The effect of chronic alcohol intake on prognosis and outcome in 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.

The role of alcohol consumption on acetaminophen induced liver injury: Implications from a mathematical model

Acetaminophen (APAP) overdose is one of the predominant causes of drug induced acute liver injury in the U.S and U.K. Clinical studies show that ingestion of alcohol may increase the risk of APAP induced liver injury. Chronic alcoholism may potentiate APAP hepatotoxicity and this increased risk of APAP toxicity is observed when APAP is ingested even shortly after alcohol is cleared from the body. However, clinical reports also suggest that acute alcohol consumption may have a protective effect against hepatotoxicity by inhibiting microsomal acetaminophen oxidation and thereby reducing N-acetyl-p-benzoquinone imine (NAPQI) production. The aim of this study is to model this dual role of alcohol to determine how the timing of alcohol ingestion affects APAP metabolism and resulting liver injury and identify mechanisms of APAP induced liver injury. The mathematical model is developed to capture condition of a patient of single time APAP overdose who may be an acute or chronic alcohol user. The analysis suggests that the risk of APAP-induced hepatotoxicity is increased if APAP is ingested shortly after alcohol is cleared from the body in chronic alcohol users. A protective effect of acute consumption of alcohol is also observed in patients with APAP overdose. For example, simultaneous ingestion of alcohol and APAP overdose or alcohol intake after or before few hours of APAP overdose may result in less APAP-induced hepatotoxicity when compared to a single time APAP overdose. The rate of hepatocyte damage in APAP overdose patients depends on trade-off between induction and inhibition of CYP enzyme.

Cysteine/Glutathione Deficiency: A Significant and Treatable Corollary of Disease

Glutathione (GSH) deficiency may play a pivotal role in a variety of apparently unrelated clinical conditions and diseases. Orally administered N-acetylcysteine (NAC), which replenishes the cysteine required for GSH synthesis, has been tested in a large number of randomized placebo-controlled trials involving these diseases and conditions. This chapter focused on developing a base of evidence suggesting that NAC administration improves disease by increasing cysteine and/or GSH in a variety of diseases, thereby implying a significant role for GSH deficiency in the clinical basis of many diseases. To develop this base of evidence, we systematically selected studies which considered the hypothesis that the therapeutic efficacy for NAC is an indication that cysteine and/or GSH deficiency is a pathophysiological part of the diseases studied. In this manner we focus this chapter on explaining the biological mechanisms of NAC therapy in a wide variety of disorders and demonstrate its ubiquitous role in improving disease that involves disrupted GSH and/or cysteine metabolism.

Drug Hepatotoxicity: Environmental Factors

Drug-induced liver injury presents as various forms of acute and chronic liver disease. There is wide geographic variation in the most commonly implicated agents. Smoking can induce cytochrome P450 enzymes but this does not necessarily translate into clinically relevant drug-induced liver injury. Excessive alcohol consumption is a clear risk factor for intrinsic hepatotoxicity from acetaminophen and may predispose to injury from antituberculosis medications. Understanding of the role of infection, proinflammatory states, disorders of coagulation, and the hepatic clock in predisposing patients to drug-induced liver injury is evolving. More study focusing specifically on environmental risk factors predisposing patients to drug-induced liver injury is needed.

Risk factors and outcomes of acute kidney injury in patients with acute liver failure

BACKGROUND & AIMS

Patients with acute liver failure (ALF) frequently develop renal dysfunction, yet its overall incidence and outcomes have not been fully assessed. We investigated the incidence of acute kidney injury (AKI) among patients with ALF, using defined criteria to identify risk factors and to evaluate its effect on overall outcomes.

METHODS

We performed a retrospective review of data from 1604 patients enrolled in the Acute Liver Failure Study Group, from 1998 through 2010. Patients were classified by the Acute Kidney Injury Network criteria, as well as for etiology of liver failure (acetaminophen-based, ischemic, and all others).

RESULTS

Seventy percent of patients with ALF developed AKI, and 30% received renal replacement therapy (RRT). Patients with severe AKI had higher international normalized ratio values than those without renal dysfunction (P < .001), and a higher proportion had advanced-grade coma (coma grades 3 or 4; P < .001) or presented with hypotension requiring vasopressor therapy (P < .001). A greater proportion of patients with acetaminophen-induced ALF had severe kidney injury than of patients with other etiologies of ALF; 34% required RRT, compared with 25% of patients with ALF not associated with acetaminophen or ischemia (P < .002). Of the patients with ALF who were alive at 3 weeks after study entry, significantly fewer with AKI survived for 1 year. Although AKI reduced the overall survival time, more than 50% of patients with acetaminophen-associated or ischemic ALF survived without liver transplantation (even with RRT), compared with 19% of patients with ALF attribute to other causes (P < .001). Only 4% of patients requiring RRT became dependent on dialysis.

CONCLUSIONS

Based on a retrospective analysis of data from more than 1600 patients, AKI is common in patients with ALF and affects short- and long-term outcomes, but rarely results in chronic kidney disease. Acetaminophen-induced kidney injury is frequent, but patients have better outcomes than those with other forms of ALF.

Assessing the impact of vomiting episodes on outcome after acetaminophen poisoning

Identifying indices of poor prognosis at first presentation after acetaminophen poisoning is the key to both improving clinical care and determining targets for intervention. This study intended to document the prevalence, clinical characteristics and predictors of vomiting and to investigate the relationship between episodes of vomiting at first hospital presentation and outcome in acetaminophen poisoning. This retrospective cohort study included patients who attended the emergency department and were admitted within 24 hr of acetaminophen ingestion. The study was conducted over a period of 5 years from 1 January 2004 to 31 December 2008. Parametric and non-parametric tests were used to test differences between groups depending on the normality of the data. SPSS 15 was used for data analysis. Data from 291 patients were included. Vomiting was present in 65.3% of patients with acetaminophen poisoning at the time of first presentation. Multiple logistic regression showed that significant risk factors for vomiting were present among patients who reported an ingested dose of acetaminophen ≥10 g (p < 0.001) and a latency time of more than 8 hr (p = 0.030). Overall, an increasing trend in prothrombin time (p = 0.03), serum bilirubin (p < 0.001), serum creatinine (p = 0.005), serum potassium (p < 0.001), length of hospital stay (p < 0.001) and the prevalence of patients who had a serum acetaminophen level above a 'possible toxicity' treatment line (p = 0.001) were associated with an increased number of episodes of vomiting. In conclusion, vomiting was common among patients with acetaminophen poisoning. This study suggests that an increase in episodes of vomiting at first presentation appears to be an important risk marker of subsequent nephrotoxicity and hepatotoxicity.

