Long-Term Anticonvulsant Therapy Worsens Outcome in Paracetamol-Induced Fulminant Hepatic Failure

The impact of race and gender on the outcomes of patients with acetaminophen-induced acute liver failure: propensity score-matched analysis of the NIS database

BACKGROUND

Acetaminophen overdose is one of the leading causes of acute liver failure in the USA. In this study, we investigated the impact of race and gender on the hospital outcomes of patients admitted with acetaminophen-induced acute liver failure.

METHODS

From the National Inpatient Sample between the years 2016 and 2019, patients with acetaminophen-induced acute liver failure were selected and stratified based on gender (Male and Female) and race (White, Black and Hispanic). The cases were propensity score-matched to controls (male and Whites) and were compared along the following endpoints: mortality, length of stay, hospitalization costs, and hepatic complications.

RESULTS

Among patients with acetaminophen-induced acute liver failure, females experienced higher rates of mortality (16.60% vs. 11.70%, P = 0.004) and clinical illness, including hypotension (11.80% vs. 7.15%, P = 0.002) and ventilator use (40.80% vs. 30.00%, P < 0.001). When stratified by race, Black patients had longer hospital stays (Black vs. White, 8.76 days vs. 7.46 days, P = 0.03). There were no significant differences in outcomes between Hispanic and White patients. No significant differences in mortality were shown between races.

CONCLUSION

We found that females had a higher rate of mortality and incidence of hepatic encephalopathy compared to males. When stratified by race, Blacks were shown to have longer hospital stay. Females and racial minorities were also affected by special healthcare needs after discharge compared to their male and White cohorts, respectively.

A review: Systematic research approach on toxicity model of liver and kidney in laboratory animals

Therapeutic experiments are commonly performed on laboratory animals to investigate the possible mechanism(s) of action of toxic agents as well as drugs or substances under consideration. The use of toxins in laboratory animal models, including rats, is intended to cause toxicity. This study aimed to investigate different models of hepatotoxicity and nephrotoxicity in laboratory animals to help researchers advance their research goals. The current narrative review used databases such as Medline, Web of Science, Scopus, and Embase and appropriate keywords until June 2021. Nephrotoxicity and hepatotoxicity models derived from some toxic agents such as cisplatin, acetaminophen, doxorubicin, some anticancer drugs, and other materials through various signaling pathways are investigated. To understand the models of renal or hepatotoxicity in laboratory animals, we have provided a list of toxic agents and their toxicity procedures in this review.

The Risk of Drug-Drug Interactions with Paracetamol in a Population of Hospitalized Geriatric Patients

Aims

This study investigates the consumption of paracetamol and the risk of potential drug-drug interactions and assesses the clinical impact hereof in patients admitted to a department of geriatric medicine.

Methods

A retrospective and longitudinal study was conducted in patients who had been receiving paracetamol upon or during hospitalization. The hospital files of the included patients were reviewed, including documentation of concomitant medications, diagnoses, biochemical values, and adverse incidents during admission. These parameters were used as a clinical follow-up when assessing a clinical probability impact of the identified drug-drug interactions.

Results

In total, 104 patients were admitted during the study period. 91 (87.5%) of these (mean age 86 years) received a prescription or were treated with paracetamol. Of these, 10% were evaluated as being at risk of potential drug-drug interactions with paracetamol. Seven of the potential drug-drug interactions were related to treatments with warfarin, one with valsartan and one with phenytoin. Of the nine patients at risk, six did experience either abnormal biochemical values or potential related clinical incidents. Four patients experienced increased INR (range 3.2–4.6), of which one patient suffered from anaemia and one with hematemesis. Two patients experienced increased ALAT/ASAT (55/42 U/I and 87/51 U/I, both females). One experienced hypertension.

Conclusion

A large majority of the patients in this study received treatment with paracetamol. Six patients were evaluated as having abnormal biochemical values or were experiencing clinical incidents during their hospitalization potentially related to the identified potential drug-drug interactions.

Idiosyncratic Drug Reaction: A Rare Mechanism of Acute Tylenol Toxicity

Acetaminophen (APAP) is perhaps the most commonly used drug both inside and outside the hospital due to its relative safety and over-the-counter availability. Despite its safety, it can cause drug-related side effects, especially acute liver injury that can be unpredictable. Additionally, due to its variable, delayed and nonspecific symptomatology, it can pose a significant diagnostic challenge. Due to potential reversibility with an antidote and adverse outcome related to liver failure, timely recognition and treatment is key in suspected toxicity. Here we present a case of a young female who presented for the evaluation of seizure and found to have APAP-related liver failure with only 2 g of APAP taken over two days duration.

