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

Clinically relevant therapeutic approaches against acetaminophen hepatotoxicity and acute liver failure

Liver injury and acute liver failure caused by an acetaminophen (APAP) overdose is a significant clinical problem in western countries. With the introduction of the mouse model of APAP hepatotoxicity in the 1970 s, fundamental mechanisms of cell death were discovered. This included the recognition that part of the APAP dose is metabolized by cytochrome P450 generating a reactive metabolite that is detoxified by glutathione. After the partial depletion of glutathione, the reactive metabolite will covalently bind to sulfhydryl groups of proteins, which is the initiating event of the toxicity. This insight led to the introduction of N-acetyl-L-cysteine, a glutathione precursor, as antidote against APAP overdose in the clinic. Despite substantial progress in our understanding of the pathomechanisms over the last decades viable new antidotes only emerged recently. This review will discuss the background, mechanisms of action, and the clinical prospects of the existing FDA-approved antidote N-acetylcysteine, of several new drug candidates under clinical development [4-methylpyrazole (fomepizole), calmangafodipir] and examples of additional therapeutic targets (Nrf2 activators) and regeneration promoting agents (thrombopoietin mimetics, adenosine A2B receptor agonists, Wharton's Jelly mesenchymal stem cells). Although there are clear limitations of certain therapeutic approaches, there is reason to be optimistic. The substantial progress in the understanding of the pathophysiology of APAP hepatotoxicity led to the consideration of several drugs for development as clinical antidotes against APAP overdose in recent years. Based on the currently available information, it is likely that this will result in additional drugs that could be used as adjunct treatment for N-acetylcysteine.

Real-world safety and effectiveness of intravenous fomepizole in patients with ethylene glycol and methanol poisoning in Japan: results of a 7-year post-marketing surveillance study

BACKGROUND

Fomepizole is a competitive alcohol dehydrogenase inhibitor used for the treatment of ethylene glycol and methanol poisoning. We evaluated the safety and effectiveness of fomepizole in patients with ethylene glycol or methanol poisoning in Japan.

RESEARCH DESIGN AND METHODS

This retrospective post-marketing surveillance study conducted in Japan registered patients who received fomepizole intravenous infusion per the package insert (January 2015-June 2022). Endpoints included adverse drug reactions/infections (ADRs), arterial blood pH, and treatment outcomes.

RESULTS

Of 147 patients registered (91 institutions), 131 and 126 were included in the safety and effectiveness analysis sets, respectively. Mean age was 43.6 years, and 66.4% were male. Mean time from poison ingestion to treatment was 15.1 hours; 66.4% received concomitant hemodialysis. No serious ADRs were reported. ADRs were reported in seven patients; the most-reported ADR was vomiting (2.3%). Seven patients died, 105 survived without sequelae, and 19 survived with sequelae. Most common sequelae were renal failure or renal dysfunction. Mean arterial blood pH increased to 7.4 by 4 hours of treatment, remaining stable for 24 hours post-treatment.

CONCLUSIONS

Fomepizole is well tolerated and helps improve clinical outcomes in patients with ethylene glycol or methanol poisoning in Japan.

TRIAL REGISTRATION

Japanese Pharmaceutical Information Center (JapicCTI-152817).

Central Mechanisms of Acetaminophen Hepatotoxicity: Mitochondrial Dysfunction by Protein Adducts and Oxidant Stress

