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# Acetylcysteine
## Overview
Acetylcysteine (NAC) is a mucolytic agent that decreases the viscosity of respiratory tract secretions. It is also used as an antidote for acetaminophen overdose.
## Primary Indications
* **Acetaminophen Overdose:** To prevent or treat liver damage.
* **Mucolytic:** To thin and loosen mucus secretions in patients with chronic obstructive pulmonary disease (COPD), cystic fibrosis, or bronchitis.
## Adult Dosing
**Acetaminophen Overdose:**
* **Intravenous (IV):** Typically a 3-bag, 72-hour protocol.
* **Loading Dose:** 150 mg/kg IV infused over 1 hour.
* **Second Dose:** 50 mg/kg IV infused over 16 hours.
* **Third Dose:** 100 mg/kg IV infused over the next 16 hours.
* **Maximum Dose:** Total daily dose should not exceed 150 mg/kg or 12 grams, whichever is less, for patients weighing over 100 kg. Higher doses may be used in severe ingestions at the discretion of the poison control center or treating physician.
* **Oral:** Typically a 17-dose protocol over 72 hours.
* **Loading Dose:** 140 mg/kg PO (maximum 13.3 grams).
* **Subsequent Doses:** 70 mg/kg PO every 4 hours for 17 doses (maximum 6.7 grams per dose).
* **Note:** Oral formulation has a significant emetic potential. IV administration is preferred if vomiting is present or if serum acetaminophen levels are elevated.
**Mucolytic:**
* **Nebulized:** 3-10 mL of a 20% solution or 6-10 mL of a 10% solution every 2-6 hours as needed.
* **Nebulized:** 1-2 mL of a 20% solution or 2-4 mL of a 10% solution every 2-6 hours as needed, often used for milder conditions.
* **Oral (Effervescent Tablets):** 200 mg orally twice daily or 200 mg orally three times daily. Some protocols may use up to 1200 mg/day.
* **Oral (Granules/Capsules):** 600 mg orally once daily or 200 mg orally three times daily.
## Pediatric Dosing
**Acetaminophen Overdose:**
* **Intravenous (IV):** Dosing is the same as adults (150 mg/kg loading, 50 mg/kg for 16 hours, then 100 mg/kg for 16 hours). Extreme caution is advised with weight-based calculations to avoid overdosing neonates.
* **Oral:** Dosing is the same as adults (140 mg/kg loading, 70 mg/kg every 4 hours for 17 doses).
**Mucolytic:**
* **Nebulized:**
* **Infants and children up to 1 year:** 1 mL of a 20% solution or 2 mL of a 10% solution every 2-6 hours.
* **Children 1-6 years:** 3-5 mL of a 20% solution or 6-10 mL of a 10% solution every 2-6 hours.
* **Children >6 years:** 5-10 mL of a 20% solution or 10 mL of a 10% solution every 2-6 hours.
* **Oral:** Dosing varies based on formulation and indication. Consult product labeling or local protocols. For example, for cystic fibrosis, doses up to 1200 mg/day have been used in children.
## Dose Adjustments
No specific dose adjustments are typically required for hepatic or renal impairment when used as an antidote for acetaminophen overdose, as the drug is rapidly distributed and metabolized. For mucolytic use, dose adjustments are generally not needed, but frequency or concentration may be modified based on patient response and tolerance.
## Contraindications
* Hypersensitivity to acetylcysteine or any component of the formulation.
* Acute asthma exacerbations (for nebulized use, though benefits may outweigh risks in severe bronchospasm).
## Adverse Effects
* **Nebulized:** Bronchospasm, urticaria, nausea, vomiting, stomatitis, rhinorrhea, drowsiness. Bronchospasm is a significant concern, especially in asthmatics.
* **Intravenous (IV):** Anaphylactoid reactions (rash, pruritus, angioedema, bronchospasm, dyspnea), nausea, vomiting, tachycardia, hypotension. Infusion rate can influence the risk of anaphylactoid reactions.
* **Oral:** Nausea, vomiting, diarrhea, abdominal pain, stomatitis.
## Key Drug Interactions
* **Activated Charcoal:** May adsorb oral acetylcysteine, potentially reducing its effectiveness in acetaminophen overdose. Administer NAC at least 1 hour after activated charcoal.
* **Nitroglycerin:** Concurrent use may potentiate the vasodilatory effects of nitroglycerin, leading to hypotension. Monitor blood pressure closely.
## Monitoring
* **Acetaminophen Overdose:**
* Serum acetaminophen levels (repeatedly).
* Liver function tests (ALT, AST, bilirubin, INR) at baseline and regularly during treatment.
* Renal function and electrolytes.
* Clinical signs of liver toxicity (jaundice, encephalopathy).
* **Mucolytic Use:**
* Respiratory status (breath sounds, sputum production, work of breathing).
* Symptomatic improvement.
* Adverse effects, particularly bronchospasm.
## Clinical Pearls
* NAC is most effective in acetaminophen overdose when initiated within 8 hours of ingestion. However, it should be administered regardless of the time of presentation, as it can still provide benefit, especially in delayed presentations or severe ingestions.
* The characteristic "rotten egg" smell of acetylcysteine can cause nausea and vomiting. Administering it with a flavored beverage or using an antiemetic may improve tolerance for oral administration.
* For nebulized acetylcysteine, consider co-administration with a bronchodilator (e.g., albuterol) to mitigate the risk of bronchospasm.
* Dilution of IV acetylcysteine is often recommended to reduce the risk of anaphylactoid reactions and fluid overload, especially in children. Specific dilution guidelines should be followed per institutional protocol or manufacturer's recommendations.
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*Disclaimer: This information is intended for healthcare professionals. Always consult the most current prescribing information, institutional protocols, and patient-specific factors before making clinical decisions.*
