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# Acetylcysteine ## Overview Acetylcysteine (NAC) is a mucolytic agent and an antidote for acetaminophen overdose. It is available in oral, intravenous, and inhalation formulations. ## Primary Indications * **Acetaminophen Overdose:** Intravenous (IV) is the preferred route for acute overdose to prevent hepatotoxicity. Oral may be used if IV access is not immediately available or for specific protocols. * **Mucolytic:** For conditions with thickened bronchial secretions (e.g., COPD, cystic fibrosis, pneumonia). Typically administered via nebulization. ## Adult Dosing * **Acetaminophen Overdose (IV):** * **Loading Dose:** 150 mg/kg IV infused over 1 hour. * **Second Dose:** 50 mg/kg IV infused over 20 hours (total infusion time 21 hours). * **Subsequent Doses:** 150 mg/kg IV infused over 20 hours. * *Note:* Dosing is often guided by nomograms and hospital protocols, especially for late presentations or elevated AST/ALT. Higher doses may be used in severe cases. * **Acetaminophen Overdose (Oral):** * **Loading Dose:** 140 mg/kg PO. * **Subsequent Doses:** 70 mg/kg PO every 4 hours for 17 doses (total 71 hours). * *Note:* Oral NAC is less effective than IV due to lower bioavailability and potential for emesis. Antiemetics are often required. * **Mucolytic (Nebulization):** * 3-5 mL of 20% solution or 6-10 mL of 10% solution, nebulized every 4-12 hours as needed. ## Pediatric Dosing * **Acetaminophen Overdose (IV):** * Same as adult dosing: 150 mg/kg IV over 1 hour, followed by 50 mg/kg IV over 20 hours, then 100 mg/kg IV over 16 hours (adapted from adult protocol for a total of 21 hours). * *Note:* Protocols for pediatric IV NAC dosing can vary; confirm with local guidelines. * **Acetaminophen Overdose (Oral):** * Same as adult dosing: 140 mg/kg PO, followed by 70 mg/kg PO every 4 hours for 17 doses. * **Mucolytic (Nebulization):** * **<1 year:** 2 mL of 10% solution or 1 mL of 20% solution every 2-6 hours. * **1-2 years:** 2-4 mL of 10% solution or 1-2 mL of 20% solution every 2-6 hours. * **>2 years:** 3-5 mL of 20% solution or 6-10 mL of 10% solution every 2-6 hours. ## Dose Adjustments * **Hepatic Impairment:** No specific dose adjustment is typically recommended for acetaminophen overdose due to the goal of preventing further injury. * **Renal Impairment:** No specific dose adjustment is typically recommended for acetaminophen overdose. For mucolytic use, monitor for efficacy. ## Contraindications * Hypersensitivity to acetylcysteine. * Oral formulation is contraindicated in patients with a suspected or confirmed esophageal obstruction. ## Adverse Effects * **IV:** Anaphylactoid reactions (rash, urticaria, angioedema, bronchospasm, dyspnea, hypotension) are common and can occur even after repeated administrations. Nausea, vomiting, and flushing can also occur. * **Oral:** Nausea, vomiting, diarrhea, stomatitis. * **Nebulization:** Bronchospasm, nausea, vomiting, stomatitis, rhinorrhea. ## Key Drug Interactions * **Activated Charcoal:** Decreases absorption of oral acetylcysteine. Administer NAC at least 1 hour after charcoal. * **Nitroglycerin:** May potentiate the hypotensive effect of nitroglycerin. ## Monitoring * **Acetaminophen Overdose:** * Acetaminophen and its toxic metabolite (NAPQI) levels. * Liver function tests (AST, ALT, bilirubin, INR). * Renal function and electrolytes. * Clinical signs of liver injury. * **Mucolytic Use:** * Respiratory status, sputum production, and airway patency. * Bronchospasm (especially in asthmatics). ## Clinical Pearls * For acetaminophen overdose, initiate NAC as soon as possible, even if the acetaminophen level is not yet available or if the time of ingestion is uncertain. * Anaphylactoid reactions to IV NAC are common and typically managed with slowing the infusion rate and administering antihistamines. Discontinuation is usually not necessary unless severe. * Ensure adequate hydration when administering oral NAC to prevent dehydration and facilitate passage. * Consider acetylcysteine for indications other than acetaminophen overdose, such as contrast-induced nephropathy (though evidence is mixed and not a standard indication) or as an adjunct in some pulmonary conditions. *** *This information is intended for healthcare professionals. It is essential to consult the most current prescribing information and relevant clinical guidelines before making any treatment decisions.*