Acetaminophen (APAP) is an analgesic and antipyretic drug used worldwide, which is safe at therapeutic doses. However, an overdose can induce liver injury and even liver failure. Mechanistic studies in mice beginning with the seminal papers published by B.B. Brodie's group in the 1970s have resulted in important insight into the pathophysiology. Although the metabolic activation of APAP with generation of a reactive metabolite, glutathione depletion, and protein adduct formation are critical initiating events, more recently, mitochondria have come into focus as an important target and decision point of cell death. This review provides a comprehensive overview of the induction of mitochondrial superoxide and peroxynitrite formation and its propagation through a mitogen-activated protein kinase cascade, the mitochondrial permeability transition pore opening caused by iron-catalyzed protein nitration, and the mitochondria-dependent nuclear DNA fragmentation. In addition, the role of adaptive mechanisms that can modulate the pathophysiology, including autophagy, mitophagy, nuclear erythroid 2 p45-related factor 2 activation, and mitochondrial biogenesis, are discussed. Importantly, it is outlined how the mechanisms elucidated in mice translate to human hepatocytes and APAP overdose patients, and how this mechanistic insight explains the mechanism of action of the clinically approved antidote N-acetylcysteine and led to the recent discovery of a novel compound, fomepizole, which is currently under clinical development. SIGNIFICANCE STATEMENT: Acetaminophen (APAP)-induced liver injury is the most frequent cause of acute liver failure in western countries. Extensive mechanistic research over the last several decades has revealed a central role of mitochondria in the pathophysiology of APAP hepatotoxicity. This review article provides a comprehensive discussion of a) mitochondrial protein adducts and oxidative/nitrosative stress, b) mitochondria-regulated nuclear DNA fragmentation, c) adaptive mechanisms to APAP-induced cellular stress, d) translation of cell death mechanisms to overdose patients, and e) mechanism-based antidotes against APAP-induced liver injury.

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.

High-Dose Acetaminophen as a Treatment for Cancer

The use of high-dose acetaminophen (AAP) with n-acetylcysteine (NAC) rescue was studied as an anti-cancer treatment in phase I trials with promising signals of anti-tumor efficacy. Correlative analysis suggested that AAP has a free-radical-independent mechanism of anti-tumor activity-in contrast to the well-established mechanism of AAP hepatotoxicity. Subsequent "reverse translational" studies in the pre-clinical setting have identified novel mechanisms of action of high-dose AAP, including modulation of JAK-STAT signaling in both the tumor cell and the tumor immune microenvironment. Importantly, these effects are free-radical-independent and not reversed by concurrent administration of the established AAP rescue agents fomepizole and NAC. By administering high-dose AAP concurrently with fomepizole and NAC, 100-fold higher AAP levels than those of standard dosing can be achieved in mice without detected toxicity and with substantial anti-tumor efficacy against commonly used mouse models of lung and breast cancer that are resistant to standard first-line anti-cancer therapies. With these recent advances, additional clinical trials of high-dose AAP with concurrent NAC and fomepizole-based rescue are warranted.

Acetaminophen Hepatotoxicity: Paradigm for Understanding Mechanisms of Drug-Induced Liver Injury

Acetaminophen (APAP) overdose is the clinically most relevant drug hepatotoxicity in western countries, and, because of translational relevance of animal models, APAP is mechanistically the most studied drug. This review covers intracellular signaling events starting with drug metabolism and the central role of mitochondrial dysfunction involving oxidant stress and peroxynitrite. Mitochondria-derived endonucleases trigger nuclear DNA fragmentation, the point of no return for cell death. In addition, adaptive mechanisms that limit cell death are discussed including autophagy, mitochondrial morphology changes, and biogenesis. Extensive evidence supports oncotic necrosis as the mode of cell death; however, a partial overlap with signaling events of apoptosis, ferroptosis, and pyroptosis is the basis for controversial discussions. Furthermore, an update on sterile inflammation in injury and repair with activation of Kupffer cells, monocyte-derived macrophages, and neutrophils is provided. Understanding these mechanisms of cell death led to discovery of N-acetylcysteine and recently fomepizole as effective antidotes against APAP toxicity.

Nrf2 as a therapeutic target in acetaminophen hepatotoxicity: A case study with sulforaphane