Inter-individual and inter-organ variability in the bioactivation of paracetamol by human liver and kidney tissues

Paracetamol (PAR) overdose is associated with massive hepatic injury; it may induce kidney toxicity as well. It is essential to measure organ-specific activities of related CYPs for evaluating the overdose cases. Available HPLC-based methods require high amounts of tissue samples. In order to develop liquid chromatography mass spectrometry (LC-MS)-based methods to process small amounts of human tissues, liver and kidney samples were obtained. Individual microsomes were prepared and incubated with PAR (for quantifying bioactivation), with nifedipine (for measuring CYP3A4 activity) and with p-nitrophenol (for measuring CYP2E1 activity). The small amount of tissue microsomes was sufficient to measure both the formation of NAPQI and the activities of CYP enzymes. Although the sample size in group was relatively low, both NAPQI formation and activity of CYP2E1 were significantly higher in males compared to females in kidney. Considerable variations in the metabolic capacity of individuals were observed for both organs.

Fever in Children: Pearls and Pitfalls

Fever in children is a common concern for parents and one of the most frequent presenting complaints in emergency department visits, often involving non-pediatric emergency physicians. Although the incidence of serious infections has decreased after the introduction of conjugate vaccines, fever remains a major cause of laboratory investigation and hospital admissions. Furthermore, antipyretics are the most common medications administered to children. We review the epidemiology and measurement of fever, the meaning of fever and associated clinical signs in children of different ages and under special conditions, including fever in children with cognitive impairment, recurrent fevers, and fever of unknown origin. While the majority of febrile children have mild, self-resolving viral illness, a minority may be at risk of life-threatening infections. Clinical assessment differs markedly from adult patients. Hands-off evaluation is paramount for a correct evaluation of breathing, circulation and level of interaction. Laboratory markers and clinical prediction rules provide limited help in identifying children at risk for serious infections; however, clinical examination, prudent utilization of laboratory tests, and post-discharge guidance ("safety netting") remain the cornerstone of safe management of febrile children.

Toxicant-Induced Hepatic Injury

The sudden failure of a previously healthy and functioning liver is a dramatic and devastating event. Acute liver failure is the common final pathway of a multitude of conditions and insults, all of which result in massive hepatic necrosis or loss of normal hepatic function. The ensuing multiorgan system failure frequently has a fatal outcome, with mortality rates in most series ranging from approximately 55% to 95% [1]. Acute liver failure (ALF, previously often referred to as fulminant hepatic failure (FHF)) knows no age boundaries, with many cases occurring in those younger than 30 years. Short of excellent intensive care unit (ICU) support and liver transplantation in selected cases, few viable treatment options are available. Over the past few decades, however, survival has been improved by anticipation, recognition, and early treatment of associated complications, as well as the application of prognostic criteria for early identification of patients requiring liver transplantation (along with improvement in the techniques and science of transplantation itself). The etiology of ALF varies from country to country and the incidence change over time. Paracetamol (acetaminophen) has now replaced viral hepatitis as the leading cause of ALF [2]. In a study from London including 310 patients with ALF in the period 1994–2004, 42% of the cases were caused by paracetamol [3], whereas this was only the cause in 2% of 267 patients in Spain from 1992 to 2000 [4]. However, less than 10% of all liver transplants are performed in patients with ALF [5, 6].

The 100 most influential publications in paracetamol poisoning treatment: a bibliometric analysis of human studies

BACKGROUND

Analysis of the most influential publications within paracetamol poisoning treatment can be helpful in recognizing main and novel treatment issues within the field of toxicology. The current study was performed to recognize and describe the most highly cited articles related to paracetamol poisoning treatment.

METHODS

The 100 most highly cited articles in paracetamol poisoning treatment were identified from the Scopus database in November 2015. All eligible articles were read for basic information, including total number of citations, average citations per year, authors' names, journal name, impact factors, document types and countries of authors of publications.

RESULTS

The median number of citations was 75 (interquartile range 56-137). These publications were published between 1974 and 2013. The average number of years since publication was 17.6 years, and 45 of the publications were from the 2000s. A significant, modest positive correlation was found between years since publication and the number of citations among the top 100 cited articles (r = 0.316; p = 0.001). A total of 55 journals published these 100 most cited articles. Nine documents were published in Clinical Toxicology, whereas eight documents were published in Annals of Emergency Medicine. Citations per year since publication for the top 100 most-cited articles ranged from 1.5 to 42.6 and had a mean of 8.5 citations per year and a median of 5.9 with an interquartile range of 3.75-10.35. In relation to the origin of the research publications, they were from 8 countries. The USA had the largest number of articles, 47, followed by the UK and Australia with 38 and nine articles respectively.

