# A patient arrives at the emergency department after ingesting an unknown amount of acetaminophen 4 hours ago. The patient is conscious but reports nausea and vomiting. Laboratory results show elevated liver enzymes. Which antidote should the nurse prepare to administer? > source: MyMerci (mymerci.kr) > url: https://mymerci.kr/pages/nclex_q.php?qn_id=540352 > language: ko > subject: Adult Health ## 문제 A patient arrives at the emergency department after ingesting an unknown amount of acetaminophen 4 hours ago. The patient is conscious but reports nausea and vomiting. Laboratory results show elevated liver enzymes. Which antidote should the nurse prepare to administer? ## 보기 1. N-acetylcysteine **✔ 정답** 2. Flumazenil 3. Naloxone 4. Activated charcoal **정답: 1** ## 해설 N-acetylcysteine is the specific antidote for acetaminophen overdose and should be administered within 8-10 hours of ingestion for maximum effectiveness. Acetaminophen overdose is a serious medical emergency requiring immediate treatment. Pathophysiologically, it depletes glutathione stores in the liver, leading to accumulation of toxic metabolites and causing liver cell damage. N-acetylcysteine (NAC) is the specific antidote for acetaminophen poisoning, replenishing glutathione stores and providing an alternative pathway for detoxification. It is most effective when given within 8-10 hours of ingestion, though it can still be effective up to 24 hours. The typical protocol includes a loading dose followed by a maintenance infusion. In this scenario, the patient shows initial toxic signs (nausea, vomiting) and laboratory evidence of liver injury (elevated liver enzymes) 4 hours after ingestion. This point is a critical window where NAC administration can prevent or minimize liver damage. The nurse should prepare for immediate administration while monitoring for potential adverse effects such as anaphylactoid reactions. Early recognition and prompt treatment with NAC can significantly improve patient outcomes and prevent progression to fulminant hepatic failure, which may require liver transplantation. Flumazenil is a benzodiazepine antidote, naloxone is an opioid antidote, and activated charcoal reduces absorption but has limited effectiveness after 4 hours. ## 심화 해설 Clinical Context and Pathophysiology The patient’s presentation—ingestion of an unknown amount of acetaminophen approximately 4 hours prior, accompanied by nausea and vomiting—is a classic early manifestation of acetaminophen toxicity. Acetaminophen is responsible for more pharmaceutical overdoses than any other medication in the United States and is the leading cause of acute liver failure [3]. In therapeutic doses, acetaminophen is primarily metabolized via glucuronidation and sulfation. However, in overdose, these pathways become saturated, shunting metabolism toward the cytochrome P450 system, which produces the highly reactive and hepatotoxic metabolite N-acetyl-p-benzoquinone imine (NAPQI). NAPQI is normally detoxified by conjugation with hepatic glutathione, but once glutathione stores are depleted, NAPQI binds to hepatocellular proteins, causing centrilobular necrosis and potentially severe acute liver failure [1]. Antidote Mechanism and Rationale The correct antidote is N-acetylcysteine (NAC). Introduced as an antidote in 1974, NAC has revolutionized the management of acetaminophen poisoning by significantly reducing hepatotoxicity and associated mortality [1]. NAC works through multiple mechanisms: it serves as a glutathione precursor, replenishing depleted hepatic glutathione stores to detoxify NAPQI; it directly conjugates with NAPQI; and it may have antioxidant and hemodynamic effects. The standard treatment involves a three-bag intravenous protocol, though recent research has explored abbreviated 12-hour infusions compared to the traditional 20-hour regimen [4]. While NAC is widely considered safe when administered appropriately, the nurse must be vigilant, as improper administration—such as iatrogenic overdose—has been associated with serious adverse outcomes