A New Predictor of Toxicity Following Acetaminophen Overdose Based on Pretreatment Exposure

The Evolution of Circulating Biomarkers for Use in Acetaminophen/Paracetamol-Induced Liver Injury in Humans: A Scoping Review

Acetaminophen (APAP) is a widely used drug, but overdose can cause severe acute liver injury. The first reports of APAP hepatotoxicity in humans were published in 1966, shortly after the development of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) as the first biomarkers of liver injury as opposed to liver function. Thus, the field of liver injury biomarkers has evolved alongside the growth in APAP hepatotoxicity incidence. Numerous biomarkers have been proposed for use in the management of APAP overdose patients in the intervening years. Here, we comprehensively review the development of these markers from the 1960s to the present day and briefly discuss possible future directions.

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.

Acetylcysteine in paracetamol poisoning: a perspective of 45 years of use

Paracetamol poisoning was first reported in 1966. The development of antidotes followed within 10 years, and by 1980 acetylcysteine (NAC) was acknowledged as the optimal therapy available. This article examines the history of the development of NAC and recent developments in its use. We offer suggestions for improvements in the way NAC may be administered and outline new developments that should have major impacts on the way we manage paracetamol poisoning in the near future.

Outcomes of Patients With Premature Discontinuation of the 21-h Intravenous N-Acetylcysteine Protocol After Acute Acetaminophen Overdose

BACKGROUND

The minimum recommended treatment duration for i.v. N-acetylcysteine (NAC) after an acute, single acetaminophen (APAP) overdose is 21 h. Some have questioned whether shorter courses may be sufficient in carefully selected cases.

OBJECTIVE

We sought to describe the incidence of hepatotoxicity in a cohort of acute APAP overdose patients who received <21 h of i.v. NAC for any reason.

METHODS

We performed a secondary analysis of a large multicenter retrospective cohort of patients hospitalized for APAP poisoning. We selected patients with a potentially toxic serum APAP concentration measured between 4 and 24 h post ingestion, in whom i.v. NAC was initiated but discontinued before completing the full 21-h course. We further characterized outcomes in these patients as a function of two novel risk-prediction tools, the psi (ψ) parameter and APAP × aminotransferase (AT) product. The ψ parameter is an estimate of the cellular burden of injury based on the area under the concentration-time curve before treatment, and calculated with respect to the APAP concentration and time to initiation of NAC.

RESULTS

Fifty-nine patients met inclusion criteria. Intravenous NAC was initiated a median of 11.3 h post ingestion and administered for a median of 11.0 h. Hepatotoxicity (aspartate aminotransferase [AST] or alanine aminotransferase [ALT] > 1,000 IU/L) occurred in one patient (1.7%; 95% confidence interval 0.04-9.1), and eight additional patients developed hepatic injury (AST or ALT > 100 IU/L). No fatalities occurred. A multiplication product of APAP and AT (APAP × AT) that falls below 10,000 μmol/L/IU-L, or pretreatment ψ < 5 mmol/L-h suggested a low risk of hepatic injury.

CONCLUSIONS

In this retrospective analysis of patients treated with < 21 h of i.v. NAC for acute APAP overdose, the incidence of hepatotoxicity and coagulopathy was low, despite delays to NAC treatment.

Paracetamol poisoning: beyond the nomogram

Paracetamol poisoning is the commonest overdose seen in the UK. The management of patients with paracetamol poisoning has been little changed for the past 40 years, with a weight related dose of antidote (acetylcysteine) and treatment based on nomograms relating paracetamol concentration to time from ingestion. In 2012 the UK Commission on Human Medicines recommended a revision of the nomogram, following the death of a young woman, lowering the treatment threshold for all patients. As a result many more patients were treated. This has resulted in a large increase in admissions and in the proportion suffering adverse reactions to the antidote acetylcysteine since, interestingly, higher paracetamol concentrations inhibit anaphylactoid reactions to the antidote. New approaches to assessing the toxicity of paracetamol are now emerging using new biomarkers in blood. This article discusses new approaches to risk assessment and treatment for paracetamol overdose based on recent research in this area.

Extracorporeal treatment for acetaminophen poisoning: recommendations from the EXTRIP workgroup

BACKGROUND

The Extracorporeal Treatments in Poisoning (EXTRIP) workgroup was created to provide evidence-based recommendations on the use of extracorporeal treatments (ECTR) in poisoning and the results are presented here for acetaminophen (APAP).

METHODS

After a systematic review of the literature, a subgroup selected and reviewed the articles and summarized clinical and toxicokinetic data in order to propose structured voting statements following a pre-determined format. A two-round modified Delphi method was chosen to reach a consensus on voting statements, and the RAND/UCLA Appropriateness Method was used to quantify disagreement. Following discussion, a second vote determined the final recommendations.