CONCLUSIONS

This study is the first bibliometric assessment of the top 100 cited articles in toxicology literature. Interest in paracetamol poisoning as a serious clinical problem continues to grow. Research published in high-impact journals and from high income countries is most likely to be cited in published paracetamol research.

Timescale analysis of a mathematical model of acetaminophen metabolism and toxicity

Acetaminophen is a widespread and commonly used painkiller all over the world. However, it can cause liver damage when taken in large doses or at repeated chronic doses. Current models of acetaminophen metabolism are complex, and limited to numerical investigation though provide results that represent clinical investigation well. We derive a mathematical model based on mass action laws aimed at capturing the main dynamics of acetaminophen metabolism, in particular the contrast between normal and overdose cases, whilst remaining simple enough for detailed mathematical analysis that can identify key parameters and quantify their role in liver toxicity. We use singular perturbation analysis to separate the different timescales describing the sequence of events in acetaminophen metabolism, systematically identifying which parameters dominate during each of the successive stages. Using this approach we determined, in terms of the model parameters, the critical dose between safe and overdose cases, timescales for exhaustion and regeneration of important cofactors for acetaminophen metabolism and total toxin accumulation as a fraction of initial dose.

Acetaminophen-related hepatotoxicity

Acetaminophen (APAP) is the leading worldwide cause of drug overdose and acute liver failure (ALF). Single overdose ingestion and therapeutic misadventure may cause hepatotoxicity. Several factors, such as concomitant alcohol use or abuse, concurrent medications, genetic factors, and nutritional status, can influence the susceptibility and severity of APAP hepatotoxicity. Early manifestations of APAP hepatotoxicity are nonspecific, but require prompt recognition by physicians. Patients with repeated overdose tend to present late, and in such hepatotoxicity may have already evolved. N-acetylcysteine is a very effective antidote when giving within 8 hours, and is also recommended after a presentation of hepatotoxicity and ALF. The prognosis of patients with APAP-induced ALF is better than other causes of ALF. Liver transplantation should be offered to those who are unlikely to survive.

The biochemistry of acetaminophen hepatotoxicity and rescue: a mathematical model

BACKGROUND

Acetaminophen (N-acetyl-para-aminophenol) is the most widely used over-the-counter or prescription painkiller in the world. Acetaminophen is metabolized in the liver where a toxic byproduct is produced that can be removed by conjugation with glutathione. Acetaminophen overdoses, either accidental or intentional, are the leading cause of acute liver failure in the United States, accounting for 56,000 emergency room visits per year. The standard treatment for overdose is N-acetyl-cysteine (NAC), which is given to stimulate the production of glutathione.

METHODS

We have created a mathematical model for acetaminophen transport and metabolism including the following compartments: gut, plasma, liver, tissue, urine. In the liver compartment the metabolism of acetaminophen includes sulfation, glucoronidation, conjugation with glutathione, production of the toxic metabolite, and liver damage, taking biochemical parameters from the literature whenever possible. This model is then connected to a previously constructed model of glutathione metabolism.

RESULTS

We show that our model accurately reproduces published clinical and experimental data on the dose-dependent time course of acetaminophen in the plasma, the accumulation of acetaminophen and its metabolites in the urine, and the depletion of glutathione caused by conjugation with the toxic product. We use the model to study the extent of liver damage caused by overdoses or by chronic use of therapeutic doses, and the effects of polymorphisms in glucoronidation enzymes. We use the model to study the depletion of glutathione and the effect of the size and timing of N-acetyl-cysteine doses given as an antidote. Our model accurately predicts patient death or recovery depending on size of APAP overdose and time of treatment.

CONCLUSIONS

The mathematical model provides a new tool for studying the effects of various doses of acetaminophen on the liver metabolism of acetaminophen and glutathione. It can be used to study how the metabolism of acetaminophen depends on the expression level of liver enzymes. Finally, it can be used to predict patient metabolic and physiological responses to APAP doses and different NAC dosing strategies.

Does cytochrome P450 liver isoenzyme induction increase the risk of liver toxicity after paracetamol overdose?

