Paracetamol overdose: an evidence based flowchart to guide management

The mechanism of NLRP3 inflammasome activation and its pharmacological inhibitors

NLRP3 (NOD-, LRR-, and pyrin domain-containing protein 3) is a cytosolic pattern recognition receptor (PRR) that recognizes multiple pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Once activated, NLRP3 initiates the inflammasome assembly together with the adaptor ASC and the effector caspase-1, leading to caspase-1 activation and subsequent cleavage of IL-1β and IL-18. Aberrant NLRP3 inflammasome activation is linked with the pathogenesis of multiple inflammatory diseases, such as cryopyrin-associated periodic syndromes, type 2 diabetes, non-alcoholic steatohepatitis, gout, and neurodegenerative diseases. Thus, NLRP3 is an important therapeutic target, and researchers are putting a lot of effort into developing its inhibitors. The review summarizes the latest advances in the mechanism of NLRP3 inflammasome activation and its pharmacological inhibitors.

Urgent need to standardize labelling of acetaminophen-paediatric liquid drug products in Saudi Arabia

In this study, dosing instructions in package inserts of all 12 paediatric liquid acetaminophen products registered in pharmacies in the Kingdom of Saudi Arabia were analysed to determine the potential for administering a supratherapeutic dose of acetaminophen. Doses in millilitres were calculated as mg/kg for four age groups: three months old, one year old, six years old, and twelve years old, and based on the 3rd, 50th, and 75th weight percentiles of each age group. Acetaminophen concentrations in the products varied, and only two products included Arabic language instructions. The dosing instructions in eight products included an age overlap. The most affected age group was the 1-year-old group, with 21 supratherapeutic doses across all 12 products. The least affected age group was the 12-year-old group, with 8 supratherapeutic doses in total. The absence of strict supervision and monitoring of labels of paediatric liquid acetaminophen products increases the risk of liver toxicity in children. Therefore, we call for an immediate standardisation of all dosing instructions regarding the dose per weight and the inclusion of instructions in Arabic.

Drugs and the liver

The liver is a major organ with multiple functions. A number of drugs are metabolized by the liver during phase 1 and 2 reactions which include complex processes involving cytochrome P450 enzymes. Genetic and acquired variability in cytochrome P450 activity may have profound effects on pharmacokinetics. Additionally, drugs can also modify how the liver functions and cause dysfunction or even failure of the organ both by a direct effect on the liver or by alteration in liver blood flow. It is important to recognize the signs and symptoms of liver failure in patients and identify possible causes including drug interactions. Furthermore, once a patient has been recognized to be suffering with liver dysfunction or failure drug choice and dosing regime will need to be rationalized.

Paracetamol overdose can have severe and life threatening consequences for patients due to its effect on liver function. It is the leading cause of acute liver failure in the UK,¹ Correct and early management is crucial and will be discussed within this article.

Dried blood microsamples: Suitable as an alternative matrix for the quantification of paracetamol-protein adducts?

Paracetamol (acetaminophen, APAP) is the most frequently used analgesic drug worldwide. However, patients in several specific populations can have an increased exposure to toxic APAP metabolites. Therefore, APAP-protein adducts have been proposed as an alternative marker for the assessment of APAP intoxications and as an effective tool to study and steer APAP treatment in patients with an increased risk of APAP-induced liver damage. These adducts have been determined in plasma or serum as a matrix. Blood microsampling allows the determination of a variety of analytes, including protein adducts, in a drop of blood, facilitating convenient follow-up of patients in a home-sampling context, as well as repeated sampling of pediatric patients. We therefore evaluated the use of blood-based volumetric microsamples for the quantification of APAP-protein adducts. Quantitative methods for the determination of APAP-protein adducts in dried blood and dried plasma volumetric absorptive microsamples were developed and validated. Also a preliminary evaluation of pediatric patient dried blood microsamples was conducted. Method validation encompassed the evaluation of selectivity, carry over, calibration model, accuracy and precision, matrix effect, recovery and the effect of the hematocrit on the recovery, dilution integrity, and stability. All pre-set acceptance criteria were met, except for stability. Spiking of blank blood with APAP revealed a concentration-dependent ex vivo formation of APAP-protein adducts, resulting in a response for the measurand APAP-Cys, with an apparent role for the red blood cell fraction. Analysis of authentic samples, following intake of APAP at therapeutic dosing, revealed much higher APAP-Cys concentrations in dried blood vs. dried plasma samples, making interpretation of the results in the context of published intervals difficult. In addition, in contrast to what was observed during method validation, the data obtained for the patient samples showed a high and unacceptable variation. We conclude that, for a combination of reasons, dried blood is not a suitable matrix for the quantification of APAP-protein adducts via the measurement of the APAP-Cys digestion product. The collection of plasma or serum, either in the form of a liquid sample or a dried microsample for this purpose is advised.

