Safety and Efficacy of the SNAP 12-hour Acetylcysteine Regimen for the Treatment of Paracetamol Overdose

Assessing the frequency and types of errors involved in the use of a modified intravenous N-acetylcysteine protocol for acetaminophen overdose

BACKGROUND

Acetaminophen overdose is a leading cause of acute liver failure in developing countries. N-acetylcysteine (NAC) is a highly effective antidote for acetaminophen hepatotoxicity, typically initiated in the emergency department. Due to a known high rate of errors with the standard three-bag IV NAC protocol, in 2019, the Ontario Poison Center changed to a modified 3% IV NAC one-bag protocol. This study was undertaken to determine the frequency and types of errors associated with the use of this protocol.

METHODS

Data were gathered via chart review of Ontario Poison Centre electronic medical record cases identified as receiving IV NAC for acetaminophen overdose between August 1 and September 30, 2022. 218 total charts were identified, and 188 were deemed eligible based on inclusion and exclusion criteria.

RESULTS

Errors were identified in 25% of charts, consisting of dosing errors in 11.7%, stopping errors in 9.0%, initiation errors in 3.7%, and interruptions in therapy in 3.2%. Dosing errors were the most common type of error (44.4%), with overdoses occurring three times more than underdoses. Errors were identified at 39% of geographic locations in the charts reviewed, with similar frequency in Ontario, Manitoba, and Nunavut. Clinical outcomes were similar in charts with and without errors.

INTERPRETATION

The rate of errors identified with this 3% IV NAC one-bag protocol is lower than reported for the standard three-bag protocol, but remains high due to dosing errors. Previously reported issues with prolonged interruptions in therapy with the standard three-bag protocol were low with the current 3% one-bag protocol. Although severe outcomes are rare, IV NAC overdose can be fatal. Identifying local factors in emergency departments that can contribute to administration errors (i.e., dose calculation, pump programming issues) can enhance the safety of this important antidote.

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.

Fifty years of paracetamol (acetaminophen) poisoning: the development of risk assessment and treatment 1973-2023 with particular focus on contributions published from Edinburgh and Denver

INTRODUCTION

Fifty years ago, basic scientific studies and the availability of assay methods made the assessment of risk in paracetamol (acetaminophen) poisoning possible. The use of the antidote acetylcysteine linked to new methods of risk assessment transformed the treatment of this poisoning. This review will describe the way in which risk assessment and treatments have developed over the last 50 years and highlight the remaining areas of uncertainty.

METHODS

A search of PubMed and its subsidiary databases revealed 1,166 references published in the period 1963-2023 using the combined terms "paracetamol", "poisoning", and "acetylcysteine". Focused searches then identified 170 papers dealing with risk assessment of paracetamol poisoning, 141 with adverse reactions to acetylcysteine and 114 describing different acetylcysteine regimens. To manage the extensive literature, we focused mainly on contributions made by the authors during their time in Edinburgh and Denver.

DOSE AND CONCENTRATION RESPONSE

The key relationship between paracetamol dose and toxicity risk was established in 1971 and led to the development of the Rumack-Matthew nomogram from data collected in Edinburgh.

MECHANISMS OF TOXICITY

A series of papers on the mechanisms of toxicity were published in 1973, and these showed that paracetamol hepatotoxicity was caused by the formation of a toxic intermediate epoxide metabolite normally detoxified by glutathione but which, in excess, was bound covalently to hepatic enzymes and proteins. An understanding of the relationship between the rate of paracetamol metabolism, paracetamol concentration, and toxic hazard in humans soon followed.

ANTIDOTE DEVELOPMENT AND EFFICACY IN PATIENTS

These discoveries were followed by the testing of a range of sulfhydryl-donors in animals and "at risk" patients. Acetylcysteine was developed as the lead intravenous antidote in the United Kingdom. The license holder in the United States refused to make an intravenous formulation. Thus, oral acetylcysteine became the antidote trialed in the United States National Multicenter Study. Intravenous acetylcysteine regimens used initially in the United Kingdom and subsequently in the United States used loading doses of 150 mg/kg over 15 minutes or one hour, 50 mg/kg over four hours, and 100 mg/kg over 16 hours. These regimens were associated with adverse drug reactions (nausea, vomiting and anaphylactoid reactions) and hence, treatment interruption. Newer dosing regimens now give loading doses more slowly. One, the Scottish and Newcastle Anti-emetic Pretreatment protocol, using an acetylcysteine regimen of 100 mg/kg over two hours followed by 200 mg/kg over 10 hours, has been widely adopted in the United Kingdom. A cohort comparison study suggests this regimen has comparable efficacy to standard regimens and offers opportunities for selective higher acetylcysteine dosing.

RISK ASSESSMENT AT PRESENTATION

No dose-ranging studies with acetylcysteine were done, and no placebo-controlled studies were performed. Thus, there is uncertainty regarding the optimal dose of acetylcysteine, particularly in patients ingesting very large overdoses of paracetamol. The choice of intervention concentration on the Rumack-Matthew nomogram has important consequences for the proportion of patients treated. The United States National Multicenter Study used a "treatment" line starting at 150 mg/L (992 µmol/L) at 4 hours post overdose, extending to 24 hours with a half-life of 4 hours, now standard there, and subsequently adopted in Australia and New Zealand. In the United Kingdom, the treatment line was initially 200 mg/L (1,323 µmol/L) at 4 hours (the Rumack-Matthew "risk" line). In 2012, the United Kingdom Medicines and Healthcare products Regulatory Agency lowered the treatment line to 100 mg/L (662 µmol/L) at 4 hours for all patients, increasing the number of patients admitted and treated at a high cost. Risk assessment is a key issue for ongoing study, particularly following the development of potential new antidotes that may act in those at greatest risk. The development of biomarkers to assess risk is ongoing but has yet to reach clinical trials.

