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# Acetylcysteine
## Overview
Acetylcysteine is an antidote for acetaminophen overdose and a mucolytic agent. It replenishes glutathione stores depleted by toxic acetaminophen metabolites. As a mucolytic, it breaks disulfide bonds in mucoproteins, decreasing mucus viscosity.
## Primary Indications
* **Acetaminophen Overdose:** Antidote to prevent or reduce liver toxicity.
* **Mucolytic:** To thin respiratory secretions in conditions like cystic fibrosis, chronic bronchitis, and pneumonia.
## Adult Dosing
**Acetaminophen Overdose (Intravenous):**
* **Loading Dose:** 150 mg/kg IV infused over 1 hour.
* **Second Infusion:** 50 mg/kg IV infused over 4 hours.
* **Third Infusion:** 100 mg/kg IV infused over 16 hours.
* **Total Duration:** 21 hours.
* **Maximum Dose:** Consult specific protocols; may be limited by total volume and concentration, especially with large body weight.
**Acetaminophen Overdose (Oral):**
* **Loading Dose:** 140 mg/kg PO.
* **Subsequent Doses:** 70 mg/kg PO every 4 hours for 17 doses (total of 18 doses).
* **Maximum Dose:** Generally not specified, but large volumes can be challenging.
**Mucolytic (Nebulized):**
* 3-5 mL of 20% solution or 6-10 mL of 10% solution via nebulizer every 2-6 hours.
* **Maximum Dose:** Dosing can vary based on clinical response and local protocol.
## Pediatric Dosing
**Acetaminophen Overdose (Intravenous):**
* Same weight-based dosing as adults:
* Loading Dose: 150 mg/kg IV infused over 1 hour.
* Second Infusion: 50 mg/kg IV infused over 4 hours.
* Third Infusion: 100 mg/kg IV infused over 16 hours.
* **Maximum Dose:** Consult specific protocols; may be limited by total volume and concentration, especially with very small infants.
**Acetaminophen Overdose (Oral):**
* Same weight-based dosing as adults:
* Loading Dose: 140 mg/kg PO.
* Subsequent Doses: 70 mg/kg PO every 4 hours for 17 doses.
**Mucolytic (Nebulized):**
* **Infants and Children < 4 years:** 1-2 mL of 20% solution or 2-4 mL of 10% solution via nebulizer every 2-6 hours.
* **Children > 4 years:** 3-5 mL of 20% solution or 6-10 mL of 10% solution via nebulizer every 2-6 hours.
* **Maximum Dose:** Dosing can vary based on clinical response and local protocol.
## Dose Adjustments
No specific dose adjustments are routinely recommended for renal or hepatic impairment in the context of acetaminophen overdose antidote therapy, as the benefit of preventing liver failure outweighs potential concerns. For mucolytic use, dose adjustments are typically based on clinical response and tolerability.
## Contraindications
* Hypersensitivity to acetylcysteine or any component of the formulation.
* Certain preparations may contain sodium or sulfite, which may be contraindicated in patients with known hypersensitivity or intolerance.
## Adverse Effects
**Intravenous:** Anaphylactoid reactions (rash, pruritus, urticaria, bronchospasm, dyspnea, angioedema), hypotension, tachycardia, flushing. Nausea and vomiting are common.
**Nebulized:** Bronchospasm (especially in asthmatics), stomatitis, nausea, vomiting, rhinorrhea.
## Key Drug Interactions
* **Activated Charcoal:** Can adsorb acetylcysteine, reducing its absorption when given orally for acetaminophen overdose. Separate administration by at least 1 hour.
* **Nitroglycerin:** Potential for additive hypotensive effects.
## Monitoring
* **Acetaminophen Overdose:**
* Acetaminophen levels (serial measurements).
* Liver function tests (AST, ALT, bilirubin, INR).
* Renal function (BUN, creatinine).
* Electrolytes.
* Blood glucose.
* Clinical signs of liver toxicity.
* **Mucolytic Use:**
* Respiratory status (wheezing, dyspnea, oxygen saturation).
* Sputum characteristics (viscosity, quantity).
* Potential for bronchospasm.
## Clinical Pearls
* For IV acetylcysteine in acetaminophen overdose, prompt initiation is crucial, especially if the overdose is known or suspected. The 21-hour regimen is standard.
* Anaphylactoid reactions to IV acetylcysteine are common and usually manageable with dose reduction, slowed infusion, or antihistamines/bronchodilators. Discontinuation is rarely necessary.
* Oral acetylcysteine has a strong, unpleasant odor (rotten eggs) and can cause significant nausea and vomiting, potentially limiting adherence. Anti-emetics may be beneficial.
* Nebulized acetylcysteine can induce bronchospasm. Consider co-administration of a bronchodilator (e.g., albuterol) prior to nebulization, especially in patients with reactive airway disease.
* The antidote efficacy of acetylcysteine is most pronounced when given within 8-10 hours of acetaminophen ingestion. However, it should still be administered even if the timeframe is exceeded, as it may still offer some benefit in preventing or reducing the severity of liver injury.
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**Disclaimer:** This information is intended for healthcare professionals and is not a substitute for professional medical advice. Always consult the most current prescribing information and institutional protocols before administering any medication.
