[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Specific antidotes](https://durgical.com/en/pharmacology/classes/specific-antidotes/) › Acetylcysteine [Pharmacology](https://durgical.com/en/pharmacology/) · [Specific antidotes](https://durgical.com/en/pharmacology/classes/specific-antidotes/) # Acetylcysteine The antidote for paracetamol (acetaminophen) overdose: it refills the liver's glutathione so the toxic metabolite is neutralised before it kills liver cells. Updated 2026-11-01 - Class: [Specific antidotes](https://durgical.com/en/pharmacology/classes/specific-antidotes/) - Target: Hepatic glutathione and the toxic metabolite NAPQI - ATC code: V03AB23 - WHO Model List of Essential Medicines Also called: N-acetylcysteine (NAC) ## Mechanism of action In overdose, the liver's conjugation pathways saturate and more paracetamol goes through cytochrome P450 to NAPQI, a reactive metabolite normally neutralised by glutathione. When glutathione runs out, NAPQI binds liver proteins and causes centrilobular necrosis. Acetylcysteine is a cysteine donor that restores glutathione, and it can also act as a substitute for glutathione in conjugating NAPQI. It protects best when started early after the ingestion. - Overdose: more paracetamol becomes toxic NAPQI - Glutathione runs out and NAPQI damages liver cells - Acetylcysteine refills glutathione and binds NAPQI - Less liver necrosis, best if started early ## Pharmacokinetics **Distribution** Moderate volume of distribution; largely bound to plasma proteins **Metabolism** Converted to cysteine and other metabolites, feeding glutathione synthesis **Elimination** The kidneys account for roughly a third of its clearance **Half-life** About five and a half hours after intravenous use **Onset and duration** Maximal liver protection when started within about 8 hours of an acute ingestion; it is still given later ## Indications - Paracetamol (acetaminophen) overdose, guided by the time of ingestion and the serum level on the treatment nomogram [Acetaminophen toxicity →](https://durgical.com/en/conditions/acetaminophen-toxicity/) - Repeated supratherapeutic paracetamol use with raised levels or liver enzymes (the nomogram does not apply) [Acetaminophen toxicity →](https://durgical.com/en/conditions/acetaminophen-toxicity/) ## Adverse effects ### Common - Flushing, urticaria and itching, mostly early in the infusion - Nausea and vomiting - Tachycardia and oedema ### Serious (rare, important) - Anaphylactoid reactions with bronchospasm and hypotension; faster infusion raises the risk - Fluid overload with hyponatraemia and seizures, especially in small children ## Contraindications - Previous hypersensitivity reaction to acetylcysteine (relative: in a serious overdose the benefit is weighed against the risk) ## Key interactions **Nitroglycerin** Acetylcysteine may increase its hypotensive effect **Activated charcoal (oral acetylcysteine)** Both are given in early poisoning; the oral antidote and the charcoal are spaced so the charcoal does not adsorb it ## What is monitored - Serum paracetamol level at the right time after ingestion - ALT/AST and INR, at the start and after the last bag - Signs of allergic reaction during the first infusion - Sodium and fluid balance in children and in fluid-restricted patients ## Administration and safety - The intravenous solution is hyperosmolar and must be diluted before use - Given as a sequence of infusions; volumes are reduced for small children and fluid-restricted patients - If an allergic reaction occurs, the infusion is stopped, the reaction treated, and the infusion may be restarted carefully - Treatment is not withheld while waiting for a level when the patient arrives late or the time of ingestion is unknown ## Nursing care - Record the time of ingestion and the amount reported - Watch skin, breathing and blood pressure closely in the first hour of infusion - Check the sequence and timing of each infusion bag - Track liver tests and INR when the course ends - Ask about suicidal intent and arrange mental-health assessment ## Pregnancy and breastfeeding Data in pregnancy are limited, but delaying treatment of a paracetamol overdose raises maternal and fetal risk, so it is used in pregnancy. ## Memory aid NAC = Need A Cysteine: paracetamol eats the liver's glutathione, NAC refills it, and the clock (8 hours) decides how much it saves. ## Test yourself Think of the answer, then tap the question to see it. ## Which metabolite of paracetamol damages the liver in overdose? NAPQI, formed by cytochrome P450 when conjugation is saturated; glutathione normally neutralises it. ## How does acetylcysteine protect the liver? It donates cysteine to rebuild glutathione and can conjugate NAPQI itself. ## Why is acetylcysteine started even when the patient arrives late? Protection is greatest within about 8 hours but some benefit remains, it does not worsen the patient, and the reported time may be wrong. ## What is the most common serious reaction during the first infusion? An anaphylactoid reaction (flushing, urticaria, bronchospasm, hypotension); it is managed and the infusion can often be restarted. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/acetylcysteine/) ## Related drugs - [Activated charcoal](https://durgical.com/en/pharmacology/activated-charcoal/) ## Related conditions - [Acetaminophen toxicity](https://durgical.com/en/conditions/acetaminophen-toxicity/) [← Back to the class: Specific antidotes](https://durgical.com/en/pharmacology/classes/specific-antidotes/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [DailyMed - ACETYLCYSTEINE injection, solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=f811ddfc-d7c1-4637-ae81-80c38a77cb80) (DailyMed (U.S. National Library of Medicine), 2026); [Guía para el Manejo de Emergencias Toxicológicas](https://minsalud.gov.co/sites/rid/Lists/BibliotecaDigital/RIDE/DE/GT/guias-manejo-emergencias-toxicologicas-outpout.pdf) (Ministerio de Salud y Protección Social; Organización Panamericana de la Salud, 2017); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=V03AB23) (WHO Collaborating Centre for Drug Statistics Methodology, 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/acetylcysteine/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/acetylcysteine/