CONCLUSION

Even after 50 years, there are still areas of uncertainty. These include appropriate acetylcysteine doses in patients who ingest different paracetamol doses or multiple (staggered) ingestions, early identification of at-risk patients, and optimal treatment of late presenters.

Is Two Better Than Three? A Systematic Review of Two-bag Intravenous N-acetylcysteine Regimens for Acetaminophen Poisoning

Introduction

Acetaminophen poisoning is commonly treated by emergency physicians. First-line therapy is N-acetylcysteine (NAC), traditionally administered intravenously via a US Food and Drug Administration (FDA)-approved three-bag protocol in which each bag has a unique concentration and infusion duration. Recently, simplified, off-label two-bag NAC infusion protocols have become more common. The purpose of this review is to summarize the effectiveness and safety of two-bag NAC.

Methods

We undertook a comprehensive search of PubMed, EMBASE, and MEDLINE from inception to December 13, 2022, for articles describing human acetaminophen poisonings treated with two-bag NAC, defined as any regimen involving two discrete infusions in two separate bags. Outcomes included effectiveness (measured by incidence of liver injury); incidence of non-allergic anaphylactoid reactions (NAAR); gastrointestinal, cutaneous, and systemic reactions; treatments for NAARs; incidence of NAC-related medication errors; and delays or interruptions in NAC administration.

Results

Twelve articles met final inclusion, 10 of which compared two-bag NAC to the three-bag regimen. Nine articles evaluated the two-bag/20-hour regimen, a simplified version of the FDA-approved three-bag regimen in which the traditional first and second bags are combined into a single four-hour infusion. Nine articles assessed comparative effectiveness of two-bag NAC in terms of liver injury, most commonly assessed for by incidence of hepatotoxicity (aspartate aminotransferase or alanine aminotransferase >1,000 international units per liter). No difference in liver injury was observed between two-bag and three-bag regimens. Of nine articles comparing incidence of NAARs, eight demonstrated statistically fewer NAARs with two-bag regimens, and one showed no difference. In seven articles evaluating treatment for NAARs (antihistamines, corticosteroids, epinephrine), all showed that patients received fewer medications for NAARs with two-bag NAC. Three articles evaluated NAC-related medication errors; two demonstrated no difference, while one study evaluating only children showed fewer errors with two-bag NAC. Two studies evaluated delays and/or interruptions in NAC infusions; both favored two-bag NAC.

Conclusion

For patients with acetaminophen poisoning, two-bag NAC regimens appear to have similar outcomes to the traditional three-bag regimen in terms of liver injury. Two-bag NAC regimens are associated with fewer adverse events and fewer treatments for those events than the three-bag regimen and fewer interruptions in antidotal therapy.

War and disaster are forcing a major rethink around mass casualty management

Mass casualty events (MASCAL) do not follow the same rules as typical major incidents. In the West at least, the latter often occur in stable, networked trauma systems, whereas MASCAL are characterised by overwhelming numbers of patients, compounded by protracted scene and transport times, decompensated response systems and significant disruption to infrastructure, command and control.This paper describes the 8Ds approach being taken by the UK Defence Medical Services and the North Atlantic Treaty Organization Emergency Medicine Panel framework to approach MASCAL. The eight domains were derived from literature about management of casualties in the World Wars, and also from approaches taken by civilian health systems as they struggle to manage increasing demand. They are: distribute; decompress; delay; delegate; deliver faster and deliver better; dynamic levels of care; and de-escalate These domains will allow a structured approach to research and innovate around MASCAL, informing better guidelines for their management.

Developing new antidotes for poisons with existing effective treatments: a case study of fomepizole in paracetamol poisoning

INTRODUCTION

Acetylcysteine is the only effective and licensed therapy for paracetamol poisoning. However, acetylcysteine loses efficacy if treatment is delayed 8-12 hours after paracetamol ingestion, and there is also uncertainty as to whether the dose should be increased in high-risk paracetamol ingestions. Studies have identified potential therapeutic targets, including enzymes that metabolize paracetamol; the pathways causing mitochondrial toxicity via c-Jun N-terminal kinases or superoxide generation; and other specific targets, such as nuclear factor-erythroid factor 2-dependent gene induction and autophagy. With this range of potential additional therapies, how should the speciality of clinical toxicology approach the development of new antidotes for this common poisoning?

HISTORICAL BACKGROUND

When the first treatments for paracetamol toxicity were developed, the clinical trial and ethical basis of practice were different from today. Acetylcysteine was never subjected to placebo-controlled studies, even by the United States Food and Drug Administration, as it was presumed that the toxicity of high paracetamol concentrations was so evident that placebo-controlled studies were unethical. Thus, the absolute benefit of acetylcysteine remains unknown. In addition, no dose-ranging studies of acetylcysteine in patients were ever done. The weakness of assessing the efficacy of additional antidotes in small groups of patients with moderate poisoning is illustrated by the use of cimetidine in paracetamol poisoning.

CURRENT APPROACHES TO DRUG (AND ANTIDOTE) DEVELOPMENT

The approach required by regulatory authorities today relies on several important steps. First, a clear target for therapeutic effect is sought, normally in a laboratory model. Next, a 'proof of principle' study is required to demonstrate that the target is 'druggable'. Finally, clinical studies to confirm proof of principle applies in humans, followed by a controlled trial with matched patient groups with sufficient power to demonstrate the clinical outcome being sought. Such patient studies can be expensive to conduct, and non-commercial groups suffer the risk of not being funded.

FOMEPIZOLE

Fomepizole prevents paracetamol-induced hepatic toxicity in mice by inhibiting cytochrome P4502E1, thereby preventing the conversion of paracetamol to its toxic metabolite. Fomepizole also inhibits c-Jun N-terminal kinases, a key pathway in the downstream toxicity on the mitochondria. The present evidence of efficacy in humans is based on small case series with no control groups. The availability of a licensed indication has facilitated off-label use of fomepizole in an unproven indication.

