UMEM Educational Pearls - By Natasha Tobarran

Category: Toxicology

Title: Fomepizole for acetaminophen overdose?

Keywords: acetaminophen overdose, fomepizole, NAC (PubMed Search)

Posted: 7/19/2023 by Natasha Tobarran, DO (Emailed: 7/20/2023) (Updated: 5/29/2024)
Click here to contact Natasha Tobarran, DO

Acetaminophen (APAP) is the leading cause of acute liver failure worldwide. Standard treatment for APAP overdose is with N-acetylcysteine (NAC), which is highly effective if given within 8 hours of ingestion.  However, in delayed presenters or massive ingestions patients can still develop hepatotoxicity. Adjunctive therapies can be considered in these cases including augmented NAC dosing, renal replacement, and fomepizole.

A small amount of APAP is metabolized to N-acetyl-p-benzoquinone imine (NAPQI) by cytochrome 2E1. In therapeutic doses, the body is able to detoxify the NAPQI using glutathione. In overdose, glutathione stores get depleted and NAPQI can cause hepatotoxicity. Mitochondrial damage in APAP overdose is mediated by the c-Jun-N-terminal Kinase (JNK) pathway. 

NAC works to replenish glutathione stores and detoxify NAPQI. In large overdoses, increased dosing of NAC may be necessary. Fomepizole is typically used for its alcohol dehydrogenase inhibitor property to treat methanol and ethylene glycol poisoning. Fomepizole is also a cytochrome 2E1 and JNK inhibitor and can be used in APAP overdose to block the formation of NAPQI and mitigate mitochondrial damage.  Dialysis can be used to eliminate APAP from the body completely in massive overdoses or if significant acidosis or renal failure. 

This study is a case series of 14 patients treated for APAP overdose between 2017 – 2021 at a tertiary hospital

  • Patients treated with standard NAC therapy
  • They also received IV fompeizole loading dose of 15 mg/kg followed by 10mg/kg every 12 hours at the discretion of the treating team
  • Most cases received only the loading dose
  • Some cases also received renal replacement therapies
  • Patients had “better than expected outcomes” based on initial presentation, APAP levels, liver function tests, and expected clinical course
  • No unfavorable outcomes
  • No side effects

Limitations of the study:

  • Patients were treated with NAC which is the standard of care
  • No formal protocol for the administration or identification of patients treated with fompeizole

In summary:

  • NAC is the standard of care in acetaminophen poisonings
  • Consider fomepizole as an adjunctive therapy in patients that are critically ill
  • Consult your poison center 1-800-222-1222 or friendly toxicologist for help in identifying these patients

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Category: Toxicology

Title: Falsely Elevated Lithium Levels

Keywords: Lithium, Lab error, Toxicity (PubMed Search)

Posted: 6/15/2023 by Natasha Tobarran, DO (Updated: 5/29/2024)
Click here to contact Natasha Tobarran, DO

Lithium toxicity can present acutely with gastrointestinal symptoms and chronically with neurologic symptoms such as tremor and ataxia. Diagnosis and treatment with normal saline hydration and/or dialysis depends on lithium levels in conjunction with signs and symptoms.

Lithium levels can be falsely elevated when blood samples are collected in green top tubes which contain lithium heparin, or if the blood collection volume is too small.  Not recognizing that a lithium level may be falsely elevated can lead to misdiagnosis as well as unnecessary hospitalizations and treatments. The study by Wills et al found lithium levels as high as 4 mmol/L (therapeutic range 0.6-1.2 mmol/L) in lithium naïve volunteers collected in the wrong tube and with small blood volumes. If a patient has an elevated lithium level in the absence of lithium toxicity symptoms, consider a falsely elevated level and redraw using the appropriate tube and sample size. 

In summary:

  • Ensure the lithium sample is collected in a non heparin containing tube
  • Confirm sufficient sample volume
  • Look at the clinical picture when deciding on treatment for patient
  • Have a low threshold to repeat the lithium level
  • Consult your poison center 1-800-222-1222 or friendly toxicologist

Show References