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# Acetylcysteine
## Overview
Acetylcysteine is an N-acetyl derivative of the amino acid L-cysteine. It functions as a mucolytic agent by splitting disulfide bonds in mucoproteins and as a glutathione precursor/substitute in acetaminophen overdose.
## Primary Indications
* **Acetaminophen Overdose:** Antidote to prevent hepatotoxicity.
* **Mucolytic Therapy:** Adjunct in bronchopulmonary conditions (e.g., cystic fibrosis, COPD, acute bronchitis).
* **Contrast-Induced Nephropathy (Off-label):** Prophylaxis in high-risk patients.
## Adult Dosing
### Acetaminophen Overdose (IV Protocol - Acetadote)
Administered as a 3-bag protocol:
1. **Loading Dose:** 150 mg/kg in 200 mL D5W over 60 minutes.
2. **Second Dose:** 50 mg/kg in 500 mL D5W over 4 hours.
3. **Third Dose:** 100 mg/kg in 1000 mL D5W over 16 hours.
* *Note: Follow institutional protocol; dose may be extended if acetaminophen/AST/ALT remain elevated.*
### Mucolytic (Inhalation)
* **Nebulized:** 3–5 mL of 20% solution or 6–10 mL of 10% solution 3–4 times daily via face mask or mouthpiece.
## Pediatric Dosing
### Acetaminophen Overdose (IV Protocol)
Dosing is weight-based (typically follows the same 150/50/100 mg/kg protocol as adults). Fluid volume must be adjusted based on the patient's weight and fluid restrictions. Consult a pediatric dosing chart/nomogram for diluent volumes.
### Mucolytic (Inhalation)
* **Infants/Children:** 1–2 mL of 20% solution or 2–4 mL of 10% solution via nebulizer 3–4 times daily.
## Dose Adjustments
* **Hepatic Impairment:** No dose adjustment for mucolytic use. For acetaminophen overdose, extend the final infusion time or reduce rate if fluid overload is a concern.
* **Renal Impairment:** No standard adjustment, but monitor for fluid overload during IV administration.
## Contraindications
* **Hypersensitivity:** Known reaction to acetylcysteine.
* **Inhalation:** Use with caution in patients with asthma due to potential for bronchospasm.
## Adverse Effects
* **IV:** Anaphylactoid reactions (flushing, pruritus, rash, angioedema, hypotension), nausea, and vomiting.
* **Inhalation:** Bronchospasm (especially in asthmatics - pretreatment with a beta-agonist is recommended), stomatitis, rhinorrhea, and unpleasant odor (rotten egg smell due to sulfur).
## Key Drug Interactions
* **Beta-agonists:** Should be administered prior to inhaled acetylcysteine to prevent bronchospasm.
* **Incompatible Drugs:** Physically incompatible with certain antibiotics (e.g., tetracyclines, erythromycin, amphotericin B) if mixed in the same nebulizer.
## Monitoring
* **Acetaminophen Overdose:** Serum acetaminophen levels (Rumack-Matthew nomogram), AST, ALT, billirubin, PT/INR, and creatinine. Monitor for signs of anaphylactoid reaction during the loading dose (stop infusion and treat if occur).
* **Respiratory:** Monitor airway patency and cough frequency in mucolytic patients; ensure suction is available if copious secretions are mobilized.
## Clinical Pearls
* **Odor:** The "rotten egg" smell is characteristic; inform the patient/caregiver that this is normal.
* **IV Anaphylactoid Reactions:** These are non-IgE mediated and are usually infusion-rate dependent. If a mild reaction occurs, slowing the rate is often sufficient.
* **Formulation:** Ensure the correct concentration is used for the intended route (Do not use inhalation solution for IV administration if the product is not sterile/appropriate for parenteral use).
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**Educational Disclaimer:** This information is for educational purposes only. Clinical protocols for acetaminophen overdose vary by institution and regional poison control guidelines. Always consult current institutional standards of care, the prescribing information (package insert), and a clinical pharmacist before prescribing or administering medication.