c-Jun NH2 -Terminal Protein Kinase Phosphorylates the Nrf2-ECH Homology 6 Domain of Nuclear Factor Erythroid 2-Related Factor 2 and Downregulates Cytoprotective Genes in Acetaminophen-Induced Liver Injury in Mice

BACKGROUND AND AIMS

Acetaminophen (APAP) overdose induces severe liver injury and hepatic failure. While the activation of c-Jun NH₂ -terminal kinase (JNK) has been implicated as a mechanism in APAP-induced liver injury, the hepatic defense system controlled by nuclear factor erythroid 2-related factor 2 (Nrf2) plays a central role in the mitigation of APAP toxicity. However, the link between the two signaling pathways in APAP-induced liver injury (AILI) remains unclear.

APPROACH AND RESULTS

In this study, we demonstrated that the activation of JNK in mouse liver following exposure to APAP was correlated with the phosphorylation of Nrf2 and down-regulation of the antioxidant response element (ARE)-driven genes, NAD(P)H:quinone dehydrogenase 1, glutathione S-transferase α3, glutathione S-transferase M1, glutathione S-transferase M5, and aldo-keto reductase 1C. The JNK inhibitor, SP600125, or knockdown of JNK by infection of adenovirus expressing JNK small interfering RNA, ameliorated the APAP induced liver toxicity, and inhibited the phosphorylation of Nrf2 and down-regulation of detoxifying enzymes by stabilizing the transcription factor. Mechanistically, JNK antagonized Nrf2- and ARE-driven gene expression in a Kelch-like ECH-associated protein 1-independent manner. Biochemical analysis revealed that phosphorylated JNK (P-JNK) directly interacted with the Nrf2-ECH homology (Neh) 1 domain of Nrf2 and phosphorylated the serine-aspartate-serine motif 1 (SDS1) region in the Neh6 domain of Nrf2.

CONCLUSIONS

Mass spectrometric analysis identified serine 335 in the SDS1 region of mNrf2 as the major phosphorylation site for modulation of Nrf2 ubiquitylation by P-JNK. This study demonstrates that Nrf2 is a target of P-JNK in AILI. Our finding may provide a strategy for the treatment of AILI.

Drug-Induced Liver Injury in the Setting of Analgesic Use

No professional society has created guidelines to aid clinicians in the management of analgesics in the setting of hepatic injury. Acetaminophen overdose is the most common cause of acute liver failure in the United States. In the setting of acetaminophen toxicity, N-acetylcysteine remains the standard of care. Other analgesics including nonsteroidal antiinflammatory drugs, opiates, tricyclic antidepressants, and anticonvulsants rarely cause liver injury.

Case Report: Paracetamol Poisoning in a 2-Year-Old Child – from International Overview to the Role of the Hong Kong Poison Information Centre

We report a 2-year-old girl suffering from acute liver failure as a result of paracetamol poisoning. The child successfully recovered after intensive care. We performed literature search for the past decade and found that the pathophysiological response in the child was different from that of the adult. Despite paracetamol poisoning being one of the most common poisonings in the world, there is still no consensus in the treatment protocol. Hence the role of the Hong Kong Poison Information Centre is briefly discussed.

Paracetamol clinical dosing routine leads to paracetamol underexposure in an adult severely ill sub-Saharan African hospital population: a drug concentration measurement study

Background

Hospitals in sub-Saharan Africa (SSA) continue to receive high numbers of severely ill (HIV-infected) patients with physical pain that may suffer from hepatic and renal dysfunction. Paracetamol is widely used for pain relief in this setting but it is unknown whether therapeutic drug concentrations are attained. The aim of this study was to assess the occurrence of therapeutic, sub-therapeutic and toxic paracetamol concentrations in SSA adult hospital population.

Methods

In a cross-sectional study, plasma paracetamol concentrations were measured in patients with an oral prescription in a referral hospital in Mozambique. From August to November 2015, a maximum of four blood samples were drawn on different time points for paracetamol concentration measurement and biochemical analysis. Study endpoints were the percentage of participants with therapeutic (≥ 10 and ≤ 20 mg/L), sub-therapeutic (< 10 mg/L) and toxic (> 75 mg/L) concentrations.

Results

Seventy-six patients with a median age of 37 years, a body mass index of 18.2, a haemoglobin concentration of 10.3 g/dL and an albumin of 29 g/L yielded 225 samples. 13.4% of participants had one or more therapeutic paracetamol concentrations. 86.6% had a sub-therapeutic concentration at all time points and 70.2% had two or more concentrations below the lower limit of quantification. No potentially toxic concentrations were found.