CONCLUSIONS

Paracetamol poisoning is common, and randomized, controlled clinical trials are possible. The benefit of fomepizole can only be shown by such a study. As clinical trials using fomepizole as an added therapy to acetylcysteine are recruiting in the United States, these should be supported by all clinical toxicologists. In the interim, the publication of small case series using fomepizole should be discouraged by journals.

Hospital admissions for paracetamol poisoning declined following codeine re-scheduling in Australia

BACKGROUND

Codeine was restricted to prescription only in Australia in 2018. This intervention aimed to reduce harms from codeine dependance and use, including toxicity from co-formulated paracetamol. We aimed to quantify the impact of this intervention on paracetamol poisoning hospital admissions in a national hospital admissions database.

METHODS

We analyzed the number of paracetamol overdoses resulting in hospital admissions from the Australian Institute of Health and Welfare National Hospital Morbidity Database, January 2011 to June 2020. We used interrupted time series analysis to quantify the effect of codeine re-scheduling on the monthly number of paracetamol poisoning-related hospital admissions in Australia. We compared paracetamol poisonings with no opioid combinations, and poisonings with probable paracetamol-codeine combinations.

RESULTS

There was an immediate and sustained decrease (level shift) in the number of paracetamol poisoning-related hospital admissions following codeine re-scheduling (RR=0.85; 95% CI 0.80-0.89). This reduction was due to the decrease in poisonings with likely paracetamol-codeine combinations (RR=0.62; 95% CI 0.57-0.67) while there was no change in other paracetamol poisonings (RR=0.91; 95% CI 0.96-1.01).

CONCLUSION

Codeine re-scheduling in Australia appears to have reduced paracetamol poisoning-related hospital admissions.

SNAPTIMED study: does the Scottish and Newcastle Antiemetic Protocol achieve timely intervention and management from the emergency department to discharge for paracetamol poisoning?

BACKGROUND

This study aimed to establish whether the modified 12-hour Scottish and Newcastle Antiemetic Protocol (SNAP) for paracetamol poisoning is associated with improvement in hospital length of stay (LoS), as well as to validate the performance of the protocol for the prevention of anaphylactoid reactions and total infusion duration.

METHODS

Retrospective chart review from 25 March 2019 to 25 September 2020. Patients aged 16 or older with a diagnosis of suspected or confirmed paracetamol overdose were included in the analysis if they received treatment for paracetamol poisoning, and the protocol used could be identified. Data were collected for LoS, number of extended treatment infusions used and evidence of anaphylactoid reaction.

RESULTS

1167 records were assessed for eligibility, and 294 were included for analysis. Use of the SNAP was associated with a statistically significant reduction in LoS of -8.8 hours (95% CI -12.6 to -2.0), and a reduced risk of anaphylactoid reaction (Number Needed to Treat=10).

CONCLUSION

In this retrospective study, use of the SNAP reduced the duration of inpatient admissions and rate of anaphylactoid reactions.

Large paracetamol overdose-Higher dose acetylcysteine is required

Paracetamol poisoning continues to be a worldwide problem and, despite the availability of an effective antidote, acetylcysteine (NAC), the optimal way to use this antidote, particularly following very large doses of paracetamol, has not been established. Recent case series have shown an increased toxicity from high doses of paracetamol, even in those receiving prompt NAC therapy, particularly in patients above the 300 mg/L nomogram treatment line. Clinical trial evidence supporting shorter NAC dosing now allows the possibility for intensifying treatment without the risk of very high rates of ADRs. New biomarkers also show the possibility of early identification of patients at risk of liver injury who might also benefit from increased intensity treatment. This article discusses these data and proposes a logical therapy for increasing NAC dosing which now requires clinical trial testing.

Large paracetamol overdose - Higher dose NAC is NOT required

Paracetamol overdose is common in developed countries but less than 10% involve large ingestions exceeding 30 g or 500 mg/kg. High dose acetylcysteine (NAC) has been proposed in patients taking large paracetamol overdoses based on reports of hepatotoxicity despite early initiation of NAC treatment with the commonly used 300 mg/kg intravenous acetylcysteine regimen. The evidence from cohorts of patients treated with the standard NAC regimen after large paracetamol overdoses shows that it is effective in most patients. A small study in patients with paracetamol overdoses of 40 g or more and paracetamol concentrations above the 300 mg/L nomogram line showed that modification of the standard NAC regimen to provide a total of 400-500 mg/kg NAC over 21-22 h may reduce the risk of hepatotoxicity (peak ALT > 1000 IU/L) but the impact on development of hepatic failure, liver transplantation and mortality with this approach is presently unknown. Better risk stratification of patients taking paracetamol overdose may allow higher dose NAC and adjunctive treatments such as CYP2E1 inhibition and extracorporeal removal of paracetamol to be targeted to those patients at the highest risk of hepatotoxicity after a large paracetamol overdose.

Paracetamol (acetaminophen) overdose and hepatotoxicity: mechanism, treatment, prevention measures, and estimates of burden of disease

INTRODUCTION

Paracetamol is one of the most used medicines worldwide and is the most common important poisoning in high-income countries. In overdose, paracetamol causes dose-dependent hepatotoxicity. Acetylcysteine is an effective antidote, however despite its use hepatotoxicity and many deaths still occur.

AREAS COVERED

This review summarizes paracetamol overdose and toxicity (including mechanisms, risk factors, risk assessment, and treatment). In addition, we summarize the epidemiology of paracetamol overdose worldwide. A literature search on PubMed for poisoning epidemiology and mortality from 1 January 2017 to 26 October 2022 was performed to estimate rates of paracetamol overdose, liver injury, and deaths worldwide.

