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# Acetylcysteine ## Overview N-acetylcysteine (NAC) is an mucolytic agent that breaks disulfide bonds in mucus, decreasing its viscosity. It is also an antidote for acetaminophen overdose. ## Primary Indications * **Acetaminophen Overdose:** Antidote to prevent or treat acetaminophen-induced hepatotoxicity. * **Mucolytic:** To thin mucus in respiratory conditions (e.g., cystic fibrosis, COPD, pneumonia, bronchitis). ## Adult Dosing ### Acetaminophen Overdose: * **Oral:** 140 mg/kg loading dose, followed by 70 mg/kg every 4 hours for 17 doses. * **Intravenous (IV):** Typically administered as a 3-bag protocol. * Bag 1: 150 mg/kg in 200 mL of 5% dextrose in water (D5W) infused over 60 minutes. * Bag 2: 50 mg/kg in 500 mL of D5W infused over the next 4 hours. * Bag 3: 100 mg/kg in 500 mL of D5W infused over the next 16 hours. * Total duration: 21 hours. Alternative IV protocols exist and may be preferred based on local guidelines. Maximum doses are generally not specified for the treatment of overdose but depend on the total amount of acetaminophen ingested. ### Mucolytic: * **Oral:** 200 mg to 400 mg two to three times daily. * **Nebulized:** 3 mL to 5 mL of a 20% solution (600-1000 mg) or 6 mL to 10 mL of a 10% solution (600-1000 mg) every 2 to 6 hours. * **Intravenous (IV):** Primarily used for acetaminophen overdose. Not typically used as a mucolytic via IV route. * **Direct Instillation (Bronchial):** 1 to 2 mL of a 20% solution every 1 to 4 hours. ## Pediatric Dosing ### Acetaminophen Overdose: * **Oral:** 140 mg/kg loading dose, followed by 70 mg/kg every 4 hours for 17 doses. * **Intravenous (IV):** Dosing is weight-based and follows the same 3-bag protocol as adults, adjusted for pediatric weight. For example: * Bag 1: 150 mg/kg in an appropriate volume of D5W (volume depends on patient weight, typically 3 mL/kg to max 200 mL) infused over 60 minutes. * Bag 2: 50 mg/kg in an appropriate volume of D5W (typically 7 mL/kg to max 500 mL) infused over the next 4 hours. * Bag 3: 100 mg/kg in an appropriate volume of D5W (typically 15 mL/kg to max 500 mL) infused over the next 16 hours. * Total duration: 21 hours. ### Mucolytic: * **Nebulized:** * **3 months to 3 years:** 1 mL to 2 mL of a 20% solution (200-400 mg) or 2 mL to 4 mL of a 10% solution (200-400 mg) every 2 to 6 hours. * **4 years to 12 years:** 3 mL to 5 mL of a 20% solution (600-1000 mg) or 6 mL to 10 mL of a 10% solution (600-1000 mg) every 2 to 6 hours. * **>12 years:** Same as adult nebulized dosing. ## Dose Adjustments * **Renal Impairment:** No specific dose adjustment is universally recommended for mucolytic use. For acetaminophen overdose, cautious use and close monitoring are advised; some sources suggest a potential need for adjustment, but clear guidelines are lacking. * **Hepatic Impairment:** No specific dose adjustment is recommended for mucolytic use. For acetaminophen overdose, hepatic function is impaired, necessitating close monitoring. ## Contraindications * Known hypersensitivity to acetylcysteine. * Active gastrointestinal bleeding (for oral formulation due to potential emesis). ## Adverse Effects * **Common:** Nausea, vomiting, diarrhea, rash, pruritus, bronchospasm (especially with nebulized administration). * **Serious:** Anaphylactoid reactions, respiratory distress. ## Key Drug Interactions * **Activated Charcoal:** May bind to oral acetylcysteine, reducing its absorption. Administer oral acetylcysteine at least 1 hour after activated charcoal. * **Nitroglycerin:** Concurrent use may potentiate hypotension and headache due to vasodilation. Monitor blood pressure. ## Monitoring * **Acetaminophen Overdose:** Serum acetaminophen levels, liver function tests (ALT, AST, bilirubin, PT/INR), glucose, and renal function. Clinical signs of hepatotoxicity. * **Mucolytic Use:** Respiratory status, sputum viscosity, signs of bronchospasm. ## Clinical Pearls * The odor of acetylcysteine is unpleasant (sulfur-like) and can cause nausea and vomiting, particularly with oral administration. * For IV acetylcysteine in acetaminophen overdose, pre-treatment with an antihistamine may be considered to reduce the risk of anaphylactoid reactions. * Nebulized acetylcysteine can sometimes thicken secretions or induce bronchospasm. Co-administration with a bronchodilator may be beneficial. * The antidote efficacy for acetaminophen overdose is highest when initiated within 8 hours of ingestion. * Ensure adequate hydration when using acetylcysteine, especially for respiratory indications. *** **Disclaimer:** This information is intended for clinical use and is not a substitute for professional medical advice. Always consult the most current prescribing information and relevant clinical guidelines before making treatment decisions. Dosing and management may vary based on individual patient factors, institutional protocols, and evolving medical knowledge.