Acetaminophen (APAP) overdose can cause severe liver injury and acute liver failure. The only clinically approved antidote, N-acetylcysteine (NAC), is highly effective but has a narrow therapeutic window. In the last 2 decades, activation of the transcription factor nuclear factor erythroid 2-related factor 2 (Nrf2), which regulates acute phase proteins and antioxidant defense genes, has emerged as a putative new therapeutic target against APAP hepatotoxicity. However, virtually all studies that propose Nrf2 activation as mechanism of protection used prolonged pretreatment, which is not a clinically feasible approach to treat a drug overdose. Therefore, the objective of this study was to assess if therapeutic activation of Nrf2 is a viable approach to treat liver injury after APAP overdose. We used the water-soluble Nrf2 activator sulforaphane (SFN; 5 mg/kg) in a murine model of APAP hepatotoxicity (300 mg/kg). Our results indicate that short-term treatment (≤3 h) with SFN alone did not activate Nrf2 or its target genes. However, posttreatment with SFN after APAP partially protected at 6 h likely due to more rapid activation of the Nrf2-target gene heme oxygenase-1. A direct comparison of SFN with NAC given at 1 h after APAP showed a superior protection with NAC, which was maintained at 24 h unlike with SFN. Thus, Nrf2 activators have inherent problems like the need to create a cellular stress to activate Nrf2 and delayed adaptive responses which may hamper sustained protection against APAP hepatotoxicity. Thus, compared to the more direct acting antidote NAC, Nrf2 activators are less suitable for this indication.

Fomepizole Therapy for Acetaminophen-Induced Liver Failure in an Infant

Acetaminophen overdose is common in the pediatric population. N-acetylcysteine (NAC) is effective at preventing liver injury in most patients when started shortly after the overdose. Delays to therapy increase risk of hepatotoxicity and liver failure that may necessitate organ transplant. Animal studies have demonstrated fomepizole may provide added benefit in acetaminophen overdose because of its ability to block the metabolic pathway that produces the toxic acetaminophen metabolite and downstream inhibition of oxidative stress pathways that lead to cell death. Several adult case reports describe use of fomepizole in patients at higher risk for poor outcomes despite NAC. We describe a case of a 7-month-old female who presented in acute liver failure with persistently elevated acetaminophen concentration secondary to repeated supratherapeutic doses of acetaminophen to manage fever. Fomepizole and NAC antidotes were used in the management of the patient. She fully recovered despite demonstrating multiple markers of poor outcome on initial presentation. Although randomized trials are lacking, this case suggests that fomepizole may safely provide additional benefit in pediatric patients at risk for severe acetaminophen toxicity.

Advances in the understanding of acetaminophen toxicity mechanisms: a clinical toxicology perspective

INTRODUCTION

Acetaminophen (paracetamol) is a commonly used analgesic and antipyretic agent, which is safe in therapeutic doses. Acetaminophen poisoning due to self-harm or repeated supratherapeutic ingestion is a common cause of acute liver injury. Acetylcysteine has been a mainstay of treatment for acetaminophen poisoning for decades and is efficacious if administered early. However, treatment failures occur if administered late, in 'massive' overdoses or in high-risk patients.

AREAS COVERED

This review provides an overview of the mechanisms of toxicity of acetaminophen poisoning (metabolic and oxidative phase) and how this relates to the assessment and treatment of the acetaminophen poisoned patient. The review focuses on how these advances offer further insight into the utility of novel biomarkers and the role of proposed adjunct treatments.

EXPERT OPINION

Advances in our understanding of acetaminophen toxicity have allowed the development of novel biomarkers and a better understanding of how adjunct treatments may prevent acetaminophen toxicity. Newly proposed adjunct treatments like fomepizole are being increasingly used without robust clinical trials. Novel biomarkers (not yet clinically available) may provide better assessment of these newly proposed adjunct treatments, particularly in clinical trials. These advances in our understanding of acetaminophen toxicity and liver injury hold promise for improved diagnosis and treatment.

Extracorporeal treatment for ethylene glycol poisoning: systematic review and recommendations from the EXTRIP workgroup