Association between gastrointestinal manifestations following acetaminophen poisoning and outcome in 291 acetaminophen poisoning patients

BACKGROUND

Acetaminophen poisoning is a common clinical problem, and early identification of patients with more severe poisoning is key to improving outcomes.

PURPOSES

This study intends to document prevalence, clinical characteristics, and predictors of gastrointestinal (GI) manifestations and to assess the impact of these manifestations on outcome in patients with acetaminophen poisoning.

METHODS

This is a retrospective cohort study of hospital admissions for acute acetaminophen poisoning conducted over a period of 5 years from 1 January 2004 to 31 December 2008. Parametric and non-parametric tests were used to test differences between groups depending on the normality of the data. Statistical Package for Social Sciences (SPSS) 15 was used for data analysis.

RESULTS

Two hundred and ninety-one patients were studied; their mean age was 23.01 +/- 7.4 years and 76.6% had GI manifestations. Multiple logistic regression showed that significant risk factors for GI manifestations were present among patients who reported acetaminophen dose ingested >or=10 g (p < 0.001), and latency time more than 8 hours (p = 0.030). GI manifestations at first admission predicted poorer outcomes in terms of estimated acetaminophen levels to be a possible toxic (p < 0.001), elevated bilirubin levels (p = 0.002), prolonged prothrombin time (PT; p = 0.002), elevated creatinine level (p = 0.028), declination of potassium level (p < 0.001), and prolonged hospital stay (p < 0.001).

CONCLUSIONS

GI manifestations were common among patients with acetaminophen poisoning. This study suggests that the presence of GI manifestations at first presentation appears to be an important risk marker of subsequent hepatotoxicity and nephrotoxicity.

Delayed onset of acute renal failure after significant paracetamol overdose: A case series

Acute renal failure is a recognized manifestation of paracetamol toxicity, but comparatively little data is available concerning its onset and duration. The present study sought to characterize the time course of rising serum creatinine concentrations in paracetamol nephrotoxicity. Renal failure was defined by serum creatinine concentration ≥150 μmol/L (1.69 mg/dL) or ≥50% increase from baseline. Serum creatinine concentrations and alanine aminotransferase activity were considered with respect to the interval after paracetamol ingestion. There were 2068 patients with paracetamol overdose between March 2005 and October 2007, and paracetamol nephrotoxicity occurred in 8 (0.4%). All had significant hepatotoxicity, and peak serum alanine aminotransferase activity occurred at 2.5 days (2.2 to 2.9 days) after ingestion. Peak serum creatinine concentrations did not occur until 5.5 days (4.4 to 5.9 days) after ingestion (p = .031 by Wilcoxon test). Serum creatinine concentrations slowly restored to normal, and renal replacement was not required. In this patient series, rising serum creatinine concentrations only became detectable after more than 48 hours after paracetamol ingestion. Therefore, renal failure might easily be missed if patients are discharged home before this. Further work is required to establish the prevalence of paracetamol-induced nephrotoxicity, and its clinical significance.

Proteinuria is unrelated to the extent of acute acetaminophen overdose: a prospective clinical study

BACKGROUND

Acute renal failure is a recognized complication of acute acetaminophen overdose. Its detection depends on rising creatinine concentrations, which is an insensitive method. The present study examined whether proteinuria might correspond with the extent of acute acetaminophen exposure as a possible early marker of renal effects.

METHODS

A prospective case-control study included patients attending the emergency department within 24 hours of acetaminophen ingestion. A urine specimen was collected within 12 hours of hospital attendance for creatinine, albumin, and protein determination. Equivalent 4-hour acetaminophen concentrations were used to indicate drug exposure: mild if >100 g/L (>662 mmol/L), moderate if 100-200 g/L (662-1323 mmol/L), or severe if <200 g/L (<1323 mmol/L). Data are presented as median (interquartile range) and groups compared using Mann Whitney and chi-square tests.

RESULTS

Seventy patients were studied (17 men, 53 women), age 37 years (23-45 years). The stated acetaminophen dose was 15 g (8-20 g), and interval between ingestion and presentation was 4.6 hours (4.1-7.9 hours). Urinary albumin concentrations were 8 mg/L (0-12 mg/L) in the mild group, 12 mg/L (5-25 mg/L) in the moderate group, and 11 mg/L (6-22 mg/L) in the severe group. Total protein concentrations were 90 mg/L (50-183 mg/L), 70 mg/L (40 to 130 mg/L), and 110 mg/L (75-205 mg/L), respectively. The proportions of patients who had urine albumin:creatinine ratio >3 mg/mmol were 20.8%, 23.5%, and 21.2%, respectively. None of the patients developed acute renal failure.

CONCLUSIONS

No relationship was found between the extent of acute acetaminophen exposure and proteinuria. Further work is required to examine whether urinary protein excretion is altered in patients who subsequently develop acute renal failure following acetaminophen overdose.

Acute ethanol coingestion confers a lower risk of hepatotoxicity after deliberate acetaminophen overdose

OBJECTIVES

Little is known about the clinical significance of acute ethanol coingestion around the time of acetaminophen (paracetamol) overdose. This study prospectively examined the effect of acute ethanol coingestion on risk of hepatotoxicity among patients admitted to hospital for N-acetylcysteine (NAC) therapy after deliberate acetaminophen overdose.

METHODS

This was a prospective observational study and included sequential patients who presented within 24 hours of acute acetaminophen ingestion and required NAC therapy. Significant hepatotoxicity was defined by alanine transaminase > 1,000 U/L or the international normalized ratio > 1.3 after a standardized intravenous administration of 300 mg/kg NAC.

RESULTS

There were 362 patients, including 178 (49.2%) who coingested ethanol acutely. The prevalence of hepatotoxicity was 5.1% (95% CI = 2.6% to 9.5%) in those who ingested ethanol, compared to 15.2% (95% CI = 10.7% to 21.2%) in those who did not (p = 0.0027 by chi-square proportional test). Acute ethanol intake conferred a lower risk of hepatotoxicity in patients who had acetaminophen concentrations above or below the "200-line" and was independent of the interval between ingestion and assessment.