EXPERT OPINION

Paracetamol is widely available and yet is substantially more toxic than other analgesics available without prescription. Where data were available, we estimate that paracetamol is involved in 6% of poisonings, 56% of severe acute liver injury and acute liver failure, and 7% of drug-induced liver injury. These estimates are limited by lack of available data from many countries, particularly in Asia, South America, and Africa. Harm reduction from paracetamol is possible through better identification of high-risk overdoses, and better treatment regimens. Large overdoses and those involving modified-release paracetamol are high-risk and can be targeted through legislative change.

Toxicology in the emergency department: what's new?

Intentional and accidental drug overdose, recreational drug use and exposure to toxic substances are common reasons for people presenting to emergency departments. Although the mortality rate associated with these presentations is low in the UK, they can lead to significant morbidity and prolonged hospital admissions.

This review discusses new developments in the management of paracetamol overdose. Several new protocols for the infusion of acetylcysteine, the antidote for paracetamol overdose, have been proposed in the past decade and evaluated in clinical studies. The 12-hour Scottish and Newcastle Acetylcysteine Protocol regimen and 20-hour Australian two-infusion bag protocol have been widely adopted into clinical practice and endorsed in national guidelines because of their shorter duration, reduction in adverse effects and efficacy in treating overdose. This article includes a care pathway that can facilitate the implementation of the Scottish and Newcastle Acetylcysteine Protocol.

This article also discusses the emergency management of ingested button batteries, describes the emerging threat of novel psychoactive substances, and provides an update on new UK antidote guidelines. Further up-to-date guidance on management of clinical toxicology is available to healthcare professionals on the internet database TOXBASE.

MRI Detection of Hepatic N-Acetylcysteine Uptake in Mice

This proof-of-concept study looked at the feasibility of using a thiol–water proton exchange (i.e., CEST) MRI contrast to detect in vivo hepatic N-acetylcysteine (NAC) uptake. The feasibility of detecting NAC-induced glutathione (GSH) biosynthesis using CEST MRI was also investigated. The detectability of the GSH amide and NAC thiol CEST effect at B0 = 7 T was determined in phantom experiments and simulations. C57BL/6 mice were injected intravenously (IV) with 50 g L−1 NAC in PBS (pH 7) during MRI acquisition. The dynamic magnetisation transfer ratio (MTR) and partial Z-spectral data were generated from the acquisition of measurements of the upfield NAC thiol and downfield GSH amide CEST effects in the liver. The 1H-NMR spectroscopy on aqueous mouse liver extracts, post-NAC-injection, was performed to verify hepatic NAC uptake. The dynamic MTR and partial Z-spectral data revealed a significant attenuation of the mouse liver MR signal when a saturation pulse was applied at −2.7 ppm (i.e., NAC thiol proton resonance) after the IV injection of the NAC solution. The 1H-NMR data revealed the presence of hepatic NAC, which coincided strongly with the increased upfield MTR in the dynamic CEST data, providing strong evidence that hepatic NAC uptake was detected. However, this MTR enhancement was attributed to a combination of NAC thiol CEST and some other upfield MT-generating mechanism(s) to be identified in future studies. The detection of hepatic GSH via its amide CEST MRI contrast was inconclusive based on the current results.

Regular Acetaminophen Use and Blood Pressure in People With Hypertension: The PATH-BP Trial

BACKGROUND

Acetaminophen is widely used as first-line therapy for chronic pain because of its perceived safety and the assumption that, unlike nonsteroidal anti-inflammatory drugs, it has little or no effect on blood pressure (BP). Although observational studies suggest that acetaminophen may increase BP, clinical trials are lacking. We, therefore, studied the effects of regular acetaminophen dosing on BP in individuals with hypertension.

METHODS

In this double-blind, placebo-controlled, crossover study, 110 individuals were randomized to receive 1 g acetaminophen 4× daily or matched placebo for 2 weeks followed by a 2-week washout period before crossing over to the alternate treatment. At the beginning and end of each treatment period, 24-hour ambulatory BPs were measured. The primary outcome was a comparison of the change in mean daytime systolic BP from baseline to end of treatment between the placebo and acetaminophen arms.

RESULTS

One-hundred three patients completed both arms of the study. Regular acetaminophen, compared with placebo, resulted in a significant increase in mean daytime systolic BP (132.8±10.5 to 136.5±10.1 mm Hg [acetaminophen] vs 133.9±10.3 to 132.5±9.9 mm Hg [placebo]; P<0.0001) with a placebo-corrected increase of 4.7 mm Hg (95% CI, 2.9-6.6) and mean daytime diastolic BP (81.2±8.0 to 82.1±7.8 mm Hg [acetaminophen] vs 81.7±7.9 to 80.9±7.8 mm Hg [placebo]; P=0.005) with a placebo-corrected increase of 1.6 mm Hg (95% CI, 0.5-2.7). Similar findings were seen for 24-hour ambulatory and clinic BPs.

CONCLUSIONS

Regular daily intake of 4 g acetaminophen increases systolic BP in individuals with hypertension by ≈5 mm Hg when compared with placebo; this increases cardiovascular risk and calls into question the safety of regular acetaminophen use in this situation. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT01997112. URL: https://www.clinicaltrialsregister.eu; Unique identifier: 2013-003204-40.

Fifteen-minute update: International normalised ratio as the treatment end point in children with acute paracetamol poisoning

Paracetamol is one of the most frequent reasons for poisonings across the UK with an estimated 90,000 patients and 150 deaths annually. International normalised ratio (INR) may be elevated due to hepatocellular damage and is frequently used to monitor progress on N-acetyl cysteine. N-acetyl cysteine is associated with reduced activity of vitamin K dependent clotting factors leading to a benign elevation of INR. In asymptomatic children with normal aspartate transaminase/alanine transaminase, isolated borderline elevation of INR following paracetamol overdose should be reviewed for possible N-acetyl cysteine induced elevation of INR. Due to these factors, in those with borderline persistent elevation of INR, N-acetyl cysteine can be safety stopped if INR is falling on two or more consecutive tests and is <3.0.