Conclusions

Routine oral dosing practices in a SSA hospital resulted in substantial underexposure to paracetamol. Palliation is likely to be sub-standard and oral palliative drug pharmacokinetics and dispensing procedures in this setting need further investigation.

Paracetamol: overdose-induced oxidative stress toxicity, metabolism, and protective effects of various compounds in vivo and in vitro

Paracetamol (APAP) is one of the most widely used and popular over-the-counter analgesic and antipyretic drugs in the world when used at therapeutic doses. APAP overdose can cause severe liver injury, liver necrosis and kidney damage in human beings and animals. Many studies indicate that oxidative stress is involved in the various toxicities associated with APAP, and various antioxidants were evaluated to investigate their protective roles against APAP-induced liver and kidney toxicities. To date, almost no review has addressed the APAP toxicity in relation to oxidative stress. This review updates the research conducted over the past decades into the production of reactive oxygen species (ROS), reactive nitrogen species (RNS), and oxidative stress as a result of APAP treatments, and ultimately their correlation with the toxicity and metabolism of APAP. The metabolism of APAP involves various CYP450 enzymes, through which oxidative stress might occur, and such metabolic factors are reviewed within. The therapeutics of a variety of compounds against APAP-induced organ damage based on their anti-oxidative effects is also discussed, in order to further understand the role of oxidative stress in APAP-induced toxicity. This review will throw new light on the critical roles of oxidative stress in APAP-induced toxicity, as well as on the contradictions and blind spots that still exist in the understanding of APAP toxicity, the cellular effects in terms of organ injury and cell signaling pathways, and finally strategies to help remedy such against oxidative damage.

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.

Recent updates on acetaminophen hepatotoxicity: the role of nrf2 in hepatoprotection

Acetaminophen (APAP) known as paracetamol is the main ingredient in Tylenol, which has analgesic and anti-pyretic properties. Inappropriate use of APAP causes major morbidity and mortality secondary to hepatic failure. Overdose of APAP depletes the hepatic glutathione (GSH) rapidly, and the metabolic intermediate leads to hepatocellular death. This article reviews the mechanisms of hepatotoxicity and provides an overview of current research studies. Pharmacokinetics including metabolism (activation and detoxification), subsequent transport (efflux)-facilitating excretion, and some other aspects related to toxicity are discussed. Nuclear factor erythroid 2-related factor 2 (Nrf2)-regulated gene battery plays a critical role in the multiple steps associated with the mitigation of APAP toxicity. The role of Nrf2 as a protective target is described, and potential natural products inhibiting APAP toxicity are outlined. This review provides an update on the mechanism of APAP toxicity and highlights the beneficial role of Nrf2 and specific natural products in hepatoprotection.

Treating acetaminophen overdose: thresholds, costs and uncertainties

The United Kingdom's Medicines and Healthcare Products Regulatory Agency (MHRA) modified the indications for N-acetylcysteine therapy of acetaminophen (paracetamol) overdose in September 2012. The new treatment threshold line was lowered to 100 mg/L (662 μmol/L) for a 4 hours acetaminophen concentration from the previous 200 mg/L (1325 μmol/L). This decision has the potential to substantially increase overall costs associated with acetaminophen overdose with unclear benefits from a marginal increase in patients protected from hepatotoxicity, fulminant hepatic failure, death, or transplant. Changing the treatment threshold for acetaminophen overdose also implies that ingestion amounts previously thought not to require acetaminophen concentration measurements would need to be revised. As a result, more individuals will be sent to hospitals in order that everyone with a predicted 4 hours concentration above the 100 mg/L line will have concentrations measured and potentially be treated with N-acetylcysteine. Before others consider adopting this new treatment guideline, formal cost-effectiveness analyses need to be performed to define the appropriate thresholds for referral and treatment.

Research priorities in biomarkers and surrogate end-points

Ideal tests of the effects of therapeutic interventions measure the desired outcomes; however, the desired outcomes are not always easily measured or may be long-term objectives. Biomarkers and surrogate end-points are often cheaper and easier to measure and can be measured over a shorter time span. They can be used in screening, diagnosing, staging, and monitoring diseases, in monitoring responses to interventions, and in various aspects of drug discovery and development. They can be extrinsic to the body or intrinsic, and can relate to any point in the pharmacological chain, at the molecular, cellular, tissue, or organ level. Problems arise when the relation between the pathophysiology of the disease and the mechanism of action of the intervention is not properly understood; when adverse effects obviate therapeutic effects; when confounding factors, such as other drugs, alter the surrogate independently of the final end-point; when a biomarker persists after resolution of the disease; and when the concentration-effect curves for the effects of an intervention on the primary outcome and the surrogate are different. Use of biomarkers may also be hindered by poor reproducibility of measurement techniques. Challenges for clinical pharmacologists are to devise biomarker tests that are reliable, reproducible, sensitive, and specific, and surrogate end-points that are associated with the clinical outcomes of concern and useful. A robust taxonomy is needed of the relations that link the pathophysiology of disease, the mechanisms of action of interventions and their adverse effects, the desired clinical outcomes, and the surrogate end-points that predict them.

