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# Acetylcysteine
## Overview
Acetylcysteine (NAC) is an antidote for acetaminophen overdose and a mucolytic agent. It works by replenishing glutathione stores, which are depleted during acetaminophen metabolism, and by breaking disulfide bonds in mucus.
## Primary Indications
* **Acetaminophen overdose:** 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 (IV):** A common protocol involves a 3-bag regimen:
* Loading dose: 150 mg/kg infused over 1 hour.
* Second dose: 50 mg/kg infused over 4 hours.
* Third dose: 100 mg/kg infused over 16 hours.
* Maximum total dose: Typically around 300 mg/kg over the 20-hour period, but individual protocols may vary.
* **Oral (PO):**
* Loading dose: 140 mg/kg.
* Subsequent doses: 70 mg/kg every 4 hours for 17 doses (total of 18 doses).
* Maximum single oral dose: Not to exceed 1000 mg.
**Mucolytic (Inhaled):**
* 3-10 mL of a 20% solution or 6-10 mL of a 10% solution, nebulized every 2-6 hours.
* Maximum frequency: Typically not more than every 2-4 hours, depending on patient tolerance and clinical response.
## Pediatric Dosing
**Acetaminophen Overdose (IV):**
* Dosing is the same as for adults (150 mg/kg IV over 1 hour, then 50 mg/kg IV over 4 hours, then 100 mg/kg IV over 16 hours).
* Weight-based dosing should be used for accurate calculation, especially in younger children.
**Acetaminophen Overdose (Oral):**
* Dosing is the same as for adults (140 mg/kg PO loading dose, then 70 mg/kg PO every 4 hours for 17 doses).
**Mucolytic (Inhaled):**
* Generally 1-10 mL of a 20% solution or 2-5 mL of a 10% solution, nebulized every 2-6 hours. Dosing depends on age and clinical response.
## Dose Adjustments
* **Renal Impairment:** No specific dose adjustment is universally established for IV or inhaled use. Caution is advised, especially with high IV doses due to potential fluid overload.
* **Hepatic Impairment:** No specific dose adjustment is universally established for IV or inhaled use. Close monitoring is essential.
## Contraindications
* Known hypersensitivity to acetylcysteine or any component of the formulation.
## Adverse Effects
* **IV:** Anaphylactoid reactions (rash, pruritus, bronchospasm, angioedema, hypotension), nausea, vomiting. Reactions are more common with rapid infusion.
* **Inhaled:** Bronchospasm (especially in asthmatics), nausea, vomiting, stomatitis, rhinorrhea, urticaria.
* **Oral:** Nausea, vomiting, diarrhea.
## Key Drug Interactions
* **Activated Charcoal:** Can adsorb oral acetylcysteine, reducing its absorption. Separate administration by at least 1 hour.
* **Nitroglycerin:** May potentiate the vasodilatory effects of nitroglycerin, leading to hypotension.
## Monitoring
* **Acetaminophen Overdose:**
* Serum acetaminophen levels.
* Liver function tests (ALT, AST, bilirubin, INR).
* Renal function.
* Electrolytes.
* Clinical signs of anaphylactoid reaction (vital signs, rash, shortness of breath).
* **Mucolytic:**
* Respiratory status (lung sounds, work of breathing, sputum production).
* Bronchospasm.
## Clinical Pearls
* For IV acetylcysteine in acetaminophen overdose, a delay in initiating treatment beyond 8-10 hours after ingestion significantly reduces its efficacy.
* Premedication with an H1 antagonist (e.g., diphenhydramine) may be considered to reduce the incidence of anaphylactoid reactions with IV acetylcysteine.
* Inhaled acetylcysteine may cause bronchospasm; co-administration with a bronchodilator is often recommended, particularly in patients with reactive airway disease.
* Oral acetylcysteine has a characteristic sulfur odor, which can lead to poor patient compliance due to unpleasant taste and smell.
**Disclaimer:** This information is intended for healthcare professionals and is a summary. Always consult the most current prescribing information, local protocols, and patient-specific factors before making any clinical decisions.