Paracetamol (acetaminophen, N-acetyl-p-aminophenol, 4-hydroxyacetanilide) is the most common cause of acute liver failure in developed countries. There are a number of factors which potentially impact on the risk of an individual developing hepatotoxicity following an acute paracetamol overdose. These include the dose of paracetamol ingested, time to presentation, decreased liver glutathione, and induction of cytochrome P450 (CYP) isoenzymes responsible for the metabolism of paracetamol to its toxic metabolite N-acetyl-p-benzoquinoneimine (NAPQI). In this paper, we review the currently published literature to determine whether induction of relevant CYP isoenzymes is a risk factor for hepatotoxicity in patients with acute paracetamol overdose. Animal and human in vitro studies have shown that the CYP isoenzyme responsible for the majority of human biotransformation of paracetamol to NAPQI is CYP2E1 at both therapeutic and toxic doses of paracetamol. Current UK treatment guidelines suggest that patients who use a number of drugs therapeutically should be treated as “high-risk” after paracetamol overdose. However, based on our review of the available literature, it appears that the only drugs for which there is evidence of the potential for an increased risk of hepatotoxicity associated with paracetamol overdose are phenobarbital, primidone, isoniazid, and perhaps St John’s wort. There is no evidence that other drugs often quoted as increasing risk, such as carbamazepine, phenytoin, primidone, rifampicin, rifabutin, efavirenz, or nevirapine, should be considered risk factors for hepatotoxicity in patients presenting with acute paracetamol overdose.

A review of the hepatotoxicity of paracetamol at therapeutic or near-therapeutic dose levels, with particular reference to alcohol abusers

The number of published reports associating hepatotoxicity with paracetamol ingestion at therapeutic or near-therapeutic dose levels is small but is, nevertheless, suggestive of a relationship. There is however, mounting evidence that certain groups of patients, such as alcohol-dependent people, patients receiving enzyme-inducing drugs (particularly anti-convulsant and anti-tuberculosis medications) as well as those with certain infectious diseases, are rendered more susceptible to paracetamol-induced hepatotoxicity. Seventy-four case reports where therapeutic or near-therapeutic doses of paracetamol resulted in hepatic injury are reviewed and factors and mechanisms which might explain this apparently increased vulnerability to damage are discussed.

Acetaminophen hepatotoxicity and acute liver failure

Acetaminophen-induced hepatotoxicity is a common consequence of acetaminophen overdose and may lead to acute liver failure (ALF). Currently acetaminophen is the most common cause of ALF in both United States and United Kingdom, with a trend to increasing incidence in the United States. N-acetylcysteine is the most effective drug to prevent progression to liver failure with acetaminophen hepatotoxicity. Liver transplantation is the only definitive therapy that will significantly increase the chances of survival for advanced ALF. This communication reviews current information regarding causes and management of acetaminophen-induced hepatotoxicity and ALF.

Acetaminophen-induced nephrotoxicity: pathophysiology, clinical manifestations, and management

Acetaminophen-induced liver necrosis has been studied extensively, but the extrahepatic manifestations of acetaminophen toxicity are currently not described well in the literature. Renal insufficiency occurs in approximately 1-2% of patients with acetaminophen overdose. The pathophysiology of renal toxicity in acetaminophen poisoning has been attributed to cytochrome P-450 mixed function oxidase isoenzymes present in the kidney, although other mechanisms have been elucidated, including the role of prostaglandin synthetase and N-deacetylase enzymes. Paradoxically, glutathione is considered an important element in the detoxification of acetaminophen and its metabolites; however, its conjugates have been implicated in the formation of nephrotoxic compounds. Acetaminophen-induced renal failure becomes evident after hepatotoxicity in most cases, but can be differentiated from the hepatorenal syndrome, which may complicate fulminant hepatic failure. The role of N-acetylcysteine therapy in the setting of acetaminophen-induced renal failure is unclear. This review will focus on the pathophysiology, clinical features, and management of renal insufficiency in the setting of acute acetaminophen toxicity.

CASE

A 47-year-old female was found lethargic at home and brought by ambulance to an emergency department. History from family members suggested an inadvertent acetaminophen overdose, and she had last been seen a few hours earlier. She reportedly ingested 18 tablets of 500 mg acetaminophen (APAP) over the previous two days because she had run out of her prescription pain medication. Her past medical history was significant for fibromyalgia, arthritis, and a prior gastric bypass procedure. She had no history of alcohol abuse or renal insufficiency. She was lethargic. Vital signs: BP 128/96 mmHg, pulse 112/min, respirations 32/min; pulse oximetry 98% on 2L nasal cannula oxygen. Laboratory studies: BUN 9 mg/dL, creatinine 0.9 mg/dl, acetaminophen 12 mcg/mL, AST 5409 u/L and ALT 1085 u/L. A urinalysis was negative for blood with trace protein and ketones. A urine drug screen was positive for marijuana and opioid metabolites. At the initial hospital, she was treated with N-acetylcysteine (NAC) orally. Subsequently, she developed fulminant hepatic failure with elevated transaminases, hypoglycemia, and coagulopathy (Tables 1A and 1B). She was transferred to our facility two days after initial presentation for liver transplant evaluation. At that time, her APAP level was 2.0 mg/L. Oral NAC therapy was continued after transfer. The patient's liver function subsequently improved and she ultimately did not require transplantation. She did develop acute renal failure during the course of her hospitalization, with a creatinine of 2.3 mg/dL on transfer, which increased to 8.1 mg/dL nine days later (approximately 11-13 days post-ingestion). Medical toxicology was consulted by the intensive care unit team to address whether this was acetaminophen-induced renal failure and if there was a role for NAC in this setting.