Ethylene glycol (EG) is metabolized into glycolate and oxalate and may cause metabolic acidemia, neurotoxicity, acute kidney injury (AKI), and death. Historically, treatment of EG toxicity included supportive care, correction of acid-base disturbances and antidotes (ethanol or fomepizole), and extracorporeal treatments (ECTRs), such as hemodialysis. With the wider availability of fomepizole, the indications for ECTRs in EG poisoning are debated. We conducted systematic reviews of the literature following published EXTRIP methods to determine the utility of ECTRs in the management of EG toxicity. The quality of the evidence and the strength of recommendations, either strong ("we recommend") or weak/conditional ("we suggest"), were graded according to the GRADE approach. A total of 226 articles met inclusion criteria. EG was assessed as dialyzable by intermittent hemodialysis (level of evidence = B) as was glycolate (Level of evidence = C). Clinical data were available for analysis on 446 patients, in whom overall mortality was 18.7%. In the subgroup of patients with a glycolate concentration ≤ 12 mmol/L (or anion gap ≤ 28 mmol/L), mortality was 3.6%; in this subgroup, outcomes in patients receiving ECTR were not better than in those who did not receive ECTR. The EXTRIP workgroup made the following recommendations for the use of ECTR in addition to supportive care over supportive care alone in the management of EG poisoning (very low quality of evidence for all recommendations): i) Suggest ECTR if fomepizole is used and EG concentration > 50 mmol/L OR osmol gap > 50; or ii) Recommend ECTR if ethanol is used and EG concentration > 50 mmol/L OR osmol gap > 50; or iii) Recommend ECTR if glycolate concentration is > 12 mmol/L or anion gap > 27 mmol/L; or iv) Suggest ECTR if glycolate concentration 8-12 mmol/L or anion gap 23-27 mmol/L; or v) Recommend ECTR if there are severe clinical features (coma, seizures, or AKI). In most settings, the workgroup recommends using intermittent hemodialysis over other ECTRs. If intermittent hemodialysis is not available, CKRT is recommended over other types of ECTR. Cessation of ECTR is recommended once the anion gap is < 18 mmol/L or suggested if EG concentration is < 4 mmol/L. The dosage of antidotes (fomepizole or ethanol) needs to be adjusted during ECTR.

Fomepizole should be used more liberally in paracetamol overdose

Growing clinical and basic science data support the use of fomepizole as an adjunct to N-acetylcysteine in paracetamol poisoning. This safe antidote may be helpful in severely poisoned patients.

Resveratrol in Liquor Exacerbates Alcoholic Liver Injury with a Reduced Therapeutic Effect in Mice: An Unsupervised Herbal Wine Habit Is Risky

People in Eastern countries hold a tradition of soaking herbal medicine in wine; however, the efficacy and safety of herbal wine have not been rigorously assessed. By assessing the efficacy of resveratrol (RSV) in ethanol against alcoholic liver disease (ALD) in mice, we aimed to offer a perspective on the use of herbal wine. To simulate the behaviour of herbal wine users, RSV (15 mg/kg) soaked in ethanol (RSV-alcohol) was administrated via gavage to the mice, here with alcohol consumption-induced ALD. RSV soaked in water (RSV-water) was the treatment control. The efficacy and safety of RSV on ALD were evaluated. Compared with the RSV-water group, a higher rate of mortality was found in the RSV-alcohol group (50.0% vs. 20.0%), which also exhibited more severe liver injury. RSV significantly increased the exposure of alcohol by 126.0%, which was accompanied by a significant inhibition of the ethanol metabolic pathway. In contrast, alcohol consumption significantly reduced exposure to RSV by 95.0%. Alcohol consumption had little effect on the expression of drug-metabolizing enzymes in RSV; however, alcohol seemed to reduce the absorption of RSV. RSV in liquor exacerbates alcoholic liver injury and has a reduced therapeutic effect, suggesting that the habit of herbal wine use without supervision is risky.

Acetaminophen toxicity and overdose: current understanding and future directions for NAC dosing regimens

INTRODUCTION

Although N-acetyl-cysteine (NAC) has long been used for the treatment of acetaminophen poisoning/overdose, the optimal NAC dosing regimen for varying patterns or severity of the poisoning/overdose is still unknown.

AREAS COVERED

Relevant literature was searched for in the MEDLINE (from 1964 until August 31^st, 2022), SCOPUS (from 2004 until August 31^st, 2022) and GOOGLE SCHOLAR (from 2004 until August 31^st, 2022) databases, without restriction in terms of publication date. The inclusion criteria were: original clinical studies reporting results, and studies investigating efficacy and safety of NAC dosing regimens in case(s) of overdose or poisoning with acetaminophen.