A review of the evidence concerning hepatic glutathione depletion and susceptibility to hepatotoxicity after paracetamol overdose

Paracetamol (acetaminophen) poisoning is common throughout the world. The management of nonstaggered (acute) paracetamol overdose is based on the plasma paracetamol concentration plotted on a treatment nomogram. In the UK there are two treatment lines on this nomogram, with the lower treatment line used for individuals felt to be at ‘high risk’ of paracetamol-related hepatotoxicity either as a result of induction of cytochrome P450 isoenzymes or reduction of intrahepatic glutathione. In this article we review the risk factors that, in current guidelines, are felt to increase risk due to a reduction in intrahepatic glutathione concentrations. Based on our review of the published literature, we feel that cystic fibrosis, acute viral illness, malnutrition, and eating disorders such as anorexia nervosa are likely to be associated with reduction in intrahepatic glutathione concentrations, and that this risk is likely to be related to malnutrition secondary to the disease. Chronic hepatitis C infection is also associated with reduced glutathione concentrations, although this appears to be independent of any associated malnutrition. Ageing and acute fasting are not associated with an increased risk of paracetamol-related hepatotoxicity due to reductions in glutathione concentrations. Finally, the evidence for HIV infection is inconclusive, particularly as the majority of studies were conducted in the pre-anti-viral treatment (HAART) era; however it is likely that patients with symptomatic HIV/AIDS have reduced glutathione concentrations due to associated malnutrition. Although there have been few studies which have specifically investigated whether there is an association between reduced intrahepatic glutathione concentrations and increased risk of paracetamol-related hepatotoxicity, in our opinion, it is likely that the above conditions that are associated with reduced glutathione concentrations, will be associated with an increased risk of paracetamol-related hepatotoxicity.

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.

An analysis of the length of hospital stay after acetaminophen overdose

BACKGROUND

Acetaminophen is one of the most commonly encountered medications in self-poisoning, with a high rate of morbidity. The prevalence and characteristics of acetaminophen intoxication associated with long hospital stay in patients are not well defined.

OBJECTIVES

This study aims to identify the clinical and demographic factors associated with the length of in-hospital stay (LOS), and to evaluate the effect of early treatment of acetaminophen overdose patients (≤8 hours) by intravenous N-acetylcysteine (IV-NAC) on hospital stay.

METHODS

This is a retrospective cohort study of hospital admissions for acetaminophen overdose conducted over a period of 5 years from 1 January 2004 to 31 December 2008. Patients were divided into two groups: LS group patients had a long hospital stay (> median hours stay in hospital) and SS group patients had a short hospital stay (≤ median hours stay in hospital). Variables were abstracted from medical records for comparison between the two groups. A total of 20 variables were identified for comparison. 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.

RESULTS

Of the 305 patients, 11 factors were identified in the univariate analysis as associated with LS. Three independent factors were found to be significant predictors of LS in the multivariate analysis. The factors associated with LS were seen among patients with a history of abdominal pain after ingestion of acetaminophen (p = 0.04), who were on IV-NAC administration (p < 0.001) and had an acutely depressed mood (p = 0.003). Late time to NAC infusion of more than 8 hours was associated with LS rather than SS (96 patients [57%] and 6 [24%], respectively; p = 0.003).

CONCLUSION

Patients with long hospital stay have different clinical characteristics compared to patients with short hospital stay. We identified time to IV-NAC administration is a potentially modifiable factor that may lead to prolonged hospital stay. When risk assessment indicates that NAC is required, it is highly recommended that NAC be started in the first hours of admission to reduce the LOS.

Toxicology today: what you need to know now

Clinicians are frequently confronted with toxicological emergencies and challenged with the task of correctly identifying the possible agents involved and providing appropriate treatments. In this review article, we describe the epidemiology of overdoses, provide a practical approach to the recognition and diagnosis of classic toxidromes, and discuss the initial management strategies that should be considered in all overdoses. In addition, we evaluate some of the most common agents involved in poisonings and present their respective treatments. Recognition of toxidromes with knowledge of indications for antidotes and their limitations for treating overdoses is crucial for the acute care of poisoned patients.

Hospital admission for non-fatal poisoning with weak analgesics and risk for subsequent suicide: a population study

BACKGROUND

Poisoning with weak analgesics is a major public health problem because of easy accessibility of the compounds; however, few studies have investigated their influence on subsequent suicide in the context of subjects' psychiatric status and other factors.

