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# Acetylcysteine
## Overview
Acetylcysteine (N-acetylcysteine, NAC) is a mucolytic agent and an antidote for acetaminophen overdose. It works by replenishing glutathione stores and directly binding to the reactive metabolite of acetaminophen.
## Primary Indications
* Acetaminophen overdose
* Adjunctive treatment for mucus plugging in respiratory conditions (e.g., cystic fibrosis, chronic bronchitis, pneumonia)
## Adult Dosing
**Acetaminophen Overdose:**
* **Intravenous (IV):** Loading dose: 150 mg/kg IV infused over 1 hour. Maintenance infusion: 12.5 mg/kg/hr IV for 4 hours, followed by 6.25 mg/kg/hr IV for 16 hours. Total duration: 21 hours.
* Maximum loading dose: Typically not to exceed 150 mg/kg in a single hour, but further maximums may vary by protocol.
* Maximum maintenance dose: 12.5 mg/kg/hr.
* **Oral:** 140 mg/kg orally every 4 hours for 17 doses.
**Mucolytic Therapy:**
* **Inhaled:** 1-10 mL of a 20% solution or 2-10 mL of a 10% solution nebulized every 2-6 hours as needed.
* **Oral:** 200 mg twice daily to 600 mg three times daily.
## Pediatric Dosing
**Acetaminophen Overdose:**
* **Intravenous (IV):** Same as adult dosing (150 mg/kg IV over 1 hour, followed by 12.5 mg/kg/hr IV for 4 hours, then 6.25 mg/kg/hr IV for 16 hours). Dosing should be weight-based.
* **Oral:** 140 mg/kg orally every 4 hours for 17 doses.
**Mucolytic Therapy:**
* **Inhaled:** 1-10 mL of a 10% solution or 5-10 mL of a 20% solution nebulized every 2-6 hours as needed.
## Dose Adjustments
* No specific dose adjustments are typically required for renal or hepatic impairment for acetaminophen overdose protocols, as the goal is to replenish glutathione. However, caution may be advised in severe impairment, and clinical judgment should be used.
## Contraindications
* Hypersensitivity to acetylcysteine or any component of the formulation.
* Consider in patients with active bronchospasm when used for mucolytic therapy.
## Adverse Effects
* **IV Acetaminophen Antidote:** Anaphylactoid reactions (most common, including rash, pruritus, bronchospasm, angioedema), nausea, vomiting, fever.
* **Inhaled:** Bronchospasm (especially in patients with asthma or hyperreactive airways), nausea, vomiting, stomatitis, rhinorrhea.
* **Oral:** Nausea, vomiting, diarrhea, abdominal pain.
## Key Drug Interactions
* **Activated Charcoal:** May adsorb oral acetylcysteine, reducing its efficacy. If both are used, separate administration by at least 1 hour.
* **Nitroglycerin:** May potentiate the vasodilatory effects of nitroglycerin, leading to hypotension. Monitor blood pressure.
## Monitoring
* **Acetaminophen Overdose:**
* Serum acetaminophen levels (especially if the time of ingestion is unknown or >24 hours).
* Liver function tests (AST, ALT, bilirubin, INR) at baseline and periodically (e.g., 24, 48, 72 hours).
* Prothrombin time (PT) or INR if liver injury is suspected.
* Renal function.
* Clinical signs of anaphylaxis during IV infusion.
* **Mucolytic Therapy:**
* Respiratory status (breath sounds, oxygen saturation, work of breathing).
* Bronchospasm.
## Clinical Pearls
* The IV antidote protocol is generally preferred for acetaminophen overdose due to better palatability and reduced risk of vomiting compared to oral administration.
* Anaphylactoid reactions to IV acetylcysteine are common but usually not a contraindication to continue therapy, especially in severe overdose. Slowing the infusion rate can mitigate symptoms.
* For inhaled acetylcysteine, premedication with a bronchodilator may be necessary for patients prone to bronchospasm.
* Intact mucus is less effective as an antidote than nebulized acetylcysteine.
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**Disclaimer:** This information is intended for healthcare professionals and should not be considered a substitute for professional medical advice. Always consult the most current prescribing information and relevant clinical guidelines for complete details on drug use, dosing, and safety.