EXPERT OPINION

For a more effective treatment of acetaminophen poisoning in the future, it will be crucial to advance the technology of measuring acetaminophen, its metabolites and NAC in the serum, preferably with the point-of-care technique, so that in real time it can be continuously assessed whether it is necessary to administer NAC, and further to increase the dose of NAC and extend the duration of its administration, or not.

Fomepizole as an adjunctive therapy for acetaminophen poisoning: cases reported to the toxicology investigators consortium (ToxIC) database 2015-2020

INTRODUCTION

Fomepizole inhibits formation of toxic acetaminophen (APAP) metabolites and may prevent or reverse mitochondrial toxicity. Given these mechanisms, it may be beneficial in patients with severe APAP toxicity. Current patterns of use for this indication are not well-studied.

METHODS

This is a secondary analysis of patients enrolled in the Toxicology Investigators Consortium (ToxIC) database from January 2015 to July 2020. We queried cases in which APAP was listed as an ingested agent and fomepizole was also administered. We excluded cases in which APAP was not the primary agent, N-acetylcysteine (NAC) was not administered, or fomepizole was explicitly administered for another indication. Additionally, we sent a survey to each ToxIC site that administered fomepizole for APAP toxicity to better understand when, why, and how they were using it for this indication.

RESULTS

Twenty-five cases of fomepizole administration following an APAP ingestion met our inclusion criteria. There were one to four cases per year between 2015 and 2019 and eight cases in 2020. Seventeen of 25 (68%) cases were for a known acute ingestion. Eighteen of 25 (72%) patients developed hepatotoxicity (AST or ALT > 1000 IU/L) and 10 of 25 (40%) developed coagulopathy (PT > 15s). This was an ill patient population, with 18 of 25 (72%) developing metabolic acidosis (pH <7.20), 12 of 25 (48%) were intubated, 9 of 25 (36%) receiving vasopressors, and 6 of 25 (24%) receiving continuous renal replacement therapy. Overall, mortality was 24%.

CONCLUSION

The use of fomepizole is increasing in frequency in a small subset of critically ill and acutely APAP-poisoned patients.

Molecular pathogenesis of acetaminophen-induced liver injury and its treatment options

Acetaminophen, also known as N-acetyl-p-aminophenol (APAP), is commonly used as an antipyretic and analgesic agent. APAP overdose can induce hepatic toxicity, known as acetaminophen-induced liver injury (AILI). However, therapeutic doses of APAP can also induce AILI in patients with excessive alcohol intake or who are fasting. Hence, there is a need to understand the potential pathological mechanisms underlying AILI. In this review, we summarize three main mechanisms involved in the pathogenesis of AILI: hepatocyte necrosis, sterile inflammation, and hepatocyte regeneration. The relevant factors are elucidated and discussed. For instance, N-acetyl-p-benzoquinone imine (NAPQI) protein adducts trigger mitochondrial oxidative/nitrosative stress during hepatocyte necrosis, danger-associated molecular patterns (DAMPs) are released to elicit sterile inflammation, and certain growth factors contribute to liver regeneration. Finally, we describe the current potential treatment options for AILI patients and promising novel strategies available to researchers and pharmacists. This review provides a clearer understanding of AILI-related mechanisms to guide drug screening and selection for the clinical treatment of AILI patients in the future.

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.

Pirfenidone attenuates acetaminophen-induced liver injury via suppressing c-Jun N-terminal kinase phosphorylation

Acetaminophen (APAP)-induced liver injury is the most frequent cause of acute liver failure in Western countries. Pirfenidone (PFD), an orally bioavailable pyridone derivative, is clinically used for idiopathic pulmonary fibrosis treatment and has antifibrotic, anti-inflammatory, and antioxidant effects. Here we examined the PFD effect on APAP-induced liver injury. In a murine model, APAP caused serum alanine aminotransferase elevation attenuated by PFD treatment. We performed terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) and vital propidium iodide (PI) stainings simultaneously. APAP induced TUNEL-positive/PI-negative necrosis around the central vein and subsequent TUNEL-negative/PI-positive oncotic necrosis with hemorrhage and caused the upregulation of hypercoagulation- and hypoxia-associated gene expressions. PFD treatment suppressed these findings. Western blotting revealed PFD suppressed APAP-induced c-Jun N-terminal kinase (JNK) phosphorylation despite no effect on JNK phosphatase expressions. In conclusion, simultaneous TUNEL and vital PI staining is useful for discriminating APAP-induced necrosis from typical oncotic necrosis. Our results indicated that PFD attenuated APAP-induced liver injury by suppressing TUNEL-positive necrosis by directly blocking JNK phosphorylation. PFD is promising as a new option to prevent APAP-induced liver injury.

