Acetylcysteine
N-acetyl-L-cysteine
Also known as: Mucomyst · Acetadote · NAC · ACC · Ilube · Parvolex · Fluimucil · N-acetylcysteine · N-acetyl-L-cysteine · 5052 acetylcysteinum · NSC-111180
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Acetaminophen toxicity | 140 mg/kg PO loading dose, followed by 70 mg/kg PO q6h | PO | q6h | For 7 treatments (up to 12-17 doses for massive ingestions) | 🌎 NA |
| Acetaminophen toxicity | 150 mg/kg PO or IV initially, then 50 mg/kg q4h | PO/IV | q4h | For 17 additional doses | 🌎 NA |
| Acetaminophen toxicity | 140 mg/kg PO loading dose, then 70 mg/kg PO every 6 hours | PO | q6h | For 7 treatments | 🌎 NA |
| Phenol toxicity | 140 mg/kg PO or IV initially, then 50 mg/kg q4h | PO/IV | q4h | For 3 days | 🌎 NA |
| Hepatotoxicity secondary to xylitol poisoning | 140-280 mg/kg loading dose IV or PO; followed by 70 mg/kg four times daily | IV/PO | q6h | — | 🌎 NA |
| Degenerative myelopathy (anecdotal) | 25 mg/kg PO q8h for 2 weeks, then q8h every other day | PO | q8h | Indefinitely (every other day after 2 weeks) | 🌎 NA |
| Mucolytic | nebulize 50 mg as a 2% (dilute with saline) solution over 30-60 min or instil directly into the trachea 1-2 ml of a 20% solution | Nebulization/Intratracheal | prn | As needed | 🌍 EU |
| Paracetamol poisoning | 140-280 mg/kg diluted to a 5% solution using 5% dextrose by slow i.v. infusion over 15-20 min, followed by further slow infusions of 70 mg/kg (similarly diluted) every 6 hours | IV | q6h | for at least 7 doses | 🌍 EU |
| KCS | 1 drop of the ophthalmic solution | topical | q6-8h | As directed | 🌍 EU |
- Acetaminophen toxicity: Dilute to 5% in dextrose or sterile water. May also be given slow IV over 15-20 minutes. Wait 2-3 hours after activated charcoal if giving PO.
- Phenol toxicity: May be partially effective to reduce hepatic and renal injury.
- Hepatotoxicity secondary to xylitol poisoning: Used as part of a comprehensive protocol including vitamin K, plasma, SAMe, vitamin E, and silymarin.
- Degenerative myelopathy (anecdotal): Dilute 20% solution to 5% with chicken broth. Used in conjunction with aminocaproic acid. Note: No treatment has been shown to be effective in published trials.
- Mucolytic: Dilute with saline for nebulization.
- Paracetamol poisoning: Administer after inducing emesis if appropriate (within 2 hours of ingestion). IV preferred for serious intoxications. Can be given PO but must be diluted to improve palatability.
- KCS: Rarely used now for this indication.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Acetaminophen toxicity | 140 mg/kg PO loading dose, followed by 70 mg/kg PO four times daily (q6h) | PO | q6h | For 7 treatments (up to 12-17 doses for massive ingestions) | 🌎 NA |
| Phenol toxicity | 140 mg/kg PO or IV initially, then 50 mg/kg q4h | PO/IV | q4h | For 3 days | 🌎 NA |
| Adjunctive treatment of hepatic lipidosis | 140 mg/kg IV over 20 minutes, then 70 mg/kg IV q12h | IV | q12h | — | 🌎 NA |
| Mucolytic | nebulize 50 mg as a 2% (dilute with saline) solution over 30-60 min or instil directly into the trachea 1-2 ml of a 20% solution | Nebulization/Intratracheal | prn | As needed | 🌍 EU |
| Paracetamol poisoning | 140-280 mg/kg diluted to a 5% solution using 5% dextrose by slow i.v. infusion over 15-20 min, followed by further slow infusions of 70 mg/kg (similarly diluted) every 6 hours | IV | q6h | for at least 7 doses | 🌍 EU |
| KCS | 1 drop of the ophthalmic solution | topical | q6-8h | As directed | 🌍 EU |
- Acetaminophen toxicity: Dilute to 5% in dextrose or sterile water. May also be given slow IV over 15-20 minutes. Wait 2-3 hours after activated charcoal if giving PO.
- Phenol toxicity: May be partially effective to reduce hepatic and renal injury.
- Adjunctive treatment of hepatic lipidosis: Dilute 10% NAC with saline 1:4 and administer IV using a 0.25 micron filter.
- Mucolytic: Dilute with saline for nebulization.
- Paracetamol poisoning: IV administration is strongly preferred in cats as bioavailability is reduced with oral administration.
