or =97.7 mg per deciliter [12.9 mmol per liter]). None of the 10 patients with normal serum creatinine concentrations at enrollment had renal injury during treatment; all 10 had plasma glycolate concentrations at or below 76.8 mg per deciliter (10.1 mmol per liter). Renal injury was independent of the initial plasma ethylene glycol concentration. The plasma concentration of glycolate and the urinary excretion of oxalate, the major metabolites of ethylene glycol, uniformly fell after the initiation of fomepizole therapy. Few adverse effects were attributable to fomepizole.

CONCLUSIONS

In patients with ethylene glycol poisoning, fomepizole administered early in the course of intoxication prevents renal injury by inhibiting the formation of toxic metabolites.

Characteristics of aldehyde dehydrogenases of certain aerobic bacteria representing human colonic flora

We have proposed the existence of a bacteriocolonic pathway for ethanol oxidation resulting in high intracolonic levels of toxic and carcinogenic acetaldehyde. This study was aimed at determining the ability of the aldehyde dehydrogenases (ALDH) of aerobic bacteria representing human colonic flora to metabolize intracolonically derived acetaldehyde. The apparent Michaelis constant (Km) values for acetaldehyde were determined in crude extracts of five aerobic bacterial strains, alcohol dehydrogenase (ADH) and ALDH activities of these bacteria at conditions prevailing in the human large intestine after moderate drinking were then compared. The effect of cyanamide, a potent inhibitor of mammalian ALDH, on bacterial ALDH activity was also studied. The apparent Km for acetaldehyde varied from 6.8 (NADP+-linked ALDH of Escherichia coli IH 13369) to 205 microM (NAD+-linked ALDH of Pseudomonas aeruginosa IH 35342), and maximal velocity varied from 6 nmol/min/mg (NAD+-linked ALDH of Klebsiella pneumoniae IH 35385) to 39 nmol/min/mg (NAD+-linked ALDH of Pseudomonas aeruginosa IH 35342). At pH 7.4, and at ethanol and acetaldehyde concentrations that may be prevalent in the human colon after moderate drinking, ADH activity in four out of five bacterial strains were 10-50 times higher than their ALDH activity. Cyanamide inhibited only NAD+-linked ALDH activity of Pseudomonas aeruginosa IH 35342 at concentrations starting from 0.1 nmM. We conclude that ALDHs of the colonic aerobic bacteria are able to metabolize endogenic acetaldehyde. However, the ability of ALDHs to metabolize intracolonic acetaldehyde levels associated with alcohol drinking is rather low. Large differences between ADH and ALDH activities of the bacteria found in this study may contribute to the accumulation of acetaldehyde in the large intestine after moderate drinking. ALDH activities of colonic bacteria were poorly inhibited by cyanamide. This study supports the crucial role of intestinal bacteria in the accumulation of intracolonic acetaldehyde after drinking alcohol. Individual variations in human colonic flora may contribute to the risk of alcohol-related gastrointestinal morbidity.

Ethylene glycol poisoning treated by intravenous 4-methylpyrazole

A 19-year-old woman was admitted 45 min after ethylene glycol (EG) ingestion. The initial serum EG concentration was 1.34 g/l (21.6 mmol/l), the anion gap 14.5, and the osmolal gap 24. Renal function was preserved (serum creatinine 75.1 micromol/l). As the patient was seen soon after poisoning, before the development of metabolic acidosis, therapy with 4-methylpyrazole (4-MP) was proposed as an antidote. 4-MP was administered via the intravenous route (7 mg/kg as loading dose, followed by 3.6, 1.2, 0.6, and 0.6 mg/kg at intervals of 12 h). 4-MP alone was effective in preventing EG biotransformation to toxic metabolites (absence of metabolic acidosis and renal injury). Ethanol therapy, hemodialysis, and sodium bicarbonate administration were not required. The half-life of EG during 4-MP therapy was 11 h, with a mean EG renal clearance of 26.9 ml/min, and a total of 65.3 g EG was eliminated unchanged in the urine. 4-MP therapy was also well tolerated.

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.

Methanol poisoning: a review and case study of four patients from central Australia

Methanol intoxication, a rare and potentially lethal form of poisoning, usually results from ingestion and occasionally inhalation of methanol. Initial symptoms of blurred vision, elongated anion gap and metabolic acidosis are typically delayed and may not at first be recognised as methanol-related complaints. Once diagnosed, treatment must be prompt and definitive. As well as general supportive care, ethanol infusion, dialysis and alkalinization from the mainstays of treatment. The cases described in this paper are compared to previous reports from other countries worldwide and contrast the variance in outcome often seen in methanol poisoning. The paper describes two tragic deaths and two lucky survivors, all of whom had consumed a cocktail of methanol and other alcoholic beverages at the same party. The ICU nurse's role in managing the methanol-intoxicated patient relies on that person's sound knowledge of the unusual biochemical reactions occurring in the body and the need to institute definitive and supportive measures to help both patient and family recover.