Fomepizole dosing during continuous renal replacement therapy - an observational study

BACKGROUND

Fomepizole is the preferred antidote for treatment of methanol and ethylene glycol poisoning, acting by inhibiting the formation of the toxic metabolites. Although very effective, the price is high and the availability is limited. Its availability is further challenged in situations with mass poisonings. Therefore, a 50% reduced maintenance dose for fomepizole during continuous renal replacement therapy (CRRT) was suggested in 2016, based on pharmacokinetic data only. Our aim was to study whether this new dosing for fomepizole during CRRT gave plasma concentrations above the required 10 µmol/L. Secondly, we wanted to study the elimination kinetics of fomepizole during CRRT, which has never been studied before.

METHODS

Prospective observational study of adult patients treated with fomepizole and CRRT. We collected samples from arterial line (pre-filter) = plasma concentration, post-filter and dialysate for fomepizole measurements. Fomepizole was measured using high-pressure liquid chromatography with a reverse phase column.

RESULTS

Ten patients were included in the study. Seven were treated with continuous veno-venous hemodialysis (CVVHD) and three with continuous veno-venous hemodiafiltration (CVVHDF). Ninety-eight percent of the plasma samples were above the minimum plasma concentration of 10 µmol/L. Fomepizole was removed during CRRT with a median saturation/sieving coefficient of 0.85 and dialysis clearance of 28 mL/min.

CONCLUSION

Fomepizole was eliminated during CCRT. The new dosing recommendations for fomepizole and CRRT appeared safe, by maintaining the plasma concentration above the minimum value of 10 µmol/L. Based on these data, the fomepizole maintenance dose during CRRT could be reduced to half as compared to intermittent hemodialysis.

Oxidant Stress and Acetaminophen Hepatotoxicity: Mechanism-Based Drug Development

Significance: Acetaminophen (APAP) is one of the quantitively most consumed drugs worldwide. Although safe at therapeutic doses, intentional or unintentional overdosing occurs frequently causing severe liver injury and even liver failure. In the United States, 50% of all acute liver failure cases are caused by APAP overdose. However, only one antidote with a limited therapeutic window, N-acetylcysteine, is clinically approved. Thus, more effective therapeutic interventions are urgently needed. Recent Advances: Although APAP hepatotoxicity has been extensively studied for almost 50 years, particular progress has been made recently in two areas. First, there is now a detailed understanding of involvement of oxidative and nitrosative stress in the pathophysiology, with identification of the reactive species involved, their initial generation in mitochondria, amplification through the c-Jun N-terminal kinase pathway, and the mechanisms of cell death. Second, it was demonstrated in human hepatocytes and through biomarkers in vivo that the mechanisms of liver injury in animals accurately reflect the human pathophysiology, which allows the translation of therapeutic targets identified in animals to patients. Critical Issues: For progress, solid understanding of the pathophysiology of APAP hepatotoxicity and of a drug's targets is needed to identify promising new therapeutic intervention strategies and drugs, which may be applied to humans. Future Directions: In addition to further refine the mechanistic understanding of APAP hepatotoxicity and identify additional drugs with complementary mechanisms of action to prevent cell death, more insight into the mechanisms of regeneration and developing of drugs, which promote recovery, remains a future challenge. Antioxid. Redox Signal. 35, 718-733.