METHOD

This nested case-control study was based on the entire Danish population including all 21,169 suicide cases and 423,128 matched population controls. Data on hospital admissions for poisoning and confounding factors were retrieved from national medical and administrative registries. Conditional logistic regression was used to compute relative risk.

RESULTS

A prior hospital admission for poisoning with weak non-opioid analgesics significantly increased the risk of subsequent suicide [crude incidence rate ratio (IRR) 24.7, 95% confidence interval (CI) 22.1-27.6], and the effect of paracetamol poisoning was substantially stronger than that of poisoning with salicylates or non-steroidal anti-inflammatory drugs (NSAIDs). This association could not be explained by confounding from socio-economic or psychiatric factors. The elevated risk was extremely high during the first week following the overdose (adjusted IRR 738.9, 95% CI 173.9-3139.1), then declined over time but still remained significantly high 3 years later (adjusted IRR 4.2, 95% CI 3.5-5.0). Moreover, a history of weak analgesic poisoning significantly interacted with a person's psychiatric history, increasing the risk for subsequent suicide substantially more for persons with no history of psychiatric hospitalization than did it for those with such a history.

CONCLUSIONS

A history of non-fatal poisoning with weak analgesics is a strong predictor for subsequent suicide. These results emphasize the importance of intensive psychiatric care of patients following overdose.

Salivary paracetamol: evaluation of a colorimetric method in assessing deliberate self-poisoning

BACKGROUND

In the laboratory evaluation of suspected paracetamol poisoning, a non-invasive sample type that avoids venepuncture would be an attractive alternative to plasma, particularly in the paediatric setting. Salivary paracetamol measurement has not previously been evaluated in the published medical literature in the setting of deliberate self-poisoning (DSP).

METHODS

In-house validation experiments (recovery, stability and lower limit-of-detection) were performed on pooled saliva samples using a Roche Acetaminophen assay on a Roche/Hitachi 917 analyser. A clinical study of comparison of paired saliva and plasma samples was also conducted involving adult patients presenting with DSP of paracetamol, the results of which were published previously.

RESULTS

The validation experiments using pooled saliva samples showed: (i) mean recovery (paracetamol concentration 37.5-525 mg/L) 100.01% (+/-0.02 SD); (ii) precision of repeated assay over 24-h period CV <4%; (iii) lower limit-of-detection 0.9 mg/L. The clinical study of 21 patients with mean plasma paracetamol concentration of 48 mg/L (range 0-130) and mean saliva concentration 62 mg/L (range 0-183) showed good correlation between saliva and plasma concentrations (r(2) = 0.91).

CONCLUSIONS

The Roche Hitachi 917 Acetaminophen assay is suitable for the measurement of paracetamol in saliva. Further studies comparing plasma and saliva samples from patients with DSP and plasma paracetamol concentrations in the hepatotoxic range are warranted. If salivary samples are suitable for risk-stratifying patients with paracetamol DSP, venepuncture may be avoided, which would be attractive, especially in the paediatric setting.

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

INTRODUCTION

Despite extensive clinical experience, no dose-response curve exists for acetaminophen toxicity in man. The absence of accurate toxicodynamics has hampered efforts to optimize patient therapy and to identify risk modifiers following overdose. We set out to parameterize both the degree and duration of pretreatment exposure into a single, continuous measure of exposure, which will serve as the x-axis of an eventual dose-response curve.

METHODS

The model was constructed from pharmacokinetic first principles, using as inputs the vertical distance above the Rumack-Matthew nomogram line (expressed as the equivalent serum acetaminophen concentration 4 h after ingestion) and the delay to antidote therapy (tNAC). A no-effect dose ([APAP]threshold) and lag time (ti) were assumed.

RESULTS

The area under the serum acetaminophen concentration vs. time curve bounded by [APAP]threshold, ti and tNAC represents our proposed time-weighted measure of exposure. We demonstrate that this non-negative area estimates the cellular burden of toxic adducts formed following overdose. This measure is also easily calculated at patient presentation using clinical data and allows for both declining serum acetaminophen concentrations and variable delays to antidote therapy.

DISCUSSION

We describe a new, pharmacokinetically based measure of exposure following acute acetaminophen overdose treated with N-acetylcysteine. Using this measure should enhance the analysis of nonexperimental clinical data and permit more accurate characterization of acetaminophen toxicodynamics. Ultimately, this approach may facilitate progress on many of the long-standing controversies regarding acetaminophen toxicity in man.

alpha(1)-Adrenoceptor antagonists prevent paracetamol-induced hepatotoxicity in mice

BACKGROUND AND PURPOSE

Paracetamol, a major cause of acute liver failure (ALF) represents a significant clinical problem. Adrenoceptor stimulation or antagonism can modulate chemical-induced hepatotoxicity. We investigated the role of endogenous catecholamines and alpha(1)-adrenoceptors in the development of paracetamol- induced hepatotoxicity.