Hepatotoxicity associated with antiepileptic drugs

BACKGROUND

Drug-induced liver injury associated with antiepileptic drugs (AED) is well recognized. The frequency of the most common AED is rare but the consequences can be very serious leading to death or liver transplantation due to acute liver failure induced by these drugs.

CLINICAL FEATURES

Hypersensitivity features are found in more than 70% of patients with phenytoin-induced liver injury, whereas this is only observed in 30% of carbamazepine-associated hepatotoxicity and very rarely with valproate (VPA)-induced liver injury.

PATHOPHYSIOLOGY

The underlying mechanisms behind hepatotoxicity induced by AED are not clear. Reactive metabolites from AED can, in some cases, lead to direct cytotoxicity and liver cell necrosis, whereas in other cases this may lead to neoantigen formation inducing immunoallergic mechanisms.

TREATMENT

No specific therapy is of proved value in severe hepatotoxicity due to AED. However, N-acetylcystein is an appropriate treatment in patients with clinically significant liver injury due to phenytoin and carbamazepine. In patients with VPA-associated liver injury, carnitine that is an important co-factor in the mitochondrial beta-oxidation of fatty acids is the recommended treatment. Early referral of patients with severe liver reactions and coagulopathy to liver transplant centers before encephalopathy can be the difference between liver transplantation and death.

The poisoned child in the pediatric intensive care unit

Acutely poisoned children remain a common problem facing pediatricians working in acute care medicine in the United States and worldwide. The management of such children continues to be challenging, and their care has evolved throughout the years. The concept of gastric decontamination in acute poisoning has significantly changed over the past 10 years, and many of the previously used techniques have been abandoned or fallen out of favor for lack of evidence to their benefit or unacceptable serious risks and side effects. Supportive care continues to be the cornerstone in managing most poisoned children. Only a few patients benefit from antidotes or specific interventions.

Acetaminophen hepatotoxicity

Acetaminophen is a commonly used antipyretic and analgesic agent. It is safe when taken at therapeutic doses; however, overdose can lead to serious and even fatal hepatotoxicity. The initial metabolic and biochemical events leading to toxicity have been well described, but the precise mechanism of cell injury and death is unknown. Prompt recognition of overdose, aggressive management, and administration of N-acetylcysteine can minimize hepatotoxicity and prevent liver failure and death. Liver transplantation can be lifesaving for those who develop acute liver failure.

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.

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).

Acetaminophen Poisoning

Acetaminophen (acetyl-para-amino-phenol or APAP), an antipyretic and analgesic, is a common component in hundreds of over-the-counter and prescription medications. The wide usage of this drug results in many potentially toxic exposures. It is therefore critical for the clinician to be comfortable with the diagnosis and treatment of APAP toxicity. Prompt recognition of APAP overdose and institution of appropriate therapy are essential to preventing morbidity and mortality.

Updates on acetaminophen toxicity

APAP is likely to remain a common toxic exposure and continue to cause significant morbidity and mortality. To minimize the harm to patients, it is necessary for the clinician to be aware of the current diagnostic and therapeutic management of APAP poisoning. Despite the bulk of literature on APAP, management strategies are likely to continue to change as more studies are conducted to improve our understanding of nonacute ingestions and the role of prognostic markers in defining those most at risk for life-threatening hepatotoxicity.

Potentiation of acetaminophen hepatotoxicity by phenytoin, leading to liver transplantation

We report the case of a 22-year-old man who developed fulminant hepatic failure 3 days after an intentional acetaminophen overdose. The patient had a history of a seizure disorder for which he was taking phenytoin. The acetaminophen level at presentation was in the "nontoxic" range. Emergent liver transplantation was performed 4 days after the ingestion. This is the first reported case of successful liver transplantation for acetaminophen-induced fulminant hepatic failure in the setting of phenytoin therapy.

