Reduced toxicity of acetaminophen in children: it's the liver

Interventional cohort study of prolonged use (>72 hours) of paracetamol in neonates: protocol of the PARASHUTE study

INTRODUCTION

Anticipated or actual pain in neonates results in use of paracetamol for prolonged pain relief in many neonatal intensive care units. Clinical trials examining safety of paracetamol exposure in neonates have been of short duration (1-3 days) and hepatic biomarkers and paracetamol metabolism are rarely reported in the same studies.We aim to investigate the safety (hepatic tolerance) and effectiveness of prolonged paracetamol exposure in neonates by measuring hepatic biomarkers, plasma concentrations of paracetamol and its metabolites and pain scores. In addition, we study a possible interaction between ethanol and paracetamol.

METHODS AND ANALYSIS

A multicentre interventional cohort study.Neonates of any gestational age and up to 44 weeks postmenstrual age, treated with oral or intravenous paracetamol can be included.Alanine aminotransferase (ALT) and bilirubin are measured at baseline or within 24 hours after treatment initiation. P-paracetamol and metabolites are measured at steady state and every 2 days (opportunistically) together with ALT and bilirubin and lastly after discontinuation of treatment. COMFORT neo pain scores are collected longitudinally. COMFORT neo pain scores and population pharmacokinetic analysis of paracetamol samples will be analysed simultaneously using non-linear mixed effects models. One and two compartment models with first-order elimination will be tested for disposition. In addition, plasma ethanol is measured if the patient receives concomitant treatment with intravenous or oral phenobarbital containing ethanol as an excipient.

ETHICS AND DISSEMINATION

Inclusion of patients can be postponed 24 hours after the first paracetamol dose. This is intended to make the inclusion process less stressful for parents. This study uses standard dosing strategies. The potential risks are additional blood samples, which are collected opportunistically to reduce additional heel pricks.

TRIAL REGISTRATIONNUMBER

Ethics Comittee: H-17027244, EudraCT no: 2017-002724-25, BFH-2017-106, 05952.

Nephrotoxicity Associated with Acute Paracetamol Overdose: A Case Report and Review of the Literature

A 29-year-old, 65 kg, Chinese man presented to hospital 10 hours after ingesting 30 g of paracetamol (462 mg/kg body weight). The blood paracetamol level was 145 µg/ml at 10 hours post-ingestion. He had no known risk factors for hepatotoxicity and was treated with intravenous N-acetylcysteine (NAC). Serum creatinine level rose to a maximum of 455 µmol/L on day 8; it gradually declined without the need for dialysis. Little is known of the risk factors for nephrotoxicity, which may occur with or without concurrent liver damage, suggesting possible primary toxic effects on the kidney. The use of NAC in this case may have prevented the progression to liver failure and reduced the severity of the nephrotoxic effects.

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.

Are some people at increased risk of paracetamol-induced liver injury? A critical review of the literature

Purpose

Paracetamol is one of the world’s most commonly used drugs. In overdose, it is well established to be hepatotoxic. The aim of this review was to identify factors that have been, or actually are, associated with the development of liver injury after paracetamol exposure in humans.

Method

Google Scholar and PubMed were searched on various dates between December 2016 and March 2017. Papers identified had their references analysed for further studies that might be relevant.

Results

At the time of writing, there was little good quality clinical evidence—from studies of paracetamol overdose or therapeutic use—to suggest that any groups of people are relatively protected from, or are at greater risk of, liver injury. The factors that were historically used to indicate higher risk in the UK have no good quality clinical evidence to support their re-introduction into clinical practice. The safe (and still effective) oral dose of paracetamol in patients weighing less than 50 kg has not been established.

Conclusion

There is no patient group that is unequivocally at elevated risk of paracetamol-induced liver toxicity. We propose two clinical scenarios that warrant further research. Firstly, there is a need to establish whether the dose of paracetamol should be reduced in patients with low body weight. Secondly, if or when genomic information regarding individual patients becomes readily available to inform prescribing, we propose the contribution of the genome to paracetamol toxicity should be re-investigated with robustly designed studies. Such studies could enhance the safe use of one of the most frequently taken drugs.

Electronic supplementary material

The online version of this article (10.1007/s00228-017-2356-6) contains supplementary material, which is available to authorized users.