Acetaminophen Poisoning

Acetaminophen is a common medication taken in deliberate self-poisoning and unintentional overdose. It is the commonest cause of severe acute liver injury in Western countries. The optimal management of most acetaminophen poisonings is usually straightforward. Patients who present early should be offered activated charcoal and those at risk of acute liver injury should receive acetylcysteine. This approach ensures survival in most. The acetaminophen nomogram is used to assess the need for treatment in acute immediate-release overdoses with a known time of ingestion. However, scenarios that require different management pathways include modified-release, large/massive, and repeated supratherapeutic ingestions.

A two-bag acetylcysteine regimen is associated with shorter delays and interruptions in the treatment of paracetamol overdose

BACKGROUND

The three-bag intravenous (IV) acetylcysteine regimen for paracetamol overdose is associated with frequent and long delays during treatment. This has not been previously studied in regard to the two-bag regimen.

AIMS

Our primary aim was to compare the cumulative duration of delays during IV acetylcysteine infusion between the three-bag and two-bag regimens. Secondary aims were to compare the frequency of delays and to identify causes for delay.

METHODS

This was a retrospective cohort study of patients receiving IV acetylcysteine for the treatment of paracetamol overdose, conducted at three Australian emergency departments. A cohort of patients treated with the three-bag regimen from October 2009 to October 2013 was compared to patients treated with the two-bag regimen from February 2014 to May 2020. Start times of each infusion were sourced from medical records and delays were calculated by comparing actual infusion time against prescribed time. Evidence of adverse drug reactions - gastrointestinal reactions and cutaneous and systemic non-allergic anaphylactoid reactions (NAARs) - were also recorded.

RESULTS

The three-bag cohort included 271 cases and the two-bag cohort included 598 cases. Delays were significantly shorter in the two-bag cohort, compared to the three-bag cohort: median delay 35 min (IQR: 15, 70) vs 65 min (IQR: 40, 105), p < 0.01. Delays longer than 1 h were less frequent in the two-bag cohort: 31% vs 51%, p < 0.01. NAARs were associated with significantly longer delays in both cohorts and were more frequent in the three-bag cohort.

CONCLUSIONS

The two-bag regimen was associated with significantly fewer and shorter delays. NAARs, which were more frequent in the three-bag cohort, were associated with significantly longer delays.

Risk Factors for Hepatotoxicity Due to Paracetamol Overdose in Adults

Background and Objectives: Over-the-counter availability and a good safety profile make paracetamol one of the most common analgesics in developed countries but also the leading cause of liver failure due to overdose. The objectives of the study were to identify modifiable risk factors for severe hepatotoxicity following paracetamol overdose in adults. Materials and Methods: A retrospective cohort study involved the consecutive adult patients hospitalized in a toxicological center over a period of seven years due to paracetamol overdose. Complete medical datasets of laboratory and anamnestic variables were analyzed and validated by means of logistic regression model. Results: A total of 185 patients entered the study, including 25 individuals who developed severe hepatotoxicity (plasma aminotransferases levels above 1000 UI/L) and 31 individuals with mild to moderate liver injury (plasma aminotransferases levels above upper normal range, but below 1000 UI/L). In the univariable analysis, significant hepatotoxicity risk factors were male gender, alcohol abuse, an ingested paracetamol dose, and a timespan from ingestion to hospital admission. The later one was the only significant risk factor in the multivariable model (adjusted odds ratio 1.08; 95% CI: 1.03-1.12). Conclusions: A delay in hospital admission, resulting in a delayed administration of disease-specific treatment outweighs any other known risk factors of paracetamol-induced hepatotoxicity.

A metabolomic analysis of thiol response for standard and modified N-acetyl cysteine treatment regimens in patients with acetaminophen overdose

N-acetylcysteine (NAC) is an antidote to prevent acetaminophen (paracetamol-APAP)-induced acute liver injury (ALI). The 3-bag licensed 20.25 h standard regimen, and a 12 h modified regimen, are used to treat APAP overdose. This study evaluated the redox thiol response and APAP metabolites, in patients with a single APAP overdose treated with either the 20.25 h standard or 12 h modified regimen. We used liquid chromatography tandem mass spectrometry to quantify clinically important oxidative stress biomarkers and APAP metabolites in plasma samples from 45 patients who participated in a randomized controlled trial (SNAP trial). We investigated the time course response of plasma metabolites at predose, 12 h, and 20.25 h post-start of NAC infusion. The results showed that the 12 h modified regimen resulted in a significant elevation of plasma NAC and cysteine concentrations at 12 h post-infusion. We found no significant alteration in the metabolism of APAP, mitochondrial, amino acids, and other thiol biomarkers with the two regimens. We examined APAP and purine metabolism in overdose patients who developed ALI. We showed the major APAP-metabolites and xanthine were significantly higher in patients with ALI. These biomarkers correlated well with alanine aminotransferase activity at admission. Receiver operating characteristic analysis showed that at admission, plasma APAP-metabolites and xanthine concentrations were predictive for ALI. In conclusion, a significantly higher redox thiol response with the modified NAC regimen at 12 h postdose suggests this regimen may produce greater antioxidant efficacy. At baseline, plasma APAP and purine metabolites may be useful biomarkers for early prediction of APAP-induced ALI.

A review of alternative intravenous acetylcysteine regimens for acetaminophen overdose

INTRODUCTION

Acetylcysteine is the standard treatment for preventing hepatotoxicity caused by acetaminophen overdose. Several novel approaches to the management of acetaminophen overdose have been suggested to improve patient safety by reducing adverse drug reactions and dosing errors. This article reviews these alternative treatment regimens and intends to offer a detailed assessment of the available options to assist providers in managing cases of acetaminophen overdose.

AREAS COVERED

This review article covers observational and experimental studies that assessed the efficacy and safety of alternative intravenous acetylcysteine regimens for acetaminophen overdose. A literature search was conducted using PubMed, ProQuest, and Scopus to identify the studies, which included results through April 2021. The assessment of alternative regimens consists of a discussion on the limitations and benefits, barriers to implementation, and important considerations for each regimen.

