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# Acetylcysteine
## Overview
Acetylcysteine (N-acetyl-L-cysteine) is a derivative of the amino acid L-cysteine. It functions primarily as a mucolytic agent by splitting disulfide bonds in mucous glycoproteins and as a glutathione precursor used to treat acetaminophen (APAP) toxicity.
## Primary Indications
* **Acetaminophen toxicity:** Antidote for hepatotoxicity.
* **Mucolytic therapy:** Adjunct for abnormal, viscid, or inspissated mucous secretions (e.g., chronic bronchopulmonary disease, cystic fibrosis).
* **Contrast-induced nephropathy (CIN):** Prophylaxis (evidence is controversial/weak).
## Adult Dosing
* **Acetaminophen Toxicity:** 140 mg/kg loading dose orally, followed by 70 mg/kg every 4 hours for 17 additional doses. **IV Protocol (Acetadote):** 150 mg/kg over 60 mins, then 50 mg/kg over 4 hours, then 100 mg/kg over 16 hours. (Note: IV protocols vary by institution/toxicity nomogram).
* **Mucolytic (Inhalation):** 1–10 mL of 20% solution or 2–20 mL of 10% solution via nebulizer every 2–6 hours.
* **Mucolytic (Instillation):** 1–2 mL of 10–20% solution every 1–4 hours.
## Pediatric Dosing
* **Acetaminophen Toxicity:** Same weight-based loading and maintenance doses as adults.
* **Mucolytic:** 3–5 mL of 20% solution or 6–10 mL of 10% solution via nebulizer 3–4 times daily.
## Dose Adjustments
* **Renal/Hepatic:** No specific adjustments for mucolytic use. For APAP toxicity, dosage is strictly weight-based regardless of renal/hepatic function, though total fluid volume in IV administration may require adjustment in fluid-restricted patients.
## Contraindications
* **Hypersensitivity:** Known hypersensitivity to acetylcysteine.
* **Oral/IV Use:** No absolute contraindications for life-threatening APAP toxicity.
* **Inhalation:** Use with caution in patients with asthma or severe bronchospasm.
## Adverse Effects
* **IV/Oral:** Anaphylactoid reactions (rash, hypotension, wheezing), nausea, vomiting, and flushing. Reaction is more common with IV loading dose and is often infusion-rate dependent.
* **Inhalation:** Bronchospasm (can be severe), stomatitis, rhinorrhea, and unpleasant odor (sulfur).
## Key Drug Interactions
* **Activated Charcoal:** May adsorb acetylcysteine. Administer charcoal first and consider increasing the acetylcysteine dose if significant charcoal is present in the stomach.
* **Incompatible Medications:** Do not mix inhaled acetylcysteine with tetracyclines or erythromycin lactobionate in the same nebulizer.
## Monitoring
* **APAP Toxicity:** Serial serum APAP levels (if using Rumack-Matthew nomogram), ALT, AST, bilirubin, prothrombin time, and INR.
* **Inhalation:** Monitor for bronchospasm; ensure a bronchodilator (e.g., albuterol) is available for rescue.
* **General:** Monitor for signs of anaphylactoid reactions during IV infusion.
## Clinical Pearls
* **Odor:** The drug has a strong sulfur (rotten egg) smell, which may cause nausea. Diluting the oral dose in juice or soda can improve palatability.
* **Asthma:** If utilizing as a mucolytic in reactive airway disease, always pretreat with a fast-acting bronchodilator.
* **IV Safety:** Anaphylactoid reactions usually occur during the initial loading dose period and are managed by slowing the infusion rate and administering antihistamines/corticosteroids.
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**Educational Disclaimer:** This information is for educational purposes only. Clinical dosing protocols, especially for acetaminophen toxicity, vary significantly by institution and local poison control guidelines. Always verify current prescribing information, institutional protocols, and patient-specific factors before administration.