including cerebral edema and hemolytic uremic syndrome [2]. Analysis of Incorrect Options - Flumazenil is a benzodiazepine receptor antagonist used to reverse benzodiazepine overdose. It has no role in acetaminophen toxicity and could precipitate seizures in patients with unknown co-ingestions. - Naloxone is an opioid receptor antagonist indicated for opioid overdose. While many combination products contain both acetaminophen and opioids, naloxone does not address the hepatotoxic threat of acetaminophen itself [3]. - Activated charcoal may be considered for gastrointestinal decontamination if the patient presents within 1 to 2 hours of ingestion. At 4 hours post-ingestion, its benefit is significantly diminished, and it is not an antidote for the systemic toxicity that has already begun. NAC remains the priority intervention. Nursing Considerations and Clinical Judgment The nurse should anticipate preparing NAC for intravenous administration based on the patient’s weight and the institution’s protocol. Given the patient’s persistent nausea and vomiting, the nurse must recognize that antiemetic administration may be necessary to facilitate NAC tolerance, as vomiting is a common side effect of both the toxicity and the antidote infusion. The nurse should also prepare to draw a serum acetaminophen level, liver function tests, and coagulation studies to plot on the Rumack-Matthew nomogram, which guides the necessity and duration of NAC therapy. The presence of acetaminophen protein adducts in circulation serves as a highly sensitive biomarker of oxidation and potential hepatic injury, confirming the need for continued monitoring even after antidote completion [4].References (research sources) - [1][Translated article] N-acetylcysteine: 50 years since the discovery of an antidote that has changed the prognosis of acetaminophen poisoning.Research articleNogué-Xarau S, Martínez-Sánchez L, García-Peláez M, Fernández de Gamarra-Martínez E, Pi-Sala N, Gispert-Ametller À, Salgado-García E, Aguilar-Salmerón R. (2026) · DOI: 10.1016/j.farma.2025.10.015 - [2]Safety of acetylcysteine: a scoping review of iatrogenic overdose cases and their associated complications.Research articleBaker MB, Young J, Binda DD, Dienes E, Kennedy JM. (2026) · DOI: 10.1080/15563650.2026.2673132 - [3]Acetaminophen ToxicityResearch articleSchaffer DH, Murray BP, Khazaeni B. (2026) - [4]Paracetamol adducts following overdose treated with a shorter acetylcysteine infusion: findings from the NACSTOP 2 trial.Research articleWong A, James LP, McNulty R, Gunja N, Graudins A. (2026) · DOI: 10.1080/15563650.2026.2655388 ## 임상 시나리오 Clinical Management of Acute Acetaminophen Overdose Effective management of acetaminophen poisoning hinges on rapid risk stratification and timely administration of the antidote, N-acetylcysteine (NAC), to prevent irreversible hepatic injury. 1. Initial Assessment and Risk Stratification - **Time of Ingestion:** Determine the precise time of ingestion if possible. The Rumack-Matthew nomogram is used for single, acute ingestions with a known time and a serum acetaminophen level drawn between 4 and 24 hours post-ingestion. - **Serum Acetaminophen Level:** Draw a stat level at 4 hours post-ingestion or as soon as possible thereafter. Plot the level on the nomogram to determine the need for NAC therapy. - **Baseline Labs:** Obtain liver function tests (ALT, AST, bilirubin, INR/PT), renal function (BUN, creatinine), and serum electrolytes. Elevated transaminases are a marker of evolving hepatotoxicity. 