EXPERT OPINION

Several alternative regimens have been studied and implemented in various institutions. Many of these dosing regimens have supporting safety data but most lack robust data. A reduction in infusion-related side effects is an important outcome, but established efficacy, local poison center familiarity with the regimen, institutional resources, and patient-specific factors should be equally considered when deciding on implementing and using an alternative dosing strategy.

N-acetylcysteine, xCT and suppression of Maxi-chloride channel activity in human placenta

INTRODUCTION

Placental oxidative stress features in pregnancy pathologies but in clinical trials antioxidant supplementation has not improved outcomes. N-acetylcysteine (NAC) stimulates glutathione production and is proposed as a therapeutic agent in pregnancy. However, key elements of N-acetylcysteine biology, including its cellular uptake mechanism, remains unclear. This study explores how the cystine/glutamate transporter xCT may mediate N-acetylcysteine uptake and how N-acetylcysteine alters placental redox status.

METHODS

The involvement of xCT in NAC uptake by the human placenta was studied in perfused placenta and Xenopus oocytes. The effect of short-term N-acetylcysteine exposure on the placental villous proteome was determined using LC-MS. The effect of N-acetylcysteine on Maxi-chloride channel activity was investigated in perfused placenta, villous fragments and cell culture.

RESULTS

Maternoplacental N-acetylcysteine administration stimulated intracellular glutamate efflux suggesting a role of the exchange transporter xCT, which was localised to the microvillous membrane of the placental syncytiotrophoblast. Placental exposure to a bolus of N-acetylcysteine inhibited subsequent activation of the redox sensitive Maxi-chloride channel independently of glutathione synthesis. Stable isotope quantitative proteomics of placental villi treated with N-acetylcysteine demonstrated changes in pathways associated with oxidative stress, apoptosis and the acute phase response.

DISCUSSION

This study suggests that xCT mediates N-acetylcysteine uptake into the placenta and that N-acetylcysteine treatment of placental tissue alters the placental proteome while regulating the redox sensitive Maxi-chloride channel. Interestingly N-acetylcysteine had antioxidant effects independent of the glutathione pathway. Effective placental antioxidant therapy in pregnancy may require maintaining the balance between normalising redox status without inhibiting physiological redox signalling.

Acute liver failure

Acute liver failure is a rare syndrome and is primarily caused by paracetamol toxicity in developed nations. Survival for patients with acute liver failure has steadily improved over the last few decades from approximately 20% to greater than 60%. This marked improvement in survival has been due to a combination of improvements in medical practice and the use of emergency liver transplantation in selected patients. Early recognition and timely initial management in the non-specialist centre can significantly improve outcomes. Patients should be simultaneously discussed with a transplant centre and referred to critical care. Close liaison with transplant centres to ensure timely transfer in deteriorating patients is important.

​False-positive paracetamol levels in a patient with hyperbilirubinaemia: clinical perspectives

​Serum concentrations of paracetamol are measured to investigate the cause of acute hepatitis, monitor the clearance of paracetamol from the body and to determine if supratherapeutic levels warrant treatment with N-acetylcysteine (NAC). ​A 49-year-old man treated for ischaemic colitis developed worsening renal and liver function tests. As part of the investigation of hepatorenal failure, paracetamol levels were requested, which were elevated at 14 mg/L (normal <4 mg/L) resulting in treatment with NAC. Despite treatment, levels of paracetamol remained elevated and the link between hyperbilirubinemia and false-positive paracetamol levels was identified. ​Bilirubin and its by-products have intense absorbance in the ultraviolet and visible regions of the electromagnetic spectrum, causing interference in the enzymatic colorimetric assay most commonly used to measure paracetamol concentration, resulting in false-positive paracetamol levels. Laboratories correct for this interference above a predetermined bilirubin concentration, termed the Icteric Index; however, in our case this interference occurred at a lower level of hyperbilirubinaemia than previously identified as significant. This interaction was found to be more significant at lower bilirubin levels when low or no paracetamol levels were present in the serum, resulting in a change to laboratory practice and development of a ‘Sliding Scale’ approach to analysis. ​Concurrent bilirubin or Icteric Index measurement is recommended for all laboratories that use the enzymatic colorimetric assay for paracetamol measurement. Lower Icteric Index or bilirubin thresholds are required when low or no paracetamol levels are present in the serum to prevent false-positive paracetamol results. We describe a new ‘Sliding Scale’ approach to analysis, and highlight an important interaction for clinicians to be aware of.

Efficacy of a two bag acetylcysteine regimen to treat paracetamol overdose (2NAC study)

BACKGROUND

Previous studies of paracetamol overdose treatment show that a 2-bag, 20-h intravenous (IV) acetylcysteine regimen decreased the incidence of non-allergic anaphylactic reactions compared to the 3-bag, 21 h IV regimen, but have not examined efficacy of the 20-h 2 bag regimen.

METHODS

This was a multi-centre observational study of paracetamol overdose presentations treated with a 2-bag IV acetylcysteine regimen (200 mg/kg over 4 h, 100 mg/kg over 16 h) compared to a 3-bag regimen, performed from 2009 to 2019. Patients were referred from the emergency department to the inpatient toxicology units for continued management. For the primary non-inferiority analysis: subjects had single, acute ingestions, a serum paracetamol-concentration performed 4 to 8-h post-ingestion. The primary outcome was development of acute liver injury (ALI), defined as peak ALT>150 U/L; and > double admission baseline ALT (for presentations within 24 h post-overdose). Secondary outcomes included adverse reactions to acetylcysteine (cutaneous and systemic).