Kinetic interactions between 4-methylpyrazole and ethanol in healthy humans

4-Methylpyrazole (4-MP), a potent inhibitor of alcohol dehydrogenase activity, is a candidate to replace ethanol as the antidote for methanol and ethylene glycol intoxications, because it has a longer duration of action and apparently fewer adverse effects. To study a probable mutual inhibitory effect between ethanol and 4-MP on their elimination, two studies were performed in healthy human volunteers using double-blind crossover designs. In study A1 4-MP in the presumed therapeutic dose range of 10 to 20 mg/kg caused a 40% reduction in the rate of elimination of ethanol in 12 subjects given 0.5 to 0.7 g/kg of ethanol. These data suggest that such doses of 4-MP inhibit alcohol dehydrogenase activity in humans in vivo and would be effective at blocking methanol or ethylene glycol metabolism. In study B, ethanol (0.6 g/kg followed by 0.2 g/kg twice) significantly decreased the rate of elimination of 4-MP (5 mg/kg, given intravenously to four subjects). These moderate doses of ethanol also inhibited the rate of urinary excretion of 4-carboxypyrazole, the primary metabolite of 4-MP in humans. Data suggest that ethanol inhibits 4-MP metabolism, thereby increasing the duration of therapeutic blood levels of 4-MP in the body. This mutual interaction may have clinical implications, because most self-poisoned patients have also ingested ethanol. Theoretically, methanol and ethylene glycol might also show such interactions with 4-MP.

4-Methylpyrazole (4-MP) is effectively removed by haemodialysis in the pig model

The safety and pharmacokinetics of the alcohol dehydrogenase inhibitor 4-MP have recently been evaluated and its clinical use in ethylene glycol poisoning in France is promising. The dialysability of 4-MP is not known. This is important as hemodialysis is one of the cornerstones in the treatment of (late) ethylene glycol and methanol poisonings. We therefore studied the dialysability of 4-MP in the pig model. Anesthesized pigs (maintained on respirator) given 4-MP, 10 mg/kg, served as controls (n = 3) to the pigs (n = 3) given 15 mg/kg and hemodialyzed for 4 h. 4-MP plasma elimination curves for both groups were compared for 12 h and dialysance data calculated. 4-MP (MW 82) was removed by the same rate as urea (MW 60) by the 0.3 m2 dialysator, thus indicating no significant protein binding of 4-MP. The mean dialysance of 4-MP (and urea) in the three pigs were 61 (63), 51 (53) and 56 (48) ml/min, at a blood flow of 75 ml/min. The amount of 4-MP removed by hemodialysis in 4 h was 57-76 mg compared to a urinary excretion of 1-3 mg over 12 h. We conclude that the dialysability of 4-MP is significant and this must be taken into account when these two treatment procedures are combined.

4-Methylpyrazole blocks acetaminophen hepatotoxicity in the rat

STUDY OBJECTIVE

To determine whether 4-methylpyrazole inhibits the hepatotoxic effects of acetaminophen in a rat model. DESIGN AND TYPE OF PARTICIPANTS: A nonblinded experiment using male Sprague-Dawley rats.

INTERVENTIONS

Animals were divided into four groups. Groups 1 through 3 received 2,000 mg/kg acetaminophen by gavage; group 4 acted as a control. At four or eight hours, group 2 received 400 mg/kg 4-methylpyrazole; group 3 received 50 mg/kg 4-methylpyrazole. Blood samples were taken for measurements of serum AST and ALT levels. Livers were removed for microscopic examination and grading of necrosis.

RESULTS

Lower AST and ALT levels were obtained for both the 400-mg/kg (P < .01) and 50-mg/kg (P < .05) doses of 4-methylpyrazole administered four hours after acetaminophen. Although mean AST and ALT levels also were lower when 400 and 50 mg/kg 4-methylpyrazole were administered eight hours after acetaminophen, these results were not statistically significant. Median necrosis scores were 3 for rats receiving acetaminophen alone, 0.5 for those receiving acetaminophen and 400 mg/kg 4-methylpyrazole (P < .05), 1 for those receiving acetaminophen and 50 mg/kg 4-methylpyrazole (P < .05), and 0 for control rats (P < .05).

CONCLUSION

When administered four hours after a toxic dose of acetaminophen, 4-methylpyrazole significantly inhibits hepatotoxicity in the rat, as reflected by lower levels of serum transaminases and lesser degrees of hepatic necrosis.

Methanol poisoning

Methanol ingestion is an uncommon form of poisoning that can cause severe metabolic disturbances, blindness, permanent neurologic dysfunction and death. While methanol itself may be harmless, it is converted in vivo to the highly toxic formic acid. The diagnosis is sometimes elusive and requires a high index of suspicion. Because antidotal treatment is available it is important to recognize methanol poisoning promptly. The presence of metabolic acidosis associated with an increased anion gap and increased osmol gap are important laboratory findings. Specific therapeutic measures include correction of the metabolic acidosis with sodium bicarbonate and administration of enteral or parenteral ethanol to competitively inhibit the metabolic breakdown of methanol to formic acid. Hemodialysis accelerates the elimination of both methanol and formic acid and also assists in correction of the metabolic acidosis. Experimental data suggests that administration of folic acid may be of benefit by hastening the metabolism of formic acid to carbon dioxide. Prompt institution of specific therapy can probably decrease the morbidity and mortality associated with this form of poisoning.