2. Antidote Administration: N-Acetylcysteine (NAC) - **Indication:** Initiate NAC immediately if the serum level is above the "possible risk" line on the nomogram, if the patient presents with hepatotoxicity regardless of the level, or if the ingestion is staggered/chronic with evidence of liver injury. - **Therapeutic Window:** NAC is most effective when given within 8 hours of ingestion, but it provides benefit even in late-presenting patients with established hepatic failure by supporting mitochondrial function and hemodynamics. - **Routes of Administration:** - **IV Protocol (21-hour):** A three-bag regimen is standard. A loading dose of 150 mg/kg in 200 mL of D5W over 1 hour, followed by 50 mg/kg in 500 mL over 4 hours, and then 100 mg/kg in 1000 mL over 16 hours. - **Oral Protocol (72-hour):** A loading dose of 140 mg/kg, followed by 70 mg/kg every 4 hours for 17 additional doses. This may be used if IV NAC is not available or for non-severe cases, though IV is preferred due to nausea and vomiting. - **Anaphylactoid Reactions:** Non-IgE mediated reactions (flushing, urticaria, bronchospasm) can occur with IV NAC, especially during the loading dose. Management involves pausing the infusion, administering antihistamines, and restarting at a slower rate once symptoms resolve. 3. Supportive Care and Monitoring - **GI Decontamination:** Activated charcoal (1 g/kg) can be considered if the patient presents within 1-2 hours of a massive ingestion, but it is not a substitute for NAC and is often avoided due to the high likelihood of vomiting. - **Hepatic Monitoring:** Repeat liver enzymes and coagulation studies every 12-24 hours. A rising INR or signs of encephalopathy indicate progression toward acute liver failure. - **Criteria for Transplant Referral:** If the patient develops indicators of poor prognosis (e.g., pH < 7.3, INR > 3.0, creatinine > 3.4 mg/dL, or grade III/IV encephalopathy), immediate consultation with a liver transplant center is mandatory. Nursing Considerations - Administer antiemetics as prescribed to manage nausea and vomiting, which can complicate oral NAC therapy. - Monitor for signs of fluid overload, especially in patients with renal compromise receiving large-volume IV NAC infusions. - Provide psychosocial support and assess for intentional self-harm, ensuring continuous one-to-one observation if indicated. ## 핵심 개념 - **N-acetylcysteine (NAC)** — The specific antidote for acetaminophen overdose that acts as a glutathione precursor to neutralize the toxic metabolite NAPQI and prevent hepatic necrosis. - **NAPQI (N-acetyl-p-benzoquinone imine)** — A highly reactive and hepatotoxic intermediate metabolite of acetaminophen produced via the CYP2E1 pathway, which causes cellular damage when glutathione stores are depleted. - **Glutathione** — A critical endogenous antioxidant in the liver responsible for conjugating and detoxifying NAPQI; its depletion in overdose leads to hepatotoxicity. - **Hepatotoxicity** — Chemical-driven liver damage, often presenting with nausea, vomiting, and elevated liver enzymes, as seen in acetaminophen poisoning. - **Rumack-Matthew Nomogram** — A tool used to assess the risk of hepatotoxicity after a single acute acetaminophen ingestion based on serum drug levels drawn 4 to 24 hours post-ingestion. ## 같은 주제 문제 - [A patient arrives at the emergency department after ingesting an unknown amount of acetami…](https://mymerci.kr/pages/nclex_q.php?qn_id=540353) - [A patient presents to the emergency department with suspected organophosphate poisoning fr…](https://mymerci.kr/pages/nclex_q.php?qn_id=540354) - [A patient arrives at the emergency department after ingesting an unknown amount of acetami…](https://mymerci.kr/pages/nclex_q.php?qn_id=540355) - [A nurse is caring for a patient who has just received naloxone for the reversal of a suspe…](https://mymerci.kr/pages/nclex_q.php?qn_id=540356) - [The nurse is monitoring a patient following naloxone administration for opioid overdose re…](https://mymerci.kr/pages/nclex_q.php?qn_id=540357) - [A nurse is caring for a patient who received an overdose of warfarin and is experiencing s…](https://mymerci.kr/pages/nclex_q.php?qn_id=540358) - [The nurse should monitor the patient most closely for which potential complication followi…](https://mymerci.kr/pages/nclex_q.php?qn_id=540359) - [A nurse is caring for a patient who accidentally ingested a large amount of acetaminophen …](https://mymerci.kr/pages/nclex_q.php?qn_id=540360) --- More free questions: [기출문제](https://mymerci.kr/) _학습 참고용입니다. 실제 임상은 최신 지침과 소속 기관 프로토콜을 따르세요._