Delayed administration of N-acetylcysteine blunts recovery after an acetaminophen overdose unlike 4-methylpyrazole

N-acetylcysteine (NAC) is the only clinically approved antidote against acetaminophen (APAP) hepatotoxicity. Despite its efficacy in patients treated early after APAP overdose, NAC has been implicated in impairing liver recovery in mice. More recently, 4-methylpyrazole (4MP, Fomepizole) emerged as a potential antidote in the mouse APAP hepatotoxicity model. The objective of this manuscript was to verify the detrimental effect of NAC and its potential mechanism and assess whether 4MP has the same liability. C57BL/6J mice were treated with 300 mg/kg APAP; 9h after APAP and every 12h after that, the animals received either 100 mg/kg NAC or 184.5 mg/kg 4MP. At 24 or 48h after APAP, parameters of liver injury, mitochondrial biogenesis and cell proliferation were evaluated. Delayed NAC treatment had no effect on APAP-induced liver injury at 24h but reduced the decline of plasma ALT activities and prevented the shrinkage of the areas of necrosis at 48h. This effect correlated with down-regulation of key activators of mitochondrial biogenesis (AMPK, PGC-1α, Nrf1/2, TFAM) and reduced expression of Tom 20 (mitochondrial mass) and PCNA (cell proliferation). In contrast, 4MP attenuated liver injury at 24h and promoted recovery at 48h, which correlated with enhanced mitochondrial biogenesis and hepatocyte proliferation. In human hepatocytes, 4MP demonstrated higher efficacy in preventing cell death compared to NAC when treated at 18h after APAP. Thus, due to the wider treatment window and lack of detrimental effects on recovery, it appears that at least in preclinical models, 4MP is superior to NAC as an antidote against APAP overdose.

Massive Acetaminophen Overdose Treated Successfully with N-Acetylcysteine, Fomepizole, and Hemodialysis

Acetaminophen overdose is one of the most common causes of acute hepatic failure in the developed world. There is strong evidence for N-acetylcysteine (NAC) as a safe and effective antidote for acetaminophen toxicity. However, there is less clarity in the management of massive overdoses (acute, single ingestions > 500 mg/kg with 4-hour equivalent concentrations ~6000 μmol/L) which are often associated with metabolic acidosis and multiorgan dysfunction. In such ingestions, the role of adjuvant treatments such as fomepizole and extracorporeal removal is unclear. We present a case of a 20-year-old female presenting with an acute ingestion of over 120 grams (1764.7 mg/kg) and an acetaminophen concentration of 5880 μmol/L who developed refractory shock, decreased level of consciousness, and metabolic acidosis requiring mechanical ventilation and vasopressor support. She was treated with gastric decontamination with activated charcoal, IV NAC, fomepizole, and hemodialysis. The patient had complete clearance of acetaminophen by 32 hours after presentation and normalization of her acid base and hemodynamic status without any organ failure. This case highlights the potential benefit of a triple strategy of NAC, fomepizole, and early hemodialysis in massive acetaminophen overdose, potentially sparing complications of prolonged intubation and ICU hospitalization.

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.

Novel strategies for the treatment of acetaminophen hepatotoxicity

INTRODUCTION

Acetaminophen (APAP) hepatotoxicity is the leading cause of acute liver failure in the western world. Despite extensive investigations into the mechanisms of cell death, only a single antidote, N-acetylcysteine, is in clinical use. However, there have recently been more efforts made to translate mechanistic insight into identification of therapeutic targets and potential new drugs for this indication.

AREAS COVERED

After a short review of the key events in the pathophysiology of APAP-induced liver injury and recovery, the pros and cons of targeting individual steps in the pathophysiology as therapeutic targets are discussed. While the re-purposed drug fomepizole (4-methylpyrazole) and the new entity calmangafodipir are most advanced based on the understanding of their mechanism of action, several herbal medicine extracts and their individual components are also considered.

EXPERT OPINION

Fomepizole (4-methylpyrazole) is safe and has shown efficacy in preclinical models, human hepatocytes and in volunteers against APAP overdose. The safety of calmangafodipir in APAP overdose patients was shown but it lacks solid preclinical efficacy studies. Both drugs require a controlled phase III trial to achieve regulatory approval. All studies of herbal medicine extracts and components suffer from poor experimental design, which questions their clinical utility at this point.

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.