CONCLUSIONS

Acute ethanol intake is associated with a lower risk of hepatotoxicity after acetaminophen overdose. This apparent protective effect cannot be explained solely by lower exposure to acetaminophen in this group, nor differences in the interval between ingestion and initiation of treatment. Further work is required to establish mechanisms by which ethanol might confer protection against hepatotoxicity, so as to identify novel strategies for reducing risk after acute acetaminophen ingestion.

The effect of acetaminophen (four grams a day for three consecutive days) on hepatic tests in alcoholic patients--a multicenter randomized study

BACKGROUND

Hepatic failure has been associated with reported therapeutic use of acetaminophen by alcoholic patients. The highest risk period for alcoholic patients is immediately after discontinuation of alcohol intake. This period exhibits the largest increase in CYP2E1 induction and lowest glutathione levels. Our hypothesis was that common liver tests would be unaffected by administration of the maximum recommended daily dosage of acetaminophen for 3 consecutive days to newly-abstinent alcoholic subjects.

METHODS

Adult alcoholic subjects entering two alcohol detoxification centers were enrolled in a prospective double-blind, randomized, placebo-controlled trial. Subjects were randomized to acetaminophen, 4 g/day, or placebo for 3 consecutive days. The study had 95% probability of detecting a 15 IU/L difference in serum ALT.

RESULTS

A total of 443 subjects were enrolled: 308 (258 completed) received acetaminophen and 135 subjects (114 completed) received placebo. Study groups did not differ in demographics, alcohol consumption, nutritional status or baseline laboratory assessments. The peak mean ALT activity was 57 +/- 45 IU/L and 55 +/- 48 IU/L in the acetaminophen and placebo groups, respectively. Subgroup analyses for subjects presenting with an elevated ALT, subjects fulfilling a diagnosis of alcoholic hepatitis and subjects attaining a peak ALT greater than 200 IU/L showed no statistical difference between the acetaminophen and control groups. The one participant developing an increased international normalized ratio was in the placebo group.

CONCLUSION

Alcoholic patients treated with the maximum recommended daily dose of acetaminophen for 3 consecutive days did not develop increases in serum transaminase or other measures of liver injury. Treatment of pain or fever for 3 days with acetaminophen appears safe in newly-abstinent alcoholic patients, such as those presenting for acute medical care.

Repeated supratherapeutic doses of paracetamol in children--a literature review and suggested clinical approach

The safety of paracetamol when given in the recommended dosage is well documented. However, in recent years there have been many reports of liver failure associated with repeated exposure to supratherapeutic doses of paracetamol. This paper reviews the literature on chronic supratherapeutic paracetamol exposure in children and the different dosing guidelines. Based on which, we suggest the following approach: liver injury secondary to repeated dosing of paracetamol should be considered when a child has received more than 75 mg/kg/d for at least 2 d, or if risk factors for paracetamol toxicity have been identified. Liver transaminases, coagulation factors, and paracetamol serum concentrations should be measured in these children and in symptomatic children with vomiting, right upper quadrant abdominal pain, and jaundice who have taken paracetamol. Treatment with N-acetyl cysteine should be started regardless of paracetamol concentrations if transaminases or INR are elevated.

CONCLUSION

Liver injury secondary to repeated dosing of paracetamol is rare but may result in severe morbidity and mortality. The cumulative dose of paracetamol should not exceed 75 mg/kg/d. Children treated with higher doses for more than 2 d should be evaluated for possible liver injury and treated with N-acetyl cysteine if evidence of liver injury is found.

Interventions for paracetamol (acetaminophen) overdose

BACKGROUND

Poisoning with paracetamol (acetaminophen) is a common cause of hepatotoxicity in the Western World. Inhibition of absorption, removal from the vascular system, antidotes, and liver transplantation are interventions for paracetamol poisoning.

OBJECTIVES

To assess the benefits and harms of interventions for paracetamol overdose.

SEARCH STRATEGY

We identified trials through electronic databases, manual searches of bibliographies and journals, authors of trials, and pharmaceutical companies until December 2005.

SELECTION CRITERIA

Randomised clinical trials and observational studies were included.

DATA COLLECTION AND ANALYSIS

The primary outcome measure was all-cause mortality plus liver transplantation. Secondary outcome measures were clinical symptoms, (eg, hepatic encephalopathy, fulminant hepatic failure), hepatotoxicity, adverse events, and plasma paracetamol concentration. We used Peto odds ratios and odds ratios with 95% confidence intervals (CI) for analysis of outcomes. Random- and fixed-effects meta-analyses were performed.

MAIN RESULTS

Ten small and low-methodological quality randomised trials, one quasi-randomised study, and 48 observational studies were identified. It was not possible to perform relevant meta-analyses of randomised trials that have addressed our outcome measures. Activated charcoal, gastric lavage, and ipecacuanha are able to reduce the absorption of paracetamol, but the clinical benefit is unclear. Of these, activated charcoal seems to have the best risk-benefit ratio. N-acetylcysteine seems preferable to placebo/supportive treatment, dimercaprol, and cysteamine, but N-acetylcysteine's superiority to methionine is unproven. It is not clear which N-acetylcysteine treatment protocol offers the best efficacy. No strong evidence supports other interventions for paracetamol overdose. N-acetylcysteine may reduce mortality in patients with fulminant hepatic failure (Peto OR 0.26, 95% CI 0.09 to 0.94, one trial). Liver transplantation has the potential to be life saving in fulminant hepatic failure, but refinement of selection criteria for transplantation and long-term outcome reporting are required.

AUTHORS' CONCLUSIONS

Our results highlight a paucity of randomised trials on interventions for paracetamol overdose. Activated charcoal seems the best choice to reduce absorption. N-acetylcysteine should be given to patients with overdose but the selection criteria are not clear. No N-acetylcysteine regime has been shown to be more effective than any other. It is a delicate balance when to proceed to liver transplantation, which may be life-saving for patients with poor prognosis.