Paracetamol as a toxic substance for children: aspects of legislation in selected countries

Paracetamol is used widely in pediatrics because it has a high drug safety when used in therapeutic dosages. In case of overdose the majority of paracetamol is metabolized to N-acetyl-p-benzoquinone imine (NAPQI), which is responsible for the severe toxic effects. The covalent connection between NAPQI and hepatic proteins leads to hepatocellular damage and possibly to severe liver failure. The antidote for paracetamol is N-acetylcysteine (NAC). It is a precursor of glutathione and aids to fill glutathione stores. The Rumack-Matthew nomogram should be used to decide on antidote treatment. Pediatric drug metabolism differs from adult metabolism. Children have a larger liver size compared to their body weight than adults, resulting in a higher metabolism rate. Young children seem to be less sensitive to acute intoxication than adults. One hypothesis to explain the lower rate refers to the larger liver size. The acute toxic dosage for children is more than 200 mg/kg body weight. There seems to be a global increase in accidental pediatric paracetamol overdose. Governmental websites of various European Union (EU) countries were searched for legal information on paracetamol availability in pharmacies and non-pharmacy stores. Various EU countries permit prescription-free sales of paracetamol in pharmacies and non-pharmacy stores. In Sweden paracetamol 500 mg may be sold in both pharmacies and non-pharmacies in a maximum pack size of 20 units. In the United Kingdom (UK) paracetamol 500 mg is listed in the general sales list with a maximum pack size of 30 effervescent tablets or 16 tablets. In Ireland paracetamol 500 mg may be sold in a maximum pack size of 12 units in a non-pharmacy. In the Netherlands paracetamol 500 mg is legal to be sold in a maximum pack size of 50 units in a drug store and with a maximum of 20 units in any other non-pharmacy. Several countries in the European Union are permitted to offer paracetamol prescription-free in pharmacies and non-pharmacy stores without legal guidance on the storage position within the store. Further research is needed to investigate whether paracetamol is located directly accessible to young children within the stores in EU countries which permit prescription-free sales of paracetamol.

Four-hour acetaminophen concentration estimation after ingested dose based on pharmacokinetic models

INTRODUCTION

The United Kingdom has recently changed the indications for N-acetylcysteine treatment for acetaminophen intoxication. Any ingestion over 75 mg/kg is now referred to the hospital. A model based on pharmacokinetic parameters was developed to predict 4-h acetaminophen concentration for this and other ingested doses.

METHODOLOGY

EMBASE and Medline were searched to obtain values for volume of distribution, absorption, and elimination constants and bioavailability for acetaminophen. Four-hour concentrations were calculated for ingestion doses currently recommended for hospital referral in different countries. Calculated plasma concentrations at 4 h for several doses were plotted against the Rumack-Matthew and the United Kingdom treatment lines.

RESULTS

Six articles were used for the calculations (4 adult and 2 pediatric). In order to achieve a 4-h acetaminophen concentration of 100 mg/L, doses (mg/kg ± 99.9CI) of 180.5 ± 43.2 for adults and 396.1 ± 115.5 for children were calculated.

DISCUSSION

A dose of 75 mg/kg would likely yield a 4-h acetaminophen concentrations well below 100 mg/L. Medical toxicologists and poison information specialists are left without evidence-based guidance for which patients or which ingestion history would now warrant referral to hospital for acetaminophen concentration measurement. Larger toxicokinetic studies in acetaminophen overdose are needed to define ingestion dose for referral to hospital.

Effect of excipients on acetaminophen metabolism and its implications for prevention of liver injury

Acetaminophen poisoning is the most frequent cause of acute hepatic failure in the US. Toxicity requires reductive metabolism of acetaminophen, primarily via CYP2E1. Liquid acetaminophen preparations contain propylene glycol, a common excipient that has been shown to reduce hepatocellular injury in vitro and in rodents. Children are less susceptible to acetaminophen toxicity for unclear reasons. We conducted a pharmacokinetic single-blinded crossover study of 15 healthy adult volunteers comparing the CYP2E1 and conjugative metabolism of a 15 mg/kg dose of liquid versus solid preparations of acetaminophen. Measured AUC's for the CYP2E1 metabolites were 16-17% lower and extrapolated AUC's were 25-28% lower in the liquid formulation arm while there was no difference in conjugative metabolite production. The formation rate constants for reductive metabolites were equivalent between solid and liquid formulations indicating that enzyme inhibition was competitive. Propylene glycol, an established CYP2E1 competitive antagonist, was detected in the liquid formulation but not solid formulation arm. Since children tend to ingest liquid preparations, the protective effect of this excipient could explain their decreased susceptibility to acetaminophen toxicity. A less hepatotoxic formulation of acetaminophen could potentially be developed if co-formulated with a CYP2E1 inhibitor.