FINDING

Out of 6419 paracetamol overdoses, 2763 received acetylcysteine. For the primary analysis, 1003 received the 2-bag and 783 the 3-bag acetylcysteine regimen. When presentation bloods were performed 4 to 8-h post-overdose, 21 (3.1%) developed ALI with the 2-bag regimen vs 16 (2.9%) with the 3-bag regimen (Difference: 0.2%, 95%CI:-1.6 to 2.2). The incidence of hepatotoxicity was: 1.2% (n = 8) with the two-bag regimen and 1.6% (n = 9) with the three-bag regimen (Difference -0.4%, 95%CI -1.75, 0.91). When presentation bloods were performed 8 to 24-h post-overdose, 70 (21%) developed ALI with the 2-bag regimen vs 46 (23%) with the 3-bag regimen (Difference: -2%, 95%CI -9.12 to 5.36). There were significantly less cutaneous and systemic non-allergic anaphylactic reactions recorded after treatment with the two-bag than the three-bag regimen (1.3% [n = 17] and 7.1% [n = 65], Difference: -5.8%, 95%CI -7.6 to -4.0, p < 0.0001), respectively.

INTERPRETATION

A two-bag intravenous acetylcysteine regimen was found to be non-inferior to the three-bag regimen with regards to efficacy in preventing acute liver injury for early presentations of paracetamol overdose. No important differences were seen for any other presentations. The two-bag regimen also decreased the incidence of both non-allergic anaphylactic reactions and gastrointestinal adverse events from acetylcysteine treatment.

FUNDING

AW is funded by a National Health and Medical Research Council (NHMRC) Early Career Fellowship ID 1159907. GI is funded by a NHMRC Senior Research Fellowship ID 1061041. The NHMRC had no role in the design, writing of this manuscript. The corresponding author (AW) had full access to all the data in the study and final responsibility for the decision to submit the manuscript for publication.

Direct Detection of miR-122 in Hepatotoxicity Using Dynamic Chemical Labeling Overcomes Stability and isomiR Challenges

Circulating microRNAs are biomarkers reported to be stable and translational across species. MicroRNA-122 (miR-122) is a hepatocyte-specific microRNA biomarker for drug-induced liver injury (DILI). We developed a single molecule, dynamic chemical labeling (DCL) assay to directly detect miR-122 in blood. The DCL assay specifically measured miR-122 directly from 10 μL of serum or plasma without any extraction steps, with a limit of detection of 1.32 pM that enabled the identification of DILI. Testing of 192 human serum samples showed that DCL accurately identified patients at risk of DILI after acetaminophen overdose (area under ROC curve 0.98 (95% CI; 0.96-1), P < 0.0001). The DCL assay also identified liver injury in rats and dogs. The use of specific captured beads had the additional benefit of stabilizing miR-122 after sample collection, with no signal loss after 14 days at room temperature, in contrast to PCR that showed significant loss of signal. RNA sequencing demonstrated the presence of multiple miR-122 isomiRs in the serum of patients with DILI that were at low concentration or not present in healthy individuals. Sample degradation over time produced more isomiRs, particularly rapidly with DILI. PCR was inaccurate when analyzing miR-122 isomiRs, whereas the DCL assay demonstrated accurate quantification. We conclude that the DCL assay can accurately measure miR-122 to diagnose liver injury in humans and other species and can overcome microRNA stability and isomiR challenges.

Adducts Post Acetaminophen Overdose Treated with a 12-Hour vs 20-Hour Acetylcysteine Infusion

INTRODUCTION

Acetaminophen protein adducts in the circulation are a specific biomarker of acetaminophen oxidation, and may be a more sensitive measure of impending hepatic injury following overdose than alanine transaminase (ALT). We performed an exploratory analytical substudy of adducts during a clinical trial (NACSTOP) of abbreviated (12-hour) versus control (20-hour) acetylcysteine to identify any signal of diminished antidotal effectiveness with shortened therapy.

METHODS

We measured adducts at 0, 12, and 20 hours from a convenience sample of subjects enrolled in the cluster-controlled NACSTOP trial evaluating a 12-hour ("abbreviated"; 200 mg/kg over 4 hours, 50 mg/kg over 8 hours) vs 20-hour acetylcysteine regimen ("control"; 200 mg/kg over 4 hours, 100 mg/kg over 16 hours). Adducts were assayed using high-performance liquid chromatography/mass spectrometry.

RESULTS

Median ALT 20 hours after the initiation of acetylcysteine was 12 U/L (IQR 8,14) in the abbreviated 12-hour regimen group (N = 8), compared with the control group 16 U/L (IQR 11,21; N = 21) (p = 0.46). Adduct concentrations were similarly low in both groups: abbreviated [(0.005 μmol/L, IQR (0,0.14)] and control [(0.005 μmol/L, IQR (0,0.05)] (p = 0.61).

CONCLUSIONS

There were minimal to no acetaminophen protein adducts detected. These findings further support discontinuing acetylcysteine when acetaminophen concentrations are low and liver function tests normal after 12 hours of treatment.

Pharmacokinetic profile of N-acetylcysteine amide and its main metabolite in mice using new analytical method

N-acetylcysteine amide (NACA) is the amide derivative of N-acetylcysteine (NAC) that is rapidly converted to NAC after systemic administration. It has emerged as a promising thiol antioxidant for multiple indications; however, the pharmacokinetic property is yet unclear due to lack of an accurate quantification method. The present investigation aimed to develop an analytical method for simultaneous quantification of NACA and NAC in plasma. A new reagent (2-(methylsulfonyl)-5-phenyl-1,3,4-oxadiazole, MPOZ) was introduced for thiol stabilization during sample processing and storage. Further, we utilized tris (2-carboxyethyl) phosphine (TCEP) to reduce the oxidized forms of NACA and NAC. After derivatization, NACA-MPOZ and NAC-MPOZ were quantified using liquid chromatography-mass spectrometry (LC-MS). The new method was validated and found to have high specificity, linearity, accuracy, precision, and recovery for the quantification of NACA and NAC in plasma. Furthermore, the formed derivatives of NACA and NAC were stable for 48 h under different conditions. The method was utilized in pharmacokinetic study which showed that the bioavailability of NACA is significantly higher than NAC (67% and 15%, respectively). The pharmacokinetic of NACA obeyed a two-compartment open model. The glutathione (GSH)-replenishing capacity was found to be three to four-fold higher after the administration of NACA compared to that observed after the administration of NAC. In conclusion, the present method is simple, robust and reproducible, and can be utilized in both experimental and clinical studies. NACA might be considered as a prodrug for NAC. Furthermore, this is the first report describing the pharmacokinetics and bioavailability of NACA in mouse.

