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# Acetylcysteine
## Overview
Acetylcysteine (NAC) is an mucolytic agent and an antidote for acetaminophen overdose. It works by breaking disulfide bonds in mucus, reducing its viscosity. In acetaminophen overdose, it replenishes glutathione stores.
## Primary Indications
* Acetaminophen overdose
* Thick bronchial secretions (e.g., in cystic fibrosis, chronic bronchitis)
## Adult Dosing
**Acetaminophen Overdose:**
* **IV:** Typically a 3-bag protocol.
* **Loading Dose:** 150 mg/kg IV over 1 hour.
* **Second Infusion:** 50 mg/kg IV over 4 hours.
* **Third Infusion:** 100 mg/kg IV over 16 hours.
* Maximum dose: Commonly cited maximum is 300 mg/kg total, though some protocols may use higher amounts in severe cases.
* **Oral:** (Less common, associated with higher rates of nausea/vomiting)
* **Loading Dose:** 140 mg/kg orally.
* **Subsequent Doses:** 70 mg/kg orally every 4 hours for 17 doses.
* Maximum dose: 140 mg/kg initial, then 70 mg/kg up to 17 times.
**Thick Bronchial Secretions:**
* **Inhaled:** 10% solution: 3-5 mL via nebulization every 2-6 hours. 20% solution: 3-5 mL via nebulization every 2-6 hours.
* **Oral:** 200 mg twice daily or 600 mg once daily.
## Pediatric Dosing
**Acetaminophen Overdose:**
* Dosing is weight-based, identical to adult IV dosing. **Caution:** Ensure appropriate dilution for smaller pediatric patients to avoid fluid overload.
* **Oral:** Dosing is weight-based, identical to adult oral dosing.
**Thick Bronchial Secretions:**
* **Inhaled:**
* **< 1 year:** 1-2 mL of 10% solution via nebulization every 2-6 hours.
* **> 1 year:** 3-5 mL of 10% solution via nebulization every 2-6 hours.
* **Oral:** Dosing varies; consult specific pediatric guidelines. A common regimen is 50-100 mg/kg/day divided into 2-4 doses.
## Dose Adjustments
No dose adjustment is typically required for renal or hepatic impairment, but caution and monitoring are advised, especially in overdose scenarios.
## Contraindications
* Known hypersensitivity to acetylcysteine or any component of the formulation.
## Adverse Effects
**IV Administration (Overdose):**
* Anaphylactoid reactions (rash, urticaria, pruritus, bronchospasm, angioedema) are most common. These are generally less severe and occur later than true anaphylaxis.
* Nausea and vomiting.
* Flushing.
* Tachycardia, hypotension.
**Inhaled Administration:**
* Bronchospasm (especially in patients with reactive airway disease).
* Stomatitis, rhinorrhea, nausea, vomiting.
**Oral Administration:**
* Nausea, vomiting, diarrhea.
* Rash.
## Key Drug Interactions
* **Activated Charcoal:** May adsorb oral acetylcysteine, reducing its absorption. Administer acetylcysteine at least 1 hour after activated charcoal if feasible.
* **Nitroglycerin:** May potentiate the vasodilatory effects of nitroglycerin. Monitor blood pressure.
## Monitoring
* **Acetaminophen Overdose:**
* Serum acetaminophen levels (serial monitoring is crucial).
* Liver function tests (AST, ALT, bilirubin, INR).
* Renal function.
* Glucose.
* Electrolytes.
* Signs and symptoms of anaphylactoid reaction.
* **Thick Bronchial Secretions:**
* Pulmonary status and effectiveness of secretion clearance.
* Bronchospasm.
## Clinical Pearls
* For IV acetylcysteine in acetaminophen overdose, administer the loading dose as rapidly as tolerated to achieve peak plasma concentrations.
* Anaphylactoid reactions to IV acetylcysteine can be managed with antihistamines and bronchodilators and do not usually necessitate discontinuation of the antidote.
* Pre-treatment with an antihistamine (e.g., diphenhydramine) may be considered for patients at risk of anaphylactoid reactions, especially those who have received acetylcysteine previously.
* Ensure adequate hydration for inhaled acetylcysteine to help mobilize secretions.
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*Disclaimer: This information is intended for clinical use and does not substitute for professional medical judgment. Always verify current prescribing information and local protocols before administering any medication.*