EXPERIMENTAL APPROACH

Paracetamol (3.5 mmol kg(-1)) was administered to male CD-1 mice, with and without alpha(1)-adrenoceptor antagonists (prazosin, doxazosin, terazosin and tamsulosin; 35.7 micromol kg(-1)). Serum transaminases and hepatic glutathione (GSH) levels were assessed as markers of hepatic damage. Paracetamol bioactivation was assessed by covalent binding, hepatic and urinary conjugate formation and uridine glucuronosyltransferase activity. Plasma catecholamines levels and hepatic congestion were also analysed.

KEY RESULTS

Plasma catecholamine levels were significantly elevated 5 h post paracetamol administration. Prazosin prevented hepatotoxicity when administered 1 h before a toxic paracetamol insult and importantly, when administered up to 1 h post paracetamol injection. Prazosin had no effect on paracetamol-induced depletion of hepatic GSH, paracetamol bioactivation or paracetamol-induced transcription of defence genes. Paracetamol toxicity is associated with marked accumulation of erythrocytes within hepatic sinusoids and prazosin completely prevented this accumulation.

CONCLUSION AND IMPLICATIONS

Paracetamol-induced hepatocellular damage is associated with increased circulating catecholamines. alpha(1)-Adrenoceptor antagonists conferred complete protection from paracetamol -induced hepatotoxicity. Protection was associated with absence of hepatic erythrocyte accumulation. Increased catecholamine levels may contribute to the pathophysiology of paracetamol-induced hepatotoxicity by compromising hepatic perfusion. Protection against paracetamol toxicity by alpha(1) antagonists in mice has implications for therapeutic management of patients presenting with paracetamol overdose and ALF.

Death from paracetamol overdose despite appropriate treatment with N-acetylcysteine

A case of death from severe paracetamol poisoning which presented early and received appropriate treatment according to evidence-based guidelines is presented here. It is very rare for patients to die from paracetamol poisoning when they receive N-acetylcysteine (NAC) within 8 h of ingestion. The patient had a marked lactic acidosis on presentation to hospital. This case demonstrates that a patient can die from paracetamol poisoning despite early and appropriate treatment, and raises the question whether lactic acidosis in a patient following paracetamol overdose should prompt the initiation of NAC treatment while awaiting paracetamol levels.

Update on the role of non-opioids for postoperative pain treatment

Non-opioids play an ever increasing role in the treatment of postoperative pain; either on their own for mild to moderate pain or in combination with other analgesic approaches, in particular opioids, as a component of multimodal analgesia. The analgesics paracetamol (acetaminophen) and dipyrone (metamizole) as well as compounds with an additional anti-inflammatory effect (non-selective non-steroidal anti-inflammatory drugs and selective cyclo-oxygenase-2 inhibitors) are used widely in the perioperative period. Paracetamol is gaining renewed interest in this setting due to its minimal adverse effects and recent availability in a parenteral preparation, but its benefits are insufficiently studied. Dipyrone continues to be used in many countries despite the ongoing debate on the incidence and relevance of its ability to cause agranulocytosis. Among the anti-inflammatory drugs, selective cyclo-oxygenase-2 inhibitors have the most supportive data for their beneficial effects as a component of multimodal analgesia and offer benefits with regard to their adverse effect profile.

Impact of Restricting Paracetamol Pack Sizes on Paracetamol Poisoning in the United Kingdom

Paracetamol (acetaminophen) is the most common drug taken in overdose in the UK, accounting for 48% of poisoning admissions to hospital and being involved in an estimated 100-200 deaths per year. In 1998, the UK government introduced legislation that reduced the maximum pack size of all non-effervescent tablets and capsules containing aspirin (acetylsalicylic acid) or paracetamol that can be sold or supplied from outlets other than registered pharmacies from 25 to 16 tablets or capsules. This article reviews the literature to determine the effectiveness of the legislation, focusing specifically on paracetamol poisoning. Seventeen studies on this subject were identified. Three studies found reductions in mortality rates; one study found an increase in mortality rates, while one found an initial reduction followed by an eventual increase; three found no significant difference in mortality rates before and after introduction of the legislation. Five studies found reductions in admissions to liver units, three of these finding a reduction in liver transplantation rates; two further studies found no change in liver function tests and rates of paracetamol-induced acute liver injury or failure. Four studies found a sustained decrease in hospital admissions, while two found an initial decrease followed by an eventual increase. One study found a decline in admissions for paracetamol poisoning and an increase in admissions for non-paracetamol poisoning. Sales data are conflicting, with two studies finding no significant difference in paracetamol sales before and after the introduction of the legislation and one reporting a decline. The severity of overdose appears to have decreased since the maximum permitted packet size was reduced, with five studies reporting a reduction in the number of severe overdoses (measured by numbers of tablets ingested, serum paracetamol concentrations and usage of antidotes). Only two studies reported an increase in the number of severe overdoses.Paracetamol-associated mortality rates, admissions to liver units/liver transplants, hospital admissions and the severity of paracetamol overdose appear to have been decreasing since 1998. However, one study showed that the reductions in mortality and hospital admissions began in 1997; therefore, the contribution of the 1998 legislation to the observed changes is unclear. Most of the studies are based on short-term follow-up so it is difficult to draw any conclusions regarding long-term trends. Many of the studies were also restricted to relatively small areas of the UK; this, combined with a variety of outcome measures, makes it difficult to distinguish any conclusive trends. The studies also suffer from a lack of comparison and control groups. Some studies do not clearly differentiate between the paracetamol preparations covered by the legislation and those not. The limited number of studies to date, combined with a variety of outcome measures, make it difficult to determine with accuracy whether or not the legislation has been a success. More long-term studies are needed to fully assess the impact of the legislation.

