Fewer adverse effects associated with a modified two-bag intravenous acetylcysteine protocol compared to traditional three-bag regimen in paracetamol overdose

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.

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.

Comparison of Two-Bag Versus Three-Bag N-Acetylcysteine Regimens for Pediatric Acetaminophen Toxicity

BACKGROUND

Acetaminophen overdose is a leading cause of liver failure, and a leading cause of pediatric poisoning requiring hospital admission. The antidote, N-acetylcysteine (NAC), is traditionally administered as a three-bag intravenous infusion. Despite its efficacy, NAC is associated with high incidence of nonallergic anaphylactoid reactions (NAARs). Adult evidence demonstrates that alternative dosing regimens decrease NAARs and medication errors (MEs).

OBJECTIVES

To compare NAARs and MEs associated with two- versus three-bag NAC for acetaminophen overdose in a pediatric population.

METHODS

This is a retrospective observational cohort study comparing pediatric patients who received three- versus two-bag NAC for acetaminophen toxicity. The primary outcome was incidence of NAARs. Secondary outcomes were rates of MEs and relevant hospital outcomes (length of stay [LOS], intensive care unit (ICU) admission, liver transplant, death).

RESULTS

Two hundred forty-three patients met inclusion criteria (median age of 15 years): 150 (62%) three-bag NAC and 93 (38%) two-bag NAC. There was no difference in overall NAARs (p = 0.54). Fewer cutaneous NAARs were observed in the two-bag group, three-bag: 15 (10%), two-bag: 2 (2%), p = 0.02. MEs were significantly decreased with the two-bag regimen, three-bag: 59 (39%), two-bag: 21 (23%), p = 0.01. No statistical differences were observed in LOS, ICU admissions, transplant, or death.

CONCLUSION AND RELEVANCE

A significant decrease in cutaneous NAARs and MEs was observed in pediatric patients by combining the first two bags of the traditional three-bag NAC regimen. In pediatric populations, a two-bag NAC regimen for acetaminophen overdose may improve medication tolerance and safety.

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.

Comparing development of liver injury using the two versus three bag acetylcysteine regimen despite early treatment in paracetamol overdose

INTRODUCTION

Some studies have reported that early administration of acetylcysteine using a 3-bag regimen may not fully prevent development of liver injury in some patients. We compared the incidence of acute liver injury (ALI) in patients receiving acetylcysteine within eight hours of ingestion between the two-bag acetylcysteine regimen (200 mg/kg over four hours, 100 mg/kg over 16 h) and the three-bag regimen (150 mg/kg over 1 h, 50 mg/kg over 4 h, 100 mg/kg over 16 h).

METHOD

This was a retrospective cohort study of the two-bag and three-bag acetylcysteine regimens from Monash Health, Victoria, Australia (2009-2020), compared to the three-bag acetylcysteine regimen data from the Canadian Acetaminophen Overdose Study (CAOS) database (1980-2005). The inclusion criteria included patients with an acute single ingestion of paracetamol; normal aminotransferases on presentation and acetylcysteine administered within eight hours post-overdose. The primary outcome was development of ALI (defined as: peak aminotransferase >150 IU/L).

RESULTS

At Monash Health, 191 patients were treated with the two-bag acetylcysteine regimen, and 180 patients with the three-bag regimen. The CAOS cohort provided 515 patients treated with the three-bag regimen. ALI developed in 1.6% (3/191) of the two-bag Monash Health group, 2.2% (4/180) of the three-bag Monash Health group (difference -0.6%, p 0.7), and 2.9% (15/515) of the three-bag CAOS group (difference compared to two-bag -1.3%, p 0.4). Hepatotoxicity (ALT >1000) developed in 0.5% (1/191) of patients treated with the two-bag regimen, 1.7% (3/180) in the Monash Health three-bag regimen and 1% (5/515) of the three-bag CAOS group. There were no statistically significant differences between groups.

CONCLUSIONS

ALI and hepatotoxicity were observed in a small, comparable percentage of patients despite early acetylcysteine administration using the two-bag and three-bag regimens. Repeating blood tests at the end of acetylcysteine treatment will identify these patients and indicate those requiring continuation of acetylcysteine.

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.

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.

Key articles and guidelines for the emergency medicine clinical pharmacist: 2011-2018 update

PURPOSE

To summarize recently published research reports and practice guidelines on emergency medicine (EM)-related pharmacotherapy.

SUMMARY

Our author group was composed of 14 EM pharmacists, who used a systematic process to determine main sections and topics for the update as well as pertinent literature for inclusion. Main sections and topics were determined using a modified Delphi method, author and peer reviewer groups were formed, and articles were selected based on a comprehensive literature review and several criteria for each author-reviewer pair. These criteria included the document "Oxford Centre for Evidence-based Medicine - Levels of Evidence (March 2009)" but also clinical implications, interest to reader, and belief that a publication was a "key article" for the practicing EM pharmacist. A total of 105 articles published from January 2011 through July 2018 were objectively selected for inclusion in this review. This was not intended as a complete representation of all available pertinent literature. The reviewed publications address the management of a wide variety of disease states and topic areas that are commonly found in the emergency department: analgesia and sedation, anticoagulation, cardiovascular emergencies, emergency preparedness, endocrine emergencies, infectious diseases, neurology, pharmacy services and patient safety, respiratory care, shock, substance abuse, toxicology, and trauma.

CONCLUSION

There are many important recent additions to the EM-related pharmacotherapy literature. As is evident with the surge of new studies, guidelines, and reviews in recent years, it is vital for the EM pharmacist to continue to stay current with advancing practice changes.

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.

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.

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.

The NACSTOP Trial: A Multicenter, Cluster-Controlled Trial of Early Cessation of Acetylcysteine in Acetaminophen Overdose

Historically, intravenous acetylcysteine has been delivered at a fixed dose and duration of 300 mg/kg over 20 to 21 hours to nearly every patient deemed to be at any risk for hepatotoxicity following acetaminophen overdose. We investigated a 12-hour treatment regimen for selected low-risk patients. This was a multicenter, open-label, cluster-controlled trial at six metropolitan emergency departments. We enrolled subjects following single or staggered acetaminophen overdose with normal serum alanine transaminase (ALT) and creatinine on presentation and at 12 hours, and less than 20 mg/L acetaminophen at 12 hours. Patients were allocated to intervention (250 mg/kg over 12-hour) or control (300 mg/kg over 20-hour) regimens by site. The primary outcome was incidence of "hepatic injury" 20 hours following initiation of acetylcysteine treatment, defined as ALT doubling and peak ALT greater than 100 IU/L, indicating the need for further antidotal treatment. Secondary outcomes included incidence of hepatotoxicity (ALT > 1,000 IU/L), peak international normalized ratio (INR), and adverse drug reactions. Of the 449 acetaminophen overdoses receiving acetylcysteine, 100 were recruited to the study. Time to acetylcysteine (median 7 hours [interquartile ratio 6,12] versus 7 hours [6,10]) and initial acetaminophen (124 mg/L [58,171] versus 146 mg/L [66,204]) were similar between intervention and control groups. There was no difference in ALT (18 IU/L [13,22] versus 16 IU/L [13,21]) or INR (1.2 versus 1.2) 20 hours after starting acetylcysteine between groups. No patients developed hepatic injury or hepatotoxicity in either group (odds ratio 1.0 [95% confidence interval 0.02, 50]). No patients represented with liver injury, none died, and 96 of 96 were well at 14-day telephone follow-up. Conclusion: Discontinuing acetylcysteine based on laboratory testing after 12 hours of treatment is feasible and likely safe in selected patients at very low risk of liver injury from acetaminophen overdose.

Paracetamol metabolite concentrations following low risk overdose treated with an abbreviated 12-h versus 20-h acetylcysteine infusion

CONTEXT

To compare degree of liver injury and paracetamol metabolite concentrations after treatment with standard of care (20-h) vs. abbreviated (12-h) acetylcysteine regimens used in paracetamol overdose (NACSTOP trial).

METHODS

Timed blood samples from a cohort of subjects enrolled in the cluster-controlled NACSTOP trial evaluating a 12-h acetylcysteine regimen (200 mg/kg over 4 h, 50 mg/kg over 8 h) were assayed for paracetamol metabolites as a pilot study, using liquid chromatography/mass spectrometry. Control group subjects received a 20-h course of acetylcysteine (200 mg/kg over 4 h, 100 mg/kg over 16 h). The intervention group received a 12-h acetylcysteine regimen (stopped after at least 12 h of treatment). Positive control groups not in the trial with acute liver injury (ALI) or hepatotoxicity were also studied.

RESULTS

One hundred and forty-one blood samples were collected from 40 patients receiving acetylcysteine after paracetamol overdose. Median ALT after 20 h of acetylcysteine was 12 U/L (IQR 8.14) in the abbreviated regimen group, compared to the control group 16 U/L (IQR 11.21) (p = .46). There was no significant difference in median metabolite concentrations on presentation and after 20 h of acetylcysteine between these two groups (p > .05). Presentation median sum CYP-metabolite/total metabolite percentages were 2.5 and 3.0 in the abbreviated and control NACSTOP groups, respectively.

CONCLUSIONS

An abbreviated 12-h acetylcysteine regimen for paracetamol overdose used in the NACSTOP trial had similar circulating metabolite concentrations compared to a 20-h regimen in selected subjects with low risk of hepatotoxicity. This suggests that further acetylcysteine may not be needed in the abbreviated group at time of cessation.