Acetaminophen poisoning: an evidence-based consensus guideline for out-of-hospital management

The objective of this guideline is to assist poison center personnel in the appropriate out-of-hospital triage and initial management of patients with suspected ingestions of acetaminophen. An evidence-based expert consensus process was used to create this guideline. This guideline applies to ingestion of acetaminophen alone and is based on an assessment of current scientific and clinical information. The expert consensus panel recognizes that specific patient care decisions may be at variance with this guideline and are the prerogative of the patient and the health professionals providing care. The panel's recommendations follow. These recommendations are provided in chronological order of likely clinical use. The grade of recommendation is provided in parentheses. 1) The initial history obtained by the specialist in poison information should include the patient's age and intent (Grade B), the specific formulation and dose of acetaminophen, the ingestion pattern (single or multiple), duration of ingestion (Grade B), and concomitant medications that might have been ingested (Grade D). 2) Any patient with stated or suspected self-harm or who is the recipient of a potentially malicious administration of acetaminophen should be referred to an emergency department immediately regardless of the amount ingested. This referral should be guided by local poison center procedures (Grade D). 3) Activated charcoal can be considered if local poison center policies support its prehospital use, a toxic dose of acetaminophen has been taken, and fewer than 2 hours have elapsed since the ingestion (Grade A). Gastrointestinal decontamination could be particularly important if acetylcysteine cannot be administered within 8 hours of ingestion. Acute, single, unintentional ingestion of acetaminophen: 1) Any patient with signs consistent with acetaminophen poisoning (e.g., repeated vomiting, abdominal tenderness in the right upper quadrant or mental status changes) should be referred to an emergency department for evaluation (Grade D). 2) Patients less than 6 years of age should be referred to an emergency department if the estimated acute ingestion amount is unknown or is 200 mg/kg or more. Patients can be observed at home if the dose ingested is less than 200 mg/kg (Grade B). 3) Patients 6 years of age or older should be referred to an emergency department if they have ingested at least 10 g or 200 mg/kg (whichever is lower) or when the amount ingested is unknown (Grade D). 4) Patients referred to an emergency department should arrive in time to have a stat serum acetaminophen concentration determined at 4 hours after ingestion or as soon as possible thereafter. If the time of ingestion is unknown, the patient should be referred to an emergency department immediately (Grade D). 5) If the initial contact with the poison center occurs more than 36 hours after the ingestion and the patient is well, the patient does not require further evaluation for acetaminophen toxicity (Grade D). Repeated supratherapeutic ingestion of acetaminophen (RSTI): 1) Patients under 6 years of age should be referred to an emergency department immediately if they have ingested: a) 200 mg/kg or more over a single 24-hour period, or b) 150 mg/kg or more per 24-hour period for the preceding 48 hours, or c) 100 mg/kg or more per 24-hour period for the preceding 72 hours or longer (Grade C). 2) Patients 6 years of age or older should be referred to an emergency department if they have ingested: a) at least 10 g or 200 mg/kg (whichever is less) over a single 24-hour period, or b) at least 6 g or 150 mg/kg (whichever is less) per 24-hour period for the preceding 48 hours or longer. In patients with conditions purported to increase susceptibility to acetaminophen toxicity (alcoholism, isoniazid use, prolonged fasting), the dose of acetaminophen considered as RSTI should be greater than 4 g or 100 mg/kg (whichever is less) per day (Grade D). 3) Gastrointestinal decontamination is not needed (Grade D). Other recommendations: 1) The out-of-hospital management of extended-release acetaminophen or multi-drug combination products containing acetaminophen is the same as an ingestion of acetaminophen alone (Grade D). However, the effects of other drugs might require referral to an emergency department in accordance with the poison center's normal triage criteria. 2) The use of cimetidine as an antidote is not recommended (Grade A).

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.

Acute poisoning: understanding 90% of cases in a nutshell

The acutely poisoned patient remains a common problem facing doctors working in acute medicine in the United Kingdom and worldwide. This review examines the initial management of the acutely poisoned patient. Aspects of general management are reviewed including immediate interventions, investigations, gastrointestinal decontamination techniques, use of antidotes, methods to increase poison elimination, and psychological assessment. More common and serious poisonings caused by paracetamol, salicylates, opioids, tricyclic antidepressants, selective serotonin reuptake inhibitors, benzodiazepines, non-steroidal anti-inflammatory drugs, and cocaine are discussed in detail. Specific aspects of common paediatric poisonings are reviewed.

Should a lower treatment line be used when treating paracetamol poisoning in patients with chronic alcoholism?: a case for

A lower threshold for treatment of paracetamol (acetaminophen) poisoning has been advocated in chronic heavy users of alcohol, based originally on animal studies indicating that chronic alcohol ingestion increased hepatotoxicity. This was attributed to increased production of the toxic metabolite, N-acetyl-p-benzoquinoneimine, by cytochrome P450 (CYP)2E1 induction. The clinical evidence for increased risk is limited to four retrospective studies with potential for referral and reporting bias and conflicting results. No study has specifically addressed the issue of the treatment threshold for acute paracetamol overdose in chronic alcohol users. However, animal studies in multiple species have consistently shown a lower dose of paracetamol is required to produce hepatotoxicity after chronic alcohol use. The knowledge of potential mechanisms has expanded to include effects of other alcohols, such as isopentanol, induction of CYP enzymes other than CYP2E1 and glutathione depletion. There are no convincing reasons or data to suggest these findings do not apply to humans. However, further human toxicokinetic and clinical research is required to quantify the extent of the interaction. Arguments about treating overdoses should not be confused with those about whether there is an alcohol-paracetamol interaction at therapeutic doses. Halving the threshold dose/concentration for treatment is a conservative educated guess that has been widely adopted. In overdose, the potential benefits of treatment at this lower threshold clearly outweigh the minimal risks of acetylcysteine.

Paracetamol overdose: an evidence based flowchart to guide management

A flowchart for the management of patients with paracetamol poisoning is presented to help clinicians in the emergency department.