- KCS: Rarely used now for this indication.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| To help break up chondroids in the guttural pouch | Instill 20% solution | Local instillation | — | — | 🌎 NA |
| Meconium impaction in neonatal foals | 8 grams in 20 g sodium bicarbonate in 200 mL water (pH of 7.6), give as enema as needed to effect | Enema | PRN | — | 🌎 NA |
| Meconium impaction in neonatal foals | Infuse slowly 100-200 mL of 4% acetylcysteine solution and retain for 30-45 minutes | Retention enema | Once | Retain 30-45 minutes | 🌎 NA |
- Meconium impaction in neonatal foals: Use a 30 French Foley catheter with a 30 cc bulb. Monitor for possible bladder distention.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Acetylcysteine (often referred to as NAC) is a highly versatile therapeutic agent in veterinary medicine. It is most prominently utilized as a life-saving antidote for acetaminophen (paracetamol) toxicity, particularly in cats and dogs, where it prevents severe hepatic necrosis and methemoglobinemia.
Beyond its antidotal properties, acetylcysteine is a potent mucolytic agent. When administered into the respiratory tract, it effectively breaks down thick, viscous mucus, aiding in the clearance of respiratory secretions.
Clinical Applications:
- Toxicology: Primary treatment for acetaminophen, xylitol, and phenol toxicities.
- Respiratory: Used via nebulization or intratracheal instillation to treat chronic upper respiratory diseases or conditions with heavy mucus burden.
- Ophthalmic: Applied topically to halt the progression of "melting" corneal ulcers by inhibiting collagenases.
- Equine Medicine: Used locally to dissolve chondroids in the guttural pouch and administered as an enema for refractory meconium impactions in neonatal foals.
- Internal Medicine: Used adjunctively for feline hepatic lipidosis and anecdotally for canine degenerative myelopathy.
Mechanism of action
Antidote Mechanism (Hepatoprotection): Acetaminophen is metabolized in the liver to a highly reactive and toxic intermediate called NAPQI (N-acetyl-p-benzoquinone imine). Normally, NAPQI is safely conjugated by endogenous glutathione. In an overdose, glutathione is rapidly depleted, allowing NAPQI to cause severe oxidative stress and hepatocellular necrosis. Acetylcysteine acts as a glutathione precursor and provides an alternate sulfhydryl substrate to conjugate directly with NAPQI, thereby neutralizing the toxin and restoring cellular antioxidant defenses.
Mucolytic Mechanism: The free sulfhydryl group (-SH) on the acetylcysteine molecule directly interacts with mucoproteins in respiratory secretions. It cleaves the disulfide bonds linking these proteins, which drastically reduces the viscosity of both purulent and non-purulent mucus. This effect is optimal in an alkaline environment (pH 7-9). It has no effect on living tissue or fibrin.
Safety & warnings
Contraindications
- Hypersensitivity to the drug (specifically for pulmonary indications)
Adverse effects
- Nausea and vomiting (especially with oral administration due to poor palatability)
- Urticaria (rare)
- Bronchospasm, chest tightness, and bronchial/tracheal irritation (when inhaled)
- Blood pressure changes and allergic reactions (reported with IV boluses in humans)
Precautions
Use with caution in animals with pre-existing bronchospastic diseases (e.g., feline asthma) when administering via the pulmonary route, as it may trigger bronchospasm. Oral administration can be challenging due to the extremely foul taste and odor (sulfur/rotten eggs); administration via a gastric or duodenal tube is often necessary. If using the inhalation solution for intravenous administration, it is highly recommended to use a 0.2-micron in-line filter. Use caution in nursing dams as it is unknown if the drug enters milk.
Drug interactions
May adsorb orally administered acetylcysteine, potentially reducing its systemic absorption and efficacy. A 2-3 hour wait between charcoal and oral acetylcysteine is recommended, or acetylcysteine should be given intravenously.
Monitoring
- Hepatic enzymes (especially in dogs)
- Acetaminophen levels (if available)
- Hemogram, specifically monitoring methemoglobin values (especially critical in cats)
- Serum electrolytes
- Hydration status
Pharmacokinetics
Absorption
Well absorbed from the gastrointestinal tract when administered orally.
Distribution
When administered via nebulization or intratracheally, most of the drug remains localized in the pulmonary tract to participate in sulfhydryl-disulfide reactions; the remainder is systemically absorbed.
Metabolism
Absorbed drug is rapidly deacetylated into the amino acid cysteine in the liver, which is then further metabolized.
Overdose
Acetylcysteine is considered quite safe in overdose situations. The LD50 in dogs is reported to be 1 g/kg orally and 700 mg/kg intravenously. Massive overdoses may result in gastrointestinal distress (nausea, vomiting) or hypersensitivity reactions, but life-threatening toxicity from the drug itself is rare.
Available products
Formulations
- Injection: 20% (200 mg/mL)
- Oral/Inhalation Solution: 10% and 20%
- Oral capsules: 600 mg (OTC nutritional supplement)
Human-labeled