Phenobarbital and Phenytoin Increased Acetaminophen Hepatotoxicity Due to Inhibition of UDP-Glucuronosyltransferases in Cultured Human Hepatocytes

Here we present a preclinical model to assess drug-drug interactions due to inhibition of glucuronidation. Treatment with the antiepileptics phenobarbital (PB) or phenytoin (PH) has been associated with increased incidence of acetaminophen (APAP) hepatotoxicity in patients. In human hepatocytes, we found that the toxicity of APAP (5 mM) was increased by simultaneous treatment with phenobarbital (2 mM) or phenytoin (0.2 mM). In contrast, pretreatment with PB for 48 h prior to APAP treatment did not increase APAP toxicity unless both drugs were present simultaneously. Cells treated with APAP in combination with PB or PH experienced decreases in protein synthesis as early as 1 h, ultrastructural changes by 24 h, and release of liver enzymes by 48 h. Toxicity correlated with inhibition of APAP glucuronidation. PB or PH also inhibited APAP glucuronidation in rat and human liver microsomes and expressed human UGT1A6, 1A9, and 2B15. As with intact hepatocytes, PB and PH were neither hydroxylated nor glucuronidated, suggesting the direct inhibition of UGTs. Our findings suggest that, in multiple drug therapy, an inhibitory complex between UGT and one of the drugs can lead to decreased glucuronidation and increased systemic exposure and toxicity of a coadministered drug.

Drug Interactions with Paracetamol

Paracetamol (acetaminophen) is one of the most commonly used analgesic antipyretic drugs worldwide, and it is widely available by prescription and over the counter (OTC). Fortunately, few clinically significant drug interactions have been documented. There is probable potentiation of hepatotoxicity following an overdose from the paracetamol metabolite NAPQI by enzyme-inducing drugs. There is considerable controversy regarding the possible interaction with warfarin in its potential to increase its anticoagulant effects because of discrepancies between observational studies and those in healthy volunteers. Otherwise, no serious adverse drug interactions with therapeutic doses of paracetamol have been confirmed in humans. Because the absorption of paracetamol is so dependent on gastric emptying, other drugs that alter gastric emptying can change its pharmacokinetics; but this would not cause serious adverse effects. Although animal experiments have demonstrated that many compounds can modify paracetamol hepatotoxicity, these are unlikely to be important at therapeutic doses.

The impact of current tobacco use on the outcome of paracetamol poisoning

BACKGROUND

Tobacco smoke contains a number of substances that are capable of inducing cytochrome P450. Consequently, current tobacco use may enhance the hepatotoxicity from a paracetamol overdose by increasing the oxidative metabolism of paracetamol.

AIM

To evaluate, by multivariate analysis, the effect of current tobacco use on the morbidity and mortality from paracetamol-induced hepatotoxicity.

METHODS

A retrospective study was carried out on the basis of the hospital charts of 602 patients admitted with single-dose paracetamol poisoning for whom information on current tobacco use was available.

RESULTS

In patients admitted with paracetamol poisoning, the rate of current daily tobacco use of 70% (424 of 602 patients) was considerably higher than the rate of 31% in the background population (chi-squared test: P < 0.0001). Current tobacco use was an independent risk factor for the development of hepatic encephalopathy (odds ratio, 2.68; 95% confidence interval, 1.28-5.62) and mortality (odds ratio, 3.64; 95% confidence interval, 1.23-10.75). Current tobacco use was independently associated with high peak values of alanine transaminase and the international normalized ratio.

CONCLUSIONS

Current tobacco use was very frequent in patients admitted with paracetamol poisoning. It was an independent risk factor of severe hepatotoxicity, acute liver failure and death following paracetamol overdose.

Paracetamol poisoning: Which nomogram should we use?

OBJECTIVES

To determine the type of paracetamol nomograms used in Australasian EDs. To review the literature to determine the evidence base for existing nomograms.

METHODS

A cross sectional descriptive study via postal survey of all Australasian EDs accredited for specialist emergency medicine training by the Australasian College for Emergency Medicine (ACEM). A literature review using Knowledge Finder search engine was employed.

RESULTS

The response rate was 87%. The most commonly used nomogram had a four-hour treatment level of 1300 mumol/L (69%). A total of 22% of respondents used a four-hour treatment level of 1000 mumol/L. Two departments (3%) treated all patients above the 660 mumol/L line. Eleven departments (15%) did not have a treatment line below 1300 mumol/L.

CONCLUSION

Practice varies in Australasian EDs. Patients with paracetamol levels below the 1300 mumol/L have been reported in the literature to develop hepatotoxicity, and deaths have been documented. N-acetylcysteine is extremely safe when used in the recommended dosages.