Acute versus chronic alcohol consumption in acetaminophen-induced hepatotoxicity

The aim of this study was to determine by multivariate analysis how alcohol and other factors affect the clinical course and outcome in patients with acetaminophen (paracetamol) poisoning. A total of 645 consecutive patients admitted from 1994 to 2000 with single-dose acetaminophen poisoning were studied, giving special attention to alcohol history, time between overdose and intravenous N-acetylcysteine (NAC) treatment ("time to NAC"), and other data available at the time of admittance. Up until 72 hours after ingestion, time to NAC was the single most important independent risk factor. With a time to NAC less than 12 hours, the mortality rate was 0.42% (95% CI, 0.05-2.7). When time to NAC exceeded 12, 24, and 48 hours, the mortality rate increased to 6.1%, 13%, and 19%, respectively. Chronic alcohol abuse was an independent risk factor of mortality (odds ratio [OR], 3.52; 95% CI, 1.78-6.97). Acute alcohol ingestion was an independent protective factor regarding mortality in alcoholic patients (OR, 0.08; 95% CI, 0.01-0.66) but not in nonalcoholic patients (OR, 0.21; 95% CI, 0.03-1.67). Patient age and quantity of acetaminophen were independent risk factors. In conclusion, time to NAC was confirmed as the major risk factor in acetaminophen-induced hepatotoxicity and mortality. Chronic alcohol abuse was an independent risk factor that could be counteracted by concomitant acute alcohol ingestion. We suggest that patients with chronic alcoholism and suspected acetaminophen poisoning due to an increased risk of developing hepatotoxicity should be treated with NAC regardless of risk estimation.

Alcohol exposure and paracetamol-induced hepatotoxicity

Most instances of hepatotoxicity due to paracetamol in the United Kingdom and Australia are the result of large overdoses of the drug taken with suicidal or parasuicidal intent. In contrast, serious hepatotoxicity at recommended or near-recommended doses for therapeutic purposes has been reported, mainly from the United States and in association with chronic alcohol use, leading to the widely held belief that chronic alcoholics are predisposed to paracetamol-related toxicity at relatively low doses. Yet the effects of alcohol on paracetamol metabolism are complex. Studies performed in both experimental animals and humans indicate that chronic alcohol use leads to a short-term, two- to threefold increase in hepatic content of cytochrome P4502E1, the major isoform responsible for the generation of the toxic metabolite from paracetamol, although increased oxidative metabolism of paracetamol at recommended doses has not been demonstrated clinically. A reduced hepatic content of glutathione, required to detoxify the reactive metabolite, has been documented in chronic alcoholics, due probably to associated fasting and malnutrition, providing a metabolic basis for any possible predisposition of this group to hepatotoxicity at relatively low paracetamol doses. Simultaneous alcohol and paracetamol ingestion reduces oxidative metabolism of paracetamol in both rodents and humans, predominantly as a consequence of depletion in cytosol of free NADPH. The possibilities that chronic alcohol use may predispose to paracetamol-related hepatotoxicity and that alcohol taken with paracetamol may protect against it, based on these metabolic observations, are examined in this review.

Influence of acute and chronic alcohol intake on the clinical course and outcome in acetaminophen overdose

BACKGROUND

Animal studies on acetaminophen toxicity suggest that chronic alcohol intake affects the outcome adversely, whereas acute alcohol intake seems protective. Few clinical data are available.

METHODS

We studied 209 consecutive patients with single-dose acetaminophen overdose. The combined influence of independent variables (gender, age, dose, delay to antidote treatment, chronic and acute alcohol intake and nomogram risk group) on dependent variables (death, development of hepatic encephalopathy and biochemical liver markers) was studied using multiple or logistic regression analysis.

RESULTS

Fifty-seven (27.3%) patients had chronic alcohol intake and 45 (21.5%) patients had acute alcohol intake. Forty-four (21.1%) patients developed hepatic coma and 20 (43.5%) of these patients died. Chronic alcohol intake was significantly and independently associated with the development of hepatic coma, with a lower prothrombin index, lower platelet count, higher creatinine and higher bilirubin. The relative risks for hepatic coma and death were 5.3 (95% confidence interval, 2.2-12.4) and 1.4 (95% confidence interval, 0.5-3.9), respectively, in the chronic alcohol intake group compared with the no chronic alcohol intake group. Acute alcohol intake was not significantly associated with any of the dependent variables studied.

CONCLUSIONS

Chronic alcohol intake enhances acetaminophen hepatotoxicity, whereas acute alcohol intake does not affect the clinical course.

Management of paracetamol overdose: current controversies

Paracetamol (acetaminophen) is one of the most frequently used analgesics, and is the most commonly used substance in self-poisoning in the US and UK. Paracetamol toxicity is manifested primarily in the liver. Treatment with N-acetyl-cysteine (NAC), if started within 10 hours from ingestion, can prevent hepatic damage in most cases. Pharmacokinetic data relating plasma paracetamol concentration to time after ingestion have been used to generate a 'probable hepatoxicity line' to predict which cases of paracetamol overdose will result in hepatotoxicity and should be treated with NAC. However, later studies use a 25% lower line as their 'possible hepatotoxicity line'. Although adopting the original line may save considerable resources, further studies are needed to determine whether such an approach is safe. On the basis of the metabolism of paracetamol, several risk factors for paracetamol toxicity have been proposed. These risk factors include long term alcohol (ethanol) ingestion, fasting and treatment with drugs that induce the cytochrome P450 2E1 enzyme system. Although some studies have suggested that these risk factors may be associated with worse prognosis, the data are inconclusive. However, until further evidence is available, we suggest that the lower line should be used when risk factors are present. In Canada and the UK, the intravenous regimen for NAC is used almost exclusively; in the US, an oral regimen is used. Both regimens have been shown to be effective. There is no large scale study with direct comparison between these 2 therapeutic protocols and controversy still exists as to which regimen is superior. During the last few years there has been an increase in the number of reports of liver failure associated with prolonged paracetamol administration for therapeutic reasons. The true incidence of this phenomenon is not known. We suggest testing liver enzyme levels if a child has received more than 75 mg/kg/day of paracetamol for more than 24 hours during febrile illness, and to treat with NAC when transaminase levels are elevated. Paracetamol overdose during pregnancy should be treated with either oral or intravenous NAC according to the regular protocols in order to prevent maternal, and potentially fetal, toxicity. Unless severe maternal toxicity develops, paracetamol overdose does not appear to increase the risk for adverse pregnancy outcome.

Interventions for paracetamol (acetaminophen) overdoses

BACKGROUND

Self-poisoning with paracetamol (acetaminophen) is a common cause of hepatotoxicity in the Western World. Interventions for paracetamol poisoning encompass inhibition of absorption, removal from the vascular system, antidotes, and liver transplantation.

OBJECTIVES

The objective was to assess the beneficial and harmful effects of interventions or combination of interventions for paracetamol overdose.