Two-bag intravenous N-acetylcysteine, antihistamine pretreatment and high plasma paracetamol levels are associated with a lower incidence of anaphylactoid reactions to N-acetylcysteine

Context: N-acetylcysteine (NAC) is used worldwide to prevent liver injury after paracetamol overdoses. Anaphylactoid reactions to NAC occur frequently and often lead to treatment interruptions or discontinuations. In Denmark in 2013, the NAC treatment regimen was simplified from a three-bag to a two-bag NAC regimen. Factors of importance for the development of anaphylactoid reaction to this new regimen are poorly explored. Previous studies have suggested a protective effect of high plasma levels of paracetamol on the development of anaphylactoid reactions. Likewise, exposure to antihistamines prior to NAC treatment may protect against these reactions.Methods: This is a retrospective cohort study of patients treated with NAC and with at least one plasma paracetamol sample performed in the Capital Region of Denmark from 2010 to 2017. The primary outcome was the incidence of anaphylactoid reactions to NAC requiring intravenous treatment with antihistamines and/or glucocorticoids. Logistic regression analyses were carried out to identify the risk of developing an anaphylactoid reaction to NAC affected by influencing factors.Results: Of 4315 admissions included in the study, 259 (6.0%) developed an anaphylactoid reaction to NAC. The two-bag regimen (adjusted OR 0.44 [95%CI: 0.32-0.60]), increasing age (adjusted OR 0.84 [95%CI: 0.78-0.90] per 10-year increase) or children <10 years (adjusted OR 0.14 [95%CI: 0.04-0.36]) and antihistamine co-ingestion in overdose (adjusted OR 0.17 [95%CI: 0.02-0.64]) were associated with significantly fewer anaphylactoid reactions. High plasma paracetamol concentrations protected against development of anaphylactoid reactions during the two-bag regimen (adjusted OR 0.59 [95%CI: 0.47-0.71] and three-bag regimen 0.82 [95%CI: 0.72-0.94] per doubling of paracetamol concentration). The effect differed between the two regimens (p = .004 for interaction).Conclusion: In this retrospective cohort, a high peak plasma paracetamol concentration, age, antihistamine co-ingestion and use of the two-bag NAC regimen were associated with fewer anaphylactoid reactions to NAC.

Reply to the ‘Comment on “Acetylcysteine in paracetamol poisoning: a perspective of 45 years of use”’ by M. E. Mullins, M. C. Yarema, M. L. A. Sivilotti, M. Thompson, D. A. Algren, M. C. Beuhler and C. P. Holstege, Toxicol. Res., 2019, 8, DOI: 10.1039/C9TX00158A

Mullins et al. made a comment on our article (DOI: ; 10.1039/C9TX00002J) stating they noticed the omission of the one-bag, standard concentration protocol which is shared by several centers in North America when we discussed IV acetylcysteine protocols. In this reply we clarify that we did not include this methodology as it is a technical adaption of the way in which a 2-bag NAC regimen in administered and there is insufficient comparative data with other regimens.

Principal results of a randomised open label exploratory, safety and tolerability study with calmangafodipir in patients treated with a 12 h regimen of N-acetylcysteine for paracetamol overdose (POP trial)

Background

The POP Trial was a phase 1, open-label, rising-dose, randomised study that explored the safety and tolerability of calmangafodipir (superoxide dismutase mimetic) co-treatment with n-acetylcysteine (NAC) for paracetamol overdose.

Methods

Patients were recruited at the Royal Infirmary of Edinburgh (8th June 2017-10th May 2018). Inclusion criterion: adults within 24 h of a paracetamol overdose that required NAC. Within each of 3 sequential cohorts, participants were randomly assigned, with concealed allocation, to NAC and a single intravenous calmangafodipir dose (n = 6) or NAC alone (n = 2). Calmangafodipir doses were 2, 5, or 10 μmol/kg. Participants, study and clinical teams were not blinded. The primary outcome was safety and tolerability. Secondary outcomes were alanine transaminase (ALT), international normalised ratio (INR), keratin-18, caspase-cleaved keratin-18 (ccK18), microRNA-122, and glutamate dehydrogenase (GLDH). (Clinicaltrials.gov:NCT03177395).

Findings

All 24 participants received their allocated drug doses and were analysed. Primary endpoints: all participants experienced ≥1 adverse event (AE), most commonly gastrointestinal. Patients experiencing ≥1 serious adverse event (SAE): NAC alone, 2/6; NAC + calmangafodipir (2 μmol/kg), 4/6; NAC + calmangafodipir (5 μmol/kg), 2/6; NAC + calmangafodipir (10 μmol/kg), 3/6. No AEs or SAEs were probably or definitely calmangafodipir-related. Secondary safety outcomes demonstrated no differences between groups. With NAC alone, 2/6 had ALT > 100 U/L; with NAC + calmangafodipir, 0/18. No INR difference. Keratin-18 and ccK18 increased in the NAC alone group more than with calmangafodipir (baseline to 20 h fold change, NAC + calmangafodipir (5 μmol/kg) compared to NAC alone: 0.48 (95%CI 0.28–0.83)). microRNA-122 changes were similar to K18, GLDH was frequently undetected.

Interpretation

Calmangafodipir was tolerated when combined with NAC and may reduce biomarkers of paracetamol toxicity.