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# Acetylcysteine
## Overview
Acetylcysteine (N-acetyl-L-cysteine) is a mucolytic agent and the specific antidote for acetaminophen (APAP) toxicity. It acts as a glutathione precursor, supporting detoxification of the reactive metabolite NAPQI.
## Primary Indications
* **Acetaminophen toxicity:** Management of acute ingestion or chronic/supratherapeutic ingestion.
* **Mucolytic therapy:** Adjunct in bronchopulmonary conditions (e.g., cystic fibrosis, COPD, acute bronchitis).
## Adult Dosing
* **Acetaminophen Toxicity (IV Protocol - 21-hour regimen):**
* Loading: 150 mg/kg in 200 mL D5W over 60 minutes.
* Second dose: 50 mg/kg in 500 mL D5W over 4 hours.
* Third dose: 100 mg/kg in 1000 mL D5W over 16 hours.
* **Mucolytic (Inhalation):** 3-5 mL of 20% solution or 6-10 mL of 10% solution via nebulizer 3-4 times daily.
## Pediatric Dosing
* **Acetaminophen Toxicity:** Dosage is weight-based and mirrors the adult IV protocol (150 mg/kg load, followed by 50 mg/kg, then 100 mg/kg). Diluent volumes must be adjusted based on fluid status/age.
* **Mucolytic (Inhalation):** 3-5 mL of 20% solution or 6-10 mL of 10% solution via nebulizer 3-4 times daily.
## Dose Adjustments
* **Fluid overload:** Reduce volume of IV diluents; must be calculated carefully in children and patients with congestive heart failure or renal dysfunction.
* **Hepatic impairment:** No standard adjustment required for APAP toxicity, but monitor closely as liver failure complicates fluid management.
## Contraindications
* Hypersensitivity to acetylcysteine or any component of the formulation.
* No absolute contraindications for APAP toxicity management (life-saving).
## Adverse Effects
* **IV/Systemic:** Anaphylactoid reactions (flushing, urticaria, angioedema, bronchospasm, hypotension). Common during the loading dose.
* **Inhalation:** Bronchospasm (pre-treat with short-acting beta-agonist), stomatitis, rhinorrhea, nausea, vomiting.
## Key Drug Interactions
* **Inhaled agents:** Do not mix in the same nebulizer with antibiotics; acetylcysteine can inactivate certain antimicrobials.
* **Activated charcoal:** May adsorb acetylcysteine if administered concurrently; administer charcoal first and then assess the need for acetylcysteine.
## Monitoring
* **APAP Toxicity:** Baseline and serial serum APAP levels, AST/ALT, INR, electrolytes, and renal function.
* **Tolerance:** Observe for anaphylactoid symptoms, especially during the loading dose. Stop infusion if reaction occurs and restart at a slower rate or with antihistamine premedication per institutional protocol.
## Clinical Pearls
* **Timeline:** Most effective when initiated within 8-10 hours of acute APAP ingestion.
* **Odor:** Aerosolized acetylcysteine has a characteristic odor of rotten eggs (sulfur) which may cause patient discomfort or nausea.
* **Nebulization:** Always provide a bronchodilator (e.g., albuterol) prior to or concurrent with inhaled acetylcysteine to prevent potential drug-induced bronchospasm.
* **Protocol:* Dosing regimens for APAP vary by institution (e.g., 20-hour vs 21-hour protocols). Always verify with local facility guidelines.
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**Educational Disclaimer:** This information is for educational purposes only. Always consult current institutional protocols, the package insert, and clinical decision support tools (e.g., Lexicomp, Micromedex) before prescribing or administering any medication.