SEARCH STRATEGY

The Cochrane Hepato-Biliary Group Controlled Trials Register, The Cochrane Library, MEDLINE, EMBASE, and text searches were combined (until July 2001).

SELECTION CRITERIA

Randomised clinical trials (RCTs) and observational studies as well as human volunteer randomised trials were included. The studies could be unpublished or published as an article, an abstract, or a letter and no language limitations were applied.

DATA COLLECTION AND ANALYSIS

All the analyses were performed according to the intention to treat. The methodological quality of the included trials was evaluated by components of methodological quality.

MAIN RESULTS

Nine RCTs (all small and of low methodological quality), one quasi-randomised trials, 37 observational studies, and nine randomised trials including human volunteers were identified. It was impossible to perform meta-analyses including more than two RCTs. Activated charcoal, gastric lavage, and ipecacuanha are able to reduce the absorption of paracetamol but the clinical benefit is unclear. Of these, activated charcoal seems to have the best risk-benefit ratio. N-acetylcysteine seems preferable to placebo/supportive treatment (relative risk of mortality in patients with fulminant hepatic failure = 0.65; 95% confidence interval 0.43 to 0.99), dimercaprol, and cysteamine, but N-acetylcysteine's superiority to methionine is unproven. It is not clear which N-acetylcysteine treatment protocol offers the best efficacy. No evidence supports haemoperfusion or cimetidine for paracetamol overdose. Liver transplantation has the potential to be life saving in fulminant hepatic failure, but further refinement of selection criteria for liver transplantation and evaluation of the long-term outcome are required.

REVIEWER'S CONCLUSIONS

This systematic Review has highlighted a paucity of RCTs on interventions for paracetamol overdose. Activated charcoal seems the best choice to reduce paracetamol absorption. N-acetylcysteine should be given to patients with paracetamol overdose. No N-acetylcysteine regime has been shown to be more effective than any other. It is a delicate balance when to proceed to liver transplantation, which may be life saving in patients with a poor prognosis. Interventions for paracetamol overdose need assessment in high-quality, multi-centre RCTs.

Paracetamol, alcohol and the liver

It is claimed that chronic alcoholics are at increased risk of paracetamol (acetaminophen) hepatotoxicity not only following overdosage but also with its therapeutic use. Increased susceptibility is supposed to be due to induction of liver microsomal enzymes by ethanol with increased formation of the toxic metabolite of paracetamol. However, the clinical evidence in support of these claims is anecdotal and the same liver damage after overdosage occurs in patients who are not chronic alcoholics. Many alcoholic patients reported to have liver damage after taking paracetamol with 'therapeutic intent' had clearly taken substantial overdoses. No proper clinical studies have been carried out to investigate the alleged paracetamol-alcohol interaction and acute liver damage has never been produced by therapeutic doses of paracetamol given as a challenge to a chronic alcoholic. The paracetamol-alcohol interaction is complex; acute and chronic ethanol have opposite effects. In animals, chronic ethanol causes induction of hepatic microsomal enzymes and increases paracetamol hepatotoxicity as expected (ethanol primarily induces CYP2E1 and this isoform is important in the oxidative metabolism of paracetamol). However, in man, chronic alcohol ingestion causes only modest (about twofold) and short-lived induction of CYP2E1, and there is no corresponding increase (as claimed) in the toxic metabolic activation of paracetamol. The paracetamol-ethanol interaction is not specific for any one isoform of cytochrome P450, and it seems that isoenzymes other than CYP2E1 are primarily responsible for the oxidative metabolism of paracetamol in man. Acute ethanol inhibits the microsomal oxidation of paracetamol both in animals and man. This protects against liver damage in animals and there is evidence that it also does so in man. The protective effect disappears when ethanol is eliminated and the relative timing of ethanol and paracetamol intake is critical. In many of the reports where it is alleged that paracetamol hepatotoxicity was enhanced in chronic alcoholics, the reverse should have been the case because alcohol was actually taken at the same time as the paracetamol. Chronic alcoholics are likely to be most vulnerable to the toxic effects of paracetamol during the first few days of withdrawal but maximum therapeutic doses given at this time have no adverse effect on liver function tests. Although the possibility remains that chronic consumption of alcohol does increase the risk of paracetamol hepatotoxicity in man (perhaps by impairing glutathione synthesis), there is insufficient evidence to support the alleged major toxic interaction. It is astonishing that clinicians and others have unquestion-ingly accepted this supposed interaction in man for so long with such scant regard for scientific objectivity.

Fulminant hepatic failure

In recent years, considerable progress has been made in developing specific and supportive medical measures that have improved prognosis in FHF. Although new techniques for cell culture and perfusion have also resulted in a number of promising devices for the provision of temporary liver support, their clinical efficacy is as yet uncertain. Controlled multicenter trials in well-defined patient groups and with standardized outcome measures will be essential to evaluate the clinical value of these devices properly. The same considerations must also apply in assessing the efficacy of hepatocyte transplantation in FHF. A better understanding of mechanisms responsible for liver cell death and multiorgan failure, and the development of strategies to enhance liver regeneration may, in the future, allow a more targeted approach to therapy.

Protective effect of ethanol against acetaminophen-induced hepatotoxicity in mice: role of NADH:quinone reductase

The role of NAD(P)H:quinone reductase (QR; EC 1.6.99.2) in the alcohol-derived protective effect against hepatotoxicity caused by acetaminophen (APAP) was studied. In mice pretreated with dicoumarol (30 mg/kg), an inhibitor of QR, hepatic necrosis caused by APAP (400 mg/kg) was potentiated. Hepatocellular injuries induced by APAP, as assessed by liver histology, serum aminotransferase activities, hepatic glutathione (reduced and oxidized) contents, and liver microsomal aminopyrine N-demethylase activities, all were potentiated by pretreatment of mice with dicoumarol. Even in mice given APAP and ethanol (4 g/kg), in which APAP-inducible hepatic necrosis was abolished, the dicoumarol pretreatment again produced moderate hepatotoxicity and reversed the protective effect of ethanol. In mice pretreated with dicoumarol and ethanol, levels of APAP in blood and bile fluid between 90 and 240 min were higher than those in mice given ethanol. However, the biliary contents of sulfate and glucuronide conjugates of APAP were much lower than those in the ethanol group, particularly at early time points. In contrast, the biliary level of APAP-cysteine conjugate, which in the ethanol group was at its basal level, was increased maximally in the dicoumarol-pretreated mice. In the mice given dicoumarol and ethanol, the biliary APAP-cysteine conjugate level was increased moderately. These results suggest that ethanol inhibited not only the microsomal (CYP2E1 mediated) formation of a toxic quinone metabolite from APAP, but also accelerated the conversion of the toxic quinone metabolite produced back to APAP by stimulating cytoplasmic QR activity. In the presence of dicoumarol, however, QR activity was inhibited, and conversion of the toxic quinone metabolite back to APAP became inhibited and diminished the alcohol-dependent protective effect against APAP-induced hepatic injury.

