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# Acetylcysteine
## Overview
Acetylcysteine (N-acetyl-L-cysteine) functions as a mucolytic by splitting disulfide bonds in mucoproteins and as a hepatoprotective agent by restoring hepatic glutathione stores.
## Primary Indications
* **Acetaminophen overdose:** Provision of glutathione substrate for toxic metabolite (NAPQI) detoxification.
* **Mucolytic therapy:** Adjunct for abnormal, viscid, or inspissated mucous secretions (e.g., COPD, cystic fibrosis).
* **Contrast-induced nephropathy (off-label):** Prophylaxis in high-risk patients.
## Adult Dosing
* **Acetaminophen Overdose (IV - Acetadote protocol):**
* 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.
* *Note: Follow local protocol/nomogram for extension if levels remain detectable.*
* **Mucolytic (Inhalation):** 1–10 mL of 20% solution or 2–20 mL of 10% solution via nebulizer, 3–4 times daily.
## Pediatric Dosing
* **Acetaminophen Overdose (IV):** Identical mg/kg dosing as adults; adjust fluid volume based on patient weight/fluid status to avoid hyponatremia.
* **Mucolytic (Inhalation):** 3–5 mL of 20% solution or 6–10 mL of 10% solution via nebulizer, 3–4 times daily.
## Dose Adjustments
* **Renal/Hepatic:** No formal dose adjustment required for mucolytic use. For IV acetaminophen toxicity, clinical signs and repeat serum levels dictate continuation of therapy.
* **Fluid overload:** Use smaller fluid volumes in pediatric or cardiac-compromised patients to prevent hyponatremia.
## Contraindications
* **Hypersensitivity:** Known hypersensitivity to acetylcysteine.
* **Asthma:** Use with caution in patients with asthma; bronchodilator pretreatment (e.g., albuterol) is recommended to prevent bronchospasm during inhalation therapy.
## Adverse Effects
* **Inhalation:** Bronchospasm, stomatitis, rhinorrhea, nausea, vomiting.
* **IV (Anaphylactoid reactions):** Flushing, pruritus, rash, angioedema, hypotension, or respiratory distress (usually dose/rate-dependent). Stop infusion and treat symptoms (antihistamines, fluids).
## Key Drug Interactions
* **Activated Charcoal:** May adsorb acetylcysteine. Administer charcoal at least 1 hour before oral acetylcysteine; if both are already given, usually proceed with acetylcysteine therapy.
* **Incompatible mixtures:** Do not mix inhaled acetylcysteine with tetracyclines, erythromycin, amphotericin B, or ampicillin due to physical incompatibility.
## Monitoring
* **Acetaminophen Toxicity:** Serum acetaminophen levels, AST/ALT, bilirubin, prothrombin time (INR), creatinine, and electrolytes.
* **Mucolytic:** Respiratory effort, cough frequency, sputum viscosity/clearing.
* **IV Infusion:** Monitor closely for anaphylactoid reactions throughout administration.
## Clinical Pearls
* **Oral vs. IV:** Oral administration is equally efficacious for acetaminophen overdose but requires antiemetics due to poor tolerability.
* **Smell:** Nebulized acetylcysteine may have a sulfurous (rotten egg) odor; inform patients this is normal.
* **Stability:** Once a vial is opened, it should be stored in a refrigerator and used within 96 hours; discoloration (light purple) does not affect potency.
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**Disclaimer:** This information is for educational purposes. Clinical protocols for acetaminophen overdose vary by institution (e.g., 20-hour vs. 21-hour protocols). Always verify specific dosing and safety data through institutional guidelines, current package inserts, or clinical pharmacists before prescribing or administering.