Chronic acetaminophen toxicity: a case report and review of the literature

Acetaminophen is one of the most frequently used medications in the United States. While usual dosing of acetaminophen is considered harmless, both acute and chronic overdoses can be fatal. The majority of reported cases of chronic acetaminophen toxicity in adults occur in chronic alcohol abusers, patients taking P450-inducing medications, or following massive dosing. We describe a case of toxic hepatitis free of the aforementioned risk factors associated with chronic ingestion of moderately excessive doses of acetaminophen. Our patient ingested approximately 5.0 to 6.5 g of acetaminophen daily for 6 to 8 weeks via multiple medications. The inclusion of acetaminophen in numerous medications combined with the frequency of use of acetaminophen necessitates an increased concern for not only acute but also chronic acetaminophen toxicity.

The effect of regular medication on the outcome of paracetamol poisoning

BACKGROUND

Patients admitted with paracetamol overdose frequently receive one or more types of regular medication that may affect the outcome of the paracetamol intoxication.

AIM

To describe the use of regular medication in patients with paracetamol poisoning and to evaluate its effects on morbidity and mortality.

METHODS

Seven hundred and thirty-seven consecutive patients admitted with paracetamol poisoning were studied and the use of regular medication was recorded. The relative risk of hepatic encephalopathy, death or liver transplantation, severe hepatic dysfunction and severe hepatocellular injury was evaluated by multivariate analysis.

RESULTS

Regular medication was received by 332 patients (45%). Medication with benzodiazepines (105 cases), antidepressants (100 cases), neuroleptics (75 cases), paracetamol (58 cases), oral contraceptives (51 cases), beta-agonists (40 cases), opioid analgesics (32 cases) and anticonvulsants (27 cases) predominated. Regular medication with opioid analgesics was associated with a high incidence of hepatic dysfunction (odds ratio, 5.39; 95% confidence interval, 1.13-25.8). No significant findings were demonstrated for benzodiazepines, antidepressants, neuroleptics, paracetamol, oral contraceptives, beta-agonists or anticonvulsants in the multivariate analysis.

CONCLUSIONS

Regular medication with psychotropic medication, analgesics, oral contraceptives, beta-agonists or anticonvulsants was frequent in patients admitted with paracetamol poisoning. Medication with opioid analgesics was associated with a significantly increased incidence of hepatic dysfunction, whereas the other medications did not appear to affect the outcome of the paracetamol intoxication.

Acetaminophen hepatotoxicity: the first 35 years

The acetaminophen nomogram including its uses and limitations is discussed as well as the development of the N-acetylcysteine protocol. While it has taken many years to elucidate the genetic variability and true multiplicity of the cytochrome P450 "mixed function oxidase system" many publications early on looked at the enzyme system as a single entity. Numerous articles indicated that barbiturates, anticonvulsants, and others could induce "P450" and add to the toxicity of acetaminophen. It rapidly became apparent that just because "P450" was induced when measured as a whole, not all other substrates would have changed metabolic activity. The role of diet and ethanol induction and inhibition on CYP2E1, the enzyme of greatest interest for acetaminophen is multifaceted. The lack of enhancement of acetaminophen toxicity by phenytoin and in fact, the potential for reduction of toxicity with that agent is a good example of the evolution of our knowledge. Further complicating our understanding is the introduction of misleading terms such as "therapeutic misadventure" and other expressions of molecular intent. A critical understanding of the literature makes it clear that therapeutic doses of acetaminophen either alone or in the presence of inducers do not produce toxicity. While the community of clinical toxicologists is small, it needs to be more aggressive in making sure that physicians from other specialties and non-clinical toxicology colleagues understand the significance and implications of this science.

Concomitant overdosing of other drugs in patients with paracetamol poisoning

AIMS

Paracetamol is frequently involved in intended self-poisoning, and concomitant overdosing of other drugs is commonly reported. The purpose of the study was to investigate further concomitant drug overdose in patients with paracetamol poisoning and to evaluate its effects on the outcome of the paracetamol intoxication.

METHODS

Six hundred and seventy-one consecutive patients admitted with paracetamol poisoning were studied and concomitant drug intake was recorded. The relative risk of hepatic encephalopathy, death or liver transplantation, hepatic dysfunction, liver cell damage, and renal dysfunction associated with concomitant overdosing of other drugs was evaluated by multivariate analysis.

RESULTS

Concomitant drug overdose was found in 207 patients (31%, 95% confidence interval [CI] 27, 34%). Concomitant overdosing of benzodiazepines (99 cases), opioid analgesics (38 cases), acetylsalicylic acid (33 cases), and NSAID (32 cases) predominated. Concomitant benzodiazepine overdose was an independent risk factor in the development of hepatic encephalopathy (odds ratio [OR] 1.91; CI 1.00, 3.65) and renal dysfunction (OR 1.81; CI 1.00, 3.22). Concomitant overdosing of opioid analgesics was a protective factor in the development of hepatic encephalopathy (OR 0.26; CI 0.07, 0.96). Concomitant acetylsalicylic acid overdose was a risk factor in the development of hepatic encephalopathy (OR 4.87; CI 1.52, 15.7) and death or liver transplantation (OR 6.04; CI 1.69, 21.6). A tendency towards a more favourable outcome was observed in patients with concomitant NSAID overdose.