Population-based incidence and outcome of acetaminophen poisoning by type of ingestion

OBJECTIVES

1) To determine, in a population-based sample, the observed frequency of acetaminophen overdose-related ED evaluation and hospitalization. 2) To examine the relative frequency of hospitalization by pattern of ingestion, the outcome of each group, and the presence or absence of postulated risk factors.

METHODS

This study was a 46-month, retrospective chart review of all acetaminophen-related visits, by patients at least 10 years of age, to either of the two hospitals that serve a four-county region of central Virginia.

RESULTS

Of 636 charts identified for review, only 137 involved acute or chronic acetaminophen overdose. One hundred twenty-six patients presented after an acute ingestion; 122 of these patients gave a history of a single, supratherapeutic ingestion of acetaminophen. Twenty-five patients were hospitalized for treatment. Eighteen of these were treated with N-acetylcysteine (NAC) based on the Rumack-Matthew nomogram; one suffered significant hepatic injury. The other seven presented at least 18 hours after ingestion, with no measurable serum acetaminophen. Two of these suffered significant hepatic injury. Four additional patients presented after multiple ingestions within 24 hours. Three were hospitalized, but none experienced significant injury. Only 11 patients were evaluated for chronic acetaminophen overmedication for pain (more than 6 g/day over a period of more than 24 hours). Four were admitted for treatment; three suffered significant hepatic injury. Thus, the observed incidence of acute acetaminophen ingestion in this region was 21.4/100,000/yr (95% CI = 17.7 to 25.2). The observed incidence of hospitalization for acute acetaminophen toxicity was 4.8/100,000/yr (95% CI = 3.0 to 6.5). The observed incidence of hospitalization for all acetaminophen poisoning was 5.5/100,000/yr (95% CI = 4.1 to 7.0). High ethanol consumption was present more frequently in those who suffered hepatic injury.

CONCLUSIONS

Most patients evaluated for acetaminophen ingestion present early following acute single overdose. Relatively few of these patients require hospitalization and, for those hospitalized, the outcome is good. More significantly, acetaminophen overdose patients whose risk cannot be estimated using the Rumack-Matthew nomogram represented 44% of those hospitalized and 83% of those who suffered significant hepatic injury. Emergency physicians need to determine how they can impact the outcome of these patients. Efforts should be directed at further characterizing historical, physical, and biochemical markers of risk and at determining in which circumstances hospitalization for NAC or other therapies is justified.

Mechanism of action and value of N-acetylcysteine in the treatment of early and late acetaminophen poisoning: a critical review

INTRODUCTION

The mechanism of action of N-acetylcysteine in early acetaminophen poisoning is well understood, but much remains to be learned of the mechanism of its possible benefit in acetaminophen poisoning presenting beyond 15 hours.

METHODS

Selective review of medical literature. N-acetylcysteine should be used in all cases of early acetaminophen poisoning where the plasma acetaminophen concentration lies "above the line;" which line is chosen depends on individual preference and whether enzyme induction is suspected. Particular care should be taken with the use of the nomogram for patients with chronic excess ingestion of acetaminophen or for those who have taken slow-release formulations.

CONCLUSIONS

While there is a trend suggesting a beneficial effect of N-acetylcysteine in some patients presenting beyond 15 hours, further research is necessary to establish just how effective N-acetylcysteine is, particularly in patients presenting with fulminant hepatic failure. Candidate mechanisms for a beneficial effect in-clude improvement of liver blood flow, glutathione replenishment, modification of cytokine production, and free radical or oxygen scavenging. Hemody-namic and oxygen delivery and utilization parameters must be monitored carefully during delayed N-acetylcysteine treatment of patients with fulminant hepatic failure, as unwanted vasodilation may be deleterious to the maintenance of mean arterial blood pressure.

Efficacy of oral versus intravenous N-acetylcysteine in acetaminophen overdose: results of an open-label, clinical trial

We compared the clinical course of pediatric patients (n = 25) with acetaminophen poisoning treated with an investigational intravenous preparation of N-acetylcysteine (IV-NAC) with that of historical control subjects (n = 29) treated with conventional oral NAC (O-NAC) therapy. Patients received IV-NAC for 52 hours; historical control subjects received O-NAC (72 hours). There were no significant intergroup differences between treatment groups in age (15.5 vs 15.9 years), gender (88% vs 90% female) or distribution of risk categories (probable risk, 12 vs 15; high risk; 13 vs 14). The peak prothrombin time was significantly higher in the IV-NAC group (14.2 vs 13.6 seconds; p = 0.048). Mean treatment delay was significantly longer in the IV-NAC group (14.4 vs 10.4 hours; p = 0.001). Hepatoxicity was noted in two (8.0%) patients in the IV-NAC treatment group and two (6.9%) patients in the O-NAC group. All patients recovered. Our results indicate that 52 hours of intravenous NAC is as effective as 72 hours of oral NAC.

The impact of nationally distributed guidelines on the management of paracetamol poisoning in accident and emergency departments. National Poison Information Service

OBJECTIVE

To assess the impact of the treatment guidelines on the management of paracetamol self poisoning in accident and emergency (A&E) departments.

METHODS

24 A&E departments in Wales and England provided details of their management of paracetamol poisoning before and after the distribution of national treatment guidelines to all A&E departments in the United Kingdom.

RESULTS

Significant increases were seen in the availability of formal written policies, the display of treatment nomograms, the recommendation to treat beyond 16 hours after ingestion, and to use a lower line on the treatment nomogram for patients at special risk of paracetamol induced liver damage.