The hospital management of fatal self-poisoning in industrialized countries: an opportunity for suicide prevention?

Suicide by self-poisoning is a prevalent cause of death worldwide. A substantial proportion of individuals who poison themselves come into contact with medical services before they die. Our focus in the current study was the medical management of drug self-poisoning in industrialized countries and its possible contribution to suicide prevention. We reviewed the literature to determine the proportion of self-poisoning suicides who reach hospital alive, the sociodemographic and clinical characteristics of in-hospital overdose deaths, the in-hospital management this group of patients receives, and whether there are specific aspects of pre-hospital care and in-hospital management that have the potential to improve survival. Between 11% and 28% of individuals who died following deliberate ingestion of drugs reached hospital alive. The substances which were most frequently implicated in death were paracetamol (acetaminophen) and paracetamol compounds, tricyclic antidepressants, and benzodiazepines. Most patients received fairly intensive treatment, yet death may have been preventable in a small proportion of cases. Only one intervention (the administration of acetylcysteine) was shown to reduce mortality and this was in a highly selected group of patients (those who had ingested paracetamol and developed fulminant hepatic failure). It is possible that other interventions such as better airway management, the prompt administration of activated charcoal, and improved pre-hospital care may improve outcomes but their potential contribution to suicide prevention needs to be investigated in future studies.

Deliberate self-poisoning with acetaminophen: a comparison with other medications

BACKGROUND

Acetaminophen is the most common drug employed in deliberate self-poisoning (DSP) in many countries and can lead to acute liver failure. The purpose of the present study was to compare DSP with acetaminophen with DSP with other medications.

METHODS

From January 2001 to December 2002, all patients admitted after DSP to Soroka University Hospital in Beer-Sheva, Israel, were identified. Demographic data and medical history were obtained retrospectively.

RESULTS

There were 282 incidences of DSP in the study period. The mean age of 94 patients with an acetaminophen overdose was lower than that of patients who had attempted DSP with other medications (24.8 vs. 34.6 years, p<0.001). There was no gender or ethnic difference between the groups. Patients with DSP with acetaminophen were less likely to make recurrent attempts (23.4% vs. 39.9% p=0.006), less likely to have psychiatric disorders (32% vs. 59% p<0.001), and had a shorter hospital stay (1.7 vs. 2.1 days, p=0.05). The acetaminophen group had less of an impairment in level of consciousness (84% vs. 52.1% p<0.001) and had less need for ICU care (6.4% vs. 14.9%, p=0.04). Serum levels were checked in 68 (72.3%) of the patients in the acetaminophen group and they were found to be high in 6 (8.8%) of them (95% CI 2.1-15.5%).

CONCLUSION

Taking an overdose of acetaminophen is a common method of DSP, with patients tending to have a more benign presentation and shorter hospital stay than those who attempt DSP with other medications. Further research on the optimal care of these patients and multi-disciplinary approaches to DSP prevention are needed.

Paracetamol overdose and hepatotoxicity at a regional Australian hospital: a 4-year experience

BACKGROUND

Paracetamol is a component of a number of drugs taken in overdose (OD). The influence of alcohol use (acute or chronic) on the presentation and clinical course of paracetamol OD is contentious. This study explores the relationship between paracetamol OD, alcohol consumption and clinical outcomes at a regional Australian hospital.

AIMS

To determine the frequency, circumstances and outcomes of paracetamol OD presentations to a regional Australian general hospital over a 4-year period.

METHODS

Medical records of patients admitted to the Ballarat Health Services (BHS) as a result of paracetamol OD between January 2000 and December 2003 were reviewed. Patient demographics, amount of paracetamol ingested, other drug coingestions, alcohol history, previous medication OD, clinical course and outcomes were recorded.

