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# Acetylcysteine
## Overview
Acetylcysteine is a mucolytic agent that breaks disulfide bonds in mucus, decreasing its viscosity. It is also an antidote for acetaminophen overdose by replenishing glutathione stores.
## Primary Indications
* **Acetaminophen overdose:** To prevent or treat hepatotoxicity.
* **Thick bronchial secretions:** In conditions like cystic fibrosis, COPD, and pneumonia.
## Adult Dosing
### Acetaminophen Overdose
* **Oral:**
* Loading dose: 140 mg/kg.
* Subsequent doses: 70 mg/kg every 4 hours for 17 doses.
* Maximum single dose: Not explicitly defined for oral, but total daily intake can be substantial.
* **Intravenous (IV):**
* Loading dose: 150 mg/kg over 60 minutes.
* Second infusion: 50 mg/kg over the next 4 hours.
* Third infusion: 100 mg/kg over the next 16 hours.
* Maximum single dose: 150 mg/kg.
* *Note: IV dosing protocols may vary by institution. Some protocols use higher continuous infusion rates.*
### Thick Bronchial Secretions
* **Inhaled:** 10% solution: 3-5 mL every 6-8 hours. 20% solution: 2-5 mL every 6-8 hours.
* **Oral:** 200-600 mg once or twice daily. (e.g., 200 mg BID to TID, or 600 mg QD).
## Pediatric Dosing
### Acetaminophen Overdose
* **Oral:** Same as adult: 140 mg/kg loading dose, then 70 mg/kg every 4 hours for 17 doses.
* **Intravenous (IV):** Same as adult: 150 mg/kg over 60 minutes, then 50 mg/kg over 4 hours, then 100 mg/kg over 16 hours.
* *Note: For children weighing less than 30 kg, the total volume of IV NAC may be excessive. Consider dilution with normal saline or a 5% dextrose solution to reduce the risk of fluid overload. Dosing is generally weight-based and not capped at adult maximums in the initial phase.*
### Thick Bronchial Secretions
* **Inhaled:**
* 10% solution: 1-2 mL every 6-8 hours.
* 20% solution: 1-2 mL every 6-8 hours.
* **Oral:** 50-100 mg/kg/day divided into 2-4 doses, not to exceed 600 mg/day. (e.g., 50-100 mg BID to QID).
## Dose Adjustments
* No dose adjustments are typically needed for renal or hepatic impairment when used for acetaminophen overdose.
* For inhaled use, dose is adjusted based on concentration and response.
## Contraindications
* Known hypersensitivity to acetylcysteine.
* Use with caution in patients with asthma or history of bronchospasm due to potential for bronchoconstriction.
## Adverse Effects
* **Inhaled:** Bronchospasm, bronchoconstriction, increased sputum volume, stomatitis, rhinorrhea, nausea, vomiting.
* **Intravenous:** Anaphylactoid reactions (urticaria, rash, pruritus, angioedema, bronchospasm, dyspnea, hypotension), fever, chills. Nausea and vomiting can occur, especially with oral administration.
## Key Drug Interactions
* **Activated charcoal:** Can adsorb oral acetylcysteine, reducing its efficacy in acetaminophen overdose. Administer charcoal at least 1 hour *before* or 1 hour *after* oral acetylcysteine.
* **Nitroglycerin:** May potentiate the vasodilatory effects of nitroglycerin, leading to hypotension and headache.
## Monitoring
* **Acetaminophen Overdose:**
* Serum acetaminophen levels (obtain at least 4 hours post-ingestion, and repeat as needed).
* Liver function tests (ALT, AST, bilirubin, PT/INR) starting at 24 hours and monitored daily for at least 3 days.
* Renal function and electrolytes.
* Clinical signs of hepatotoxicity.
* **Thick Bronchial Secretions:**
* Pulmonary status, subjective improvement in mucus expectoration.
* Monitor for bronchospasm, especially in patients with reactive airway disease.
## Clinical Pearls
* For acetaminophen overdose, prompt initiation of acetylcysteine is crucial, especially if acetaminophen levels are in the toxic range or ingestion time is unknown.
* IV acetylcysteine for acetaminophen overdose can cause anaphylactoid reactions. Monitor patients closely during infusions, particularly the first few hours. Antihistamines may be considered prophylactically or for treatment of mild reactions.
* N-acetylcysteine has antioxidant properties and is being investigated for other conditions, but evidence is limited.
* When using inhaled acetylcysteine, consider co-administration with a bronchodilator if the patient has reactive airway disease.
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*Please verify current prescribing information and institutional protocols before administering medications.*