CONCLUSIONS

Regularly updated guidelines in the management of paracetamol poisoning should be displayed in A&E departments so that medical and nursing personnel have access to the best current information on the treatment of poisoning with this frequently used drug.

Pharmacokinetics of N-acetylcysteine are altered in patients with chronic liver disease

BACKGROUND

The threshold plasma paracetamol concentration at which N-acetylcysteine (NAC) treatment is recommended to treat paracetamol poisoning in a patient with induced liver enzymes (for example, with chronic liver disease or taking anticonvulsant drugs) is 50% lower than in a patient without induced liver enzymes. More patients with chronic liver disease might therefore be expected to be exposed to NAC treatment than previously. In addition, there is increasing use of NAC in patients with chronic liver disease for multiorgan failure or hepatorenal syndrome. Little is known of NAC's pharmacokinetic properties in patients with cirrhosis.

AIM

The aim was to determine if the pharmacokinetics of NAC are altered by chronic liver disease.

SUBJECTS AND METHODS

NAC was given intravenously in a dose of 600 mg over 3 min to nine patients with biopsy-proven cirrhosis (Child's grade; 1 A, 4 B, 4 C: aetiology: 7 alcohol-related, 1 primary biliary cirrhosis, 1 secondary biliary stenosis) and six healthy matched controls. Venous blood was taken at 20, 40, 60 and 90 min then at 2, 3, 4, 6, 8 and 10 h after NAC administration. Serum NAC was estimated by HPLC. The data were normalized to a standard body weight of 70 kg.

RESULTS

The area under the serum concentration-time curve was increased (152.34 mg/L.h +/- 50.38 s.d.) in cirrhotics compared with normal controls (93.86 mg/L.h +/- 9.60 s.d.) (P < 0.05). The clearance of NAC was reduced in patients with chronic liver disease (4.52 L/h +/- 1.87 s.d.) compared with controls (6.47 L/h +/- 0.78: P < 0.01).

CONCLUSIONS

Increased vigilance for untoward anaphylactoid reactions is necessary in cirrhotics as they may have higher plasma NAC concentrations. Further studies to determine the optimum dosage regimen in such patients are required.

Protective effects of diallyl sulfide on acetaminophen-induced toxicities

Diallyl sulfide (DAS), a major flavour component of garlic, is known to modulate drug metabolism and may protect animals from chemically induced toxicity and carcinogenesis. In this study the effects of DAS on the oxidative metabolism and hepatotoxicity induced by acetaminophen (APAP) in rats were investigated. In the hepatotoxicity evaluation of Fischer 344 rats there was a dose-dependent increase in the odds of mortality rate by APAP (P = 0.009); DAS treatment significantly protected rats from APAP-related mortality (P = 0.026). Liver toxicity determined by lactate dehydrogenase activity was significantly increased by APAP treatment (0.75 g/kg). Pretreatment with DAS protected animals from APAP-induced liver toxicity in a time- and dose-dependent fashion. Treatment of DAS (50 mg/kg) 3 hr after APAP dosing significantly (P < 0.05) protected rats from APAP-induced liver toxicity. The metabolism of APAP (50 microM) in vitro was significantly inhibited by DAS (0.3-1 mM) in liver microsomes isolated from F344 rats. As the effect of DAS on APAP-induced hepatotoxicity in vivo was observed only when DAS was administered before or shortly after (< 3 hr) APAP dosing, data suggested that the protective effect of DAS is mainly at the metabolic activation step of APAP. However, the possibility that DAS may also have effects on other drug metabolism systems, such as glutathione (GSH) and glutathione S-transferases, cannot be ruled out.

Comparison of thermally oxidized lipids and acetaminophen with concurrent consumption of ethanol as inducers of liver cirrhosis

The mechanism(s) of liver damage initiated by ingestion of toxic components of thermally oxidized lipids was compared in a rat model with the documented mechanisms of hepatic failure and necrosis initiated by acetaminophen. Acetaminophen (50 mg/kg body weight) or oxidized lipids (0.15 ml oxidized trilinolein or 1.05 ml oxidized butter oil per rat) were intubated at 12-h intervals to rats. Treated rats were allowed free access to food and water containing 3% ethanol. Changes in relative concentration of acute-phase plasma proteins, determined by two-dimensional (2D) immunoelectrophoresis, were taken as a marker of liver damage. In contrast to simple inflammation, acute-phase plasma proteins in this study disproportionately increased or decreased as histological damage of the liver due to intubation oxidized lipids or acetaminophen. Histological examination of liver of rats intoxicated with oxidized lipids revealed severe liver cirrhosis at the end of the trial, where the remaining viable hepatocytes were separated in a matrix of collagen. [3H1]Thymidine incorporation in hepatic DNA of acetaminophen or oxidized lipid intoxication increased in the early stages of intoxication, indicative of regenerative activity of the liver. Further progression of the cirrhosis inhibited continued liver regeneration and [3H1]thymidine incorporation into hepatic DNA. The cirrhotic liver at this stage failed to regenerate to the original mass upon 75% partial hepatectomy. Therefore, it may be concluded that hepatic necrosis produced by oxidized lipids or by acetaminophen may have similar mechanisms.

Metabolic basis for high paracetamol dosage without hepatic injury: a case study

1. Studies of paracetamol metabolism were performed in a 58-year-old female with rheumatoid arthritis who had consumed 15-20 g paracetamol daily for 5 years without developing liver damage and data were compared with results in seven normal volunteers. 2. After a test dose of 2 g paracetamol, the formation of paracetamol sulphate and glucuronide conjugates detected in plasma from the patient was delayed by around 2 h relative to values in normal volunteers and the proportion of sulphate conjugates excreted in urine was 1.5 to 2 times those in normal volunteers (52% vs 26-35% of dose, respectively). The fractional metabolite clearance of paracetamol to glutathione-derived conjugates (0.28 ml min-1 kg-1) in our patient was > 30% lower than in normal females. 3. A combination of slow paracetamol absorption, enhanced detoxication of paracetamol (by sulphation) and reduced metabolism to potentially cytotoxic metabolites may have reduced the risk of liver damage in this patient. The latter may have reflected pharmacogenetic deficiencies in cytochrome P450 isoenzymes persisting despite chronic alcohol consumption (40-60 g per day) or resulted from inhibition of paracetamol activation by concomitant ingestion of aminophylline.