RESULTS

Annual admissions resulting from paracetamol OD almost doubled during the 4 years studied. The risk of a repeat paracetamol OD was highest within 4 weeks of the initial OD. Alcohol, benzodiazepines and antidepressants were commonly coingested. The strongest predictor of severe hepatotoxicity was delayed or no N-acetyl cysteine treatment in patients consuming greater than 10 g of paracetamol or with toxic serum paracetamol levels. A history of alcohol consumption did not appear to worsen outcomes.

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.

The administration of N-acetylcysteine causes a decrease in prothrombin time in patients with paracetamol overdose but without evidence of liver impairment

OBJECTIVE

To explore the effect of intravenous N-acetylcysteine (NAC) on the prothrombin time (PT) in patients with paracetamol overdose and persistent normal liver profile.

MATERIALS AND METHODS

This retrospective case series study examined all admissions with a diagnosis of paracetamol poisoning in a tertiary hospital between 1989 and 2002. Patients were included if they had ever received NAC infusion, had no biochemical evidence of liver damage, and had more than two measurements of PT. Patients who had also ingested other drugs were excluded.

RESULTS

Of 65 admissions wtih paracetamol poisoning, 18 patients (10 men) met the inclusion criteria. The median age was 29 years, and the median quantity of paracetamol ingested was 186 mg/kg. The mean number of PT measurements per patient was 4.8. The baseline PT (as a percentage) 8.6 h after paracetamol ingestion was 89.6%. During NAC infusion the PT fell in all patients (range, 4.8-53.4% relative to baseline; P < 0.0001) at 14 h. The PT was less than 60% in 28% of the patients. Eight hours after the initiation of NAC there was a 16% fall in PT (range, 4.3-34%; P < 0.0001). At the end of NAC infusion all PTs returned to values close to baseline. Nine patients were hospitalized.

CONCLUSIONS

In patients with paracetamol overdose without evidence of liver damage a marked decrease in PT often occurs, which seems to be due to the overload of NAC infused at the beginning of treatment. This particular feature should be noted in clinical practice guidelines as a potentially misleading indicator of the development of severe liver dysfunction.

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.

[Paracetamol poisoning in infants aged less than six months: dosage errors]

In infants under 6 months of age, paracetamol overdose is usually due to dose confusion by caretakers. Recently, liquid formulations of this drug have been commercialized in larger,60-ml bottles. The syringe to measure the syrup in these new formulations is also bigger (5 cc versus 1.2-2 cc). We present six cases of 2-4-month-old infants mistakenly given an overdose of paracetamol, each from this new 60-ml formulation. These patients are especially susceptible to poisoning because of liver immaturity and require more aggressive management. To prevent this kind of poisoning, correct and clear information must be given to caregivers about drug dosage.

Management of paracetamol poisoning

Paracetamol is the most common substance involved in self-poisoning in the UK. The main advances made over the past five years in the management of early paracetamol poisoning, identification of risk factors for paracetamol poisoning, understanding of the mechanisms and management of late paracetamol poisoning and issues concerning the prevention of paracetamol poisoning are discussed.

Opioid and non-opioid analgesics

Opioids are the most potent analgesics. Toxicity results either from effects mediated by variation in affinity and intrinsic efficacy at specific opioid receptors or, rarely, from a direct toxic effect of the drugs. For some adverse effects, opioids exhibit a 'dual pharmacology' whereby these effects are usually observed only in pain-free individuals, and are not seen in patients in pain. Paracetamol, although generally very safe in therapeutic doses, displays potentially fatal toxicity in overdose requiring specific treatment. Non-steroidal anti-inflammatory drugs (NSAIDs) are known to act by inhibiting COX-1 and COX-2 isoenzymes to various degrees. Toxicity arises primarily from undesired inhibition at these enzyme sites. Knowledge of the mechanism of action of these drugs is fundamental to the understanding of their potential for toxicity, the details of which are still emerging.

Acetaminophen poisoning: an update for the intensivist

Acetaminophen overdose is common and can result from deliberate/nonstaggered or accidental/staggered ingestion. Patients presenting within 24 h of an acetaminophen overdose can safely be managed on medical wards. Early management of nonstaggered overdose is guided by the plasma acetaminophen concentration, whereas management of accidental/staggered ingestion is guided by ingested dose. Ingested dose and time from ingestion to presentation are important prognostic factors in accidental/staggered ingestion. Acetaminophen-induced acute liver failure (ALF) requires meticulous supportive care in an intensive care unit (ICU), with early identification and transfer of patients who are likely to require liver transplantation to a specialist liver centre. The modified King's College Hospital criteria (incorporating lactate into the traditional criteria) represent the best tool for identifying patients who require transplantation.