CONCLUSIONS

Concomitant overdosing of benzodiazepines or analgesics is frequent in patients admitted with paracetamol poisoning. Concomitant benzodiazepine or acetylsalicylic acid overdose was associated with more severe toxicity, whereas concomitant overdosing of opioid analgesics was associated with less toxicity.

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.

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.

Acetaminophen toxicity in children

Acetaminophen is widely used in children, because its safety and efficacy are well established. Although the risk of developing toxic reactions to acetaminophen appears to be lower in children than in adults, such reactions occur in pediatric patients from intentional overdoses. Less frequently, acetaminophen toxicity is attributable to unintended inappropriate dosing or the failure to recognize children at increased risk in whom standard acetaminophen doses have been administered. Because the symptoms of acetaminophen intoxication are nonspecific, the diagnosis and treatment of acetaminophen intoxication are more likely to be delayed in unintentional cases of toxicity. This statement describes situations and conditions that may contribute to acetaminophen toxicity not associated with suicidal intentions.

Chronic acetaminophen overdosing in children: risk assessment and management

Acetaminophen is currently the pediatric analgesic and antipyretic of choice. Although children appear to tolerate single, high-dose ingestions well, the literature is replete with reports of significant morbidity and mortality after repeated supra-therapeutic dosing. Proposed risk factors for injury with chronic use include age, total dose, duration, presence of intercurrent febrile illness, starvation, co-administration of cytochrome P450-inducing drugs, underlying hepatic disease, and unique genetic makeup. Evaluation of these children should include serum acetaminophen concentration, prothrombin time, and serum bilirubin and transaminase concentrations. The Rumack-Mathew nomogram should not be used to estimate the risk of hepatotoxicity in cases of chronic ingestion. Based on history, clinical examination, and laboratory findings, patients may be placed in three categories: those without hepatic injury and with no residual acetaminophen to be metabolized, those without injury but with some acetaminophen to be metabolized, and those with hepatotoxicity. Those without injury and no residual acetaminophen need not be treated or followed. Patients with hepatotoxicity or potential for hepatotoxicity based on residual acetaminophen should be treated with N-acetylcysteine. Most importantly, because so many parents are unaware of the potential risk of inappropriate dosing, education is the key to preventing future cases.

[Clinical evaluation of the efficacy of the paracetamol and caffeine combination in the treatment of tension headache]

Tension type headache in both its forms, episodic and chronic, is the most common type of headache experienced by the population. The headache attack or the prevention of new crises may be treated with pharmacological as well as non-pharmacological measures. This study included 5,490 patients from out-patient clinics and medical offices covering various regions of Brazil. Approximately 95% of the subjects had episodic tension type headache, while 5% had chronic tension type headache. The majority of the patients presented with crisis of moderate intensity (62.19%). In 5,419 patients a tension type headache crisis was treated with acetaminophen 1000 mg and caffeine 130 mg. In 93.98%, onset of relief occurred within 2 hours of taking the medication. In 77.61%, complete reversion of the crisis occurred within 2 hours. Good/excellent efficacy ratings were achieved in 61.93%/37.80% of the cases according to the physician's assessment and in 48.51%/40.29% according to the patients' assessment. Adverse events, commonly gastrointestinal manifestations, were reported by 5.57% of the patients. This is a Brazilian study of the efficacy and safety of the combined use of acetaminophen-caffeine for the treatment of tension type headache.

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.

A dose-dependent delayed hypersensitivity reaction to acetaminophen after repeated acetaminophen intoxications

We report a case of a 29-year-old woman with a borderline personality disorder who presented with intentional substantial acetaminophen (paracetamol) overdosage on nine occasions during a period of 21 months. In most cases, the patient presented at the hospital within 4 h after ingestion and was treated with gastric lavage, activated charcoal, laxatives and intravenous N-acetylcysteine. During the sixth overdosage the patient developed a rash on her chest and shoulders which was considered an anaphylactoid reaction to N-acetylcysteine. Therefore she was treated with oral methionine subsequently, but developed the rash again. The rash was then ascribed to the repeated high-doses of acetaminophen and treatment with N-acetylcysteine was reinstituted. This case shows that when an anaphylactoid reaction occurs after an acetaminophen overdose and treatment with N-acetylcysteine, acetaminophen must also be taken into account as the cause of the anaphylactoid reaction before effective therapy with N-acetylcysteine is withheld.