RESULTS

Twenty-four articles (1 randomized controlled trial, 1 observational study, 2 pharmacokinetic studies, and 20 case reports or case series) were identified, yielding an overall very low quality of evidence for all recommendations. Clinical data on 135 patients and toxicokinetic data on 54 patients were analyzed. Twenty-three fatalities were reviewed. The workgroup agreed that N-acetylcysteine (NAC) is the mainstay of treatment, and that ECTR is not warranted in most cases of APAP poisoning. However, given that APAP is dialyzable, the workgroup agreed that ECTR is suggested in patients with excessively large overdoses who display features of mitochondrial dysfunction. This is reflected by early development of altered mental status and severe metabolic acidosis prior to the onset of hepatic failure. Specific recommendations for ECTR include an APAP concentration over 1000 mg/L if NAC is not administered (1D), signs of mitochondrial dysfunction and an APAP concentration over 700 mg/L (4630 mmol/L) if NAC is not administered (1D) and signs of mitochondrial dysfunction and an APAP concentration over 900 mg/L (5960 mmol/L) if NAC is administered (1D). Intermittent hemodialysis (HD) is the preferred ECTR modality in APAP poisoning (1D).

CONCLUSION

APAP is amenable to extracorporeal removal. Due to the efficacy of NAC, ECTR is reserved for rare situations when the efficacy of NAC has not been definitively demonstrated.

[Severe toxic acute liver failure: etiology and treatment]

Many substances, drugs or not, can be responsible for acute hepatitis. Nevertheless, toxic etiology, except when that is obvious like in acetaminophen overdose, is a diagnosis of elimination. Major causes, in particular viral etiologies, must be ruled out. Acetaminophen, antibiotics, antiepileptics and antituberculous drugs are the first causes of drug-induced liver injury. Severity assessment of the acute hepatitis is critical. Acute liver failure (ALF) is defined by the factor V, respectively more than 50% for the mild ALF and less than 50% for the severe ALF. Neurological examination must be extensive to the search for encephalopathy signs. According to the French classification, fulminant hepatitis is defined by the presence of an encephalopathy in the two first weeks and subfulminant between the second and 12th week after the advent of the jaundice. During acetaminophen overdose, with or without hepatitis or ALF, intravenous N-acetylcysteine must be administered as soon as possible. In the non-acetaminophen related ALF, N-acetylcysteine improves transplantation-free survival. Referral and assessment in a liver transplantation unit should be discussed as soon as possible.

Mathematical modeling of liver injury and dysfunction after acetaminophen overdose: early discrimination between survival and death

Acetaminophen (APAP) is the leading cause of acute liver injury in the developed world. Timely administration of N-acetylcysteine (N-Ac) prevents the progression of serious liver injury and disease, whereas failure to administer N-Ac within a critical time frame allows disease progression and in the most severe cases may result in liver failure or death. In this situation, liver transplantation may be the only life-saving measure. Thus, the outcome of an APAP overdose depends on the size of the overdose and the time to first administration of N-Ac. We developed a system of differential equations to describe acute liver injury due to APAP overdose. The Model for Acetaminophen-induced Liver Damage (MALD) uses a patient's aspartate aminotransferase (AST), alanine aminotransferase (ALT), and international normalized ratio (INR) measurements on admission to estimate overdose amount, time elapsed since overdose, and outcome. The mathematical model was then tested on 53 patients from the University of Utah. With the addition of serum creatinine, eventual death was predicted with 100% sensitivity, 91% specificity, 67% positive predictive value (PPV), and 100% negative predictive value (NPV) in this retrospective study. Using only initial AST, ALT, and INR measurements, the model accurately predicted subsequent laboratory values for the majority of individual patients. This is the first dynamical rather than statistical approach to determine poor prognosis in patients with life-threatening liver disease due to APAP overdose.

CONCLUSION

MALD provides a method to estimate overdose amount, time elapsed since overdose, and outcome from patient laboratory values commonly available on admission in cases of acute liver failure due to APAP overdose and should be validated in multicenter prospective evaluation.

Toxicodynamics of subacute co-exposure to groundwater contaminant arsenic and analgesic-antipyretic drug acetaminophen in rats

Arsenic is an environmental contaminant, while acetaminophen is an extensively used nonsteroidal analgesic-antipyretic drug. We evaluated whether subacute co-exposure to arsenic and acetaminophen would produce more toxicity than that caused by exposure to either of the xenobiotics in rats. Toxicity was evaluated through changes in body weight, feed consumption, liver weight and microsomal drug-metabolizing enzymes, lipid peroxidation and antioxidants in liver. Arsenic had no effect on body weight and feed consumption. Acetaminophen-mediated decrease in body weight was attenuated in the co-exposed rats. Acetaminophen alone or its co-administration with arsenic decreased feed consumption. Arsenic reduced acetaminophen-mediated increase in the activities of drug-metabolizing enzymes. The co-exposure caused lesser lipid peroxidation than the individual exposure. Arsenic or acetaminophen given alone depleted GSH and decreased the activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase and glutathione-S-transferase and these effects remained mostly unaffected after co-exposure. The results suggest that co-exposure to arsenic and acetaminophen may be less hazardous than their independent exposure in rats.

Estimated risk of hepatotoxicity after an acute acetaminophen overdose in alcoholics

A published logistic regression model based on the Canadian Acetaminophen Overdose Study registry was used to calculate the risk of hepatotoxicity after an acute acetaminophen overdose and to estimate a treatment threshold line for alcoholic patients who did not co-ingest alcohol (i.e., abstinent alcoholics) on the Rumack-Matthew nomogram. The risk of hepatotoxicity in nonalcoholic and abstinent alcoholic patients was calculated at the acetaminophen concentration of 150 microg/ml at 4h (37.5 microg/ml at 12h) treatment threshold line. This corresponds to the "possible risk" line on the Rumack-Matthew nomogram and represents a 1.6% risk of hepatotoxicity for nonalcoholic patients at or below this line. At or below this same 150 microg/ml at 4-h line, abstinent alcoholic patients have a hepatotoxicity risk of 10.7%. The risk of hepatotoxicity in abstinent alcoholics' equivalent to that of nonalcoholics (i.e., 1.6%) occurs at a lower acetaminophen concentrations treatment threshold line, that is, 104 microg/ml at 4h (26 microg/ml at 12h). Because of difficulties plotting this new line on the familiar Rumack-Matthew semilogarithmic scale, a line connecting 100 microg/ml at 4h (25 microg/ml at 12h) is proposed. This line equates to a 1.1% risk of hepatotoxicity in abstinent alcoholic patients. The analysis supports the observation that based on the published model abstinent alcoholics might have a greater risk of hepatotoxicity after an acute acetaminophen overdose. This proposed new risk line can be used in hypothesis generation for future clinical studies in this alcohol related problem.

A Risk Quantification Instrument for Acute Acetaminophen Overdose Patients Treated With N-Acetylcysteine

STUDY OBJECTIVE

The risk of hepatotoxicity after acute acetaminophen overdose varies with timed serum acetaminophen concentration and delay to treatment. The ability to accurately predict hepatotoxicity is needed to reduce confusion about the optimal treatment regimen for individual patients and the effects of risk modifiers such as ethanol. We quantitatively estimate the risk of hepatotoxicity based on the degree and duration of pretreatment exposure to supratherapeutic concentrations of acetaminophen.

METHODS

We examined all hospitalizations for acute acetaminophen overdose within a retrospective multicenter Canadian registry. We used a previously developed composite measure incorporating timed serum acetaminophen concentration and time to N-acetylcysteine treatment into a single parameter. We then modeled hepatotoxicity on this parameter, as well as age, sex, and ethanol use. Hepatotoxicity was defined as peak aminotransferase level of 1,000 IU/L or greater at 24 hours or longer.

RESULTS

Of 1,270 admitted patients treated mostly with intravenous N-acetylcysteine for less than 24 hours, our model accurately identified the 94 patients who developed hepatotoxicity (discriminatory index 0.93). Hepatotoxicity occurred in none of the 313 patients (95% confidence interval [CI] 0% to 1.0%) above the traditional 150 mug/mL treatment line who were classified as low risk (<1%) using our instrument. After adjustment for severity of exposure, the risk of hepatotoxicity was considerably higher in the absence of coingested ethanol (median hepatotoxic dose 16.5 mmol/L x hour [95% CI 8.74 to 31.0 mmol/L x hour] versus 27.1 mmol/L x hour [95% CI 11.1 to 66.3 mmol/L x hour]), particularly among alcoholics (4.79 mmol/L x hour [95% CI 2.13 to 10.8 mmol/L x hour]).

CONCLUSION

Our risk prediction instrument identifies a large group of low-risk patients for whom 20-hour intravenous N-acetylcysteine therapy is sufficient. Our results suggest that acute and chronic ethanol use dramatically influences acetaminophen toxicity. This work may facilitate the evaluation of individualized treatment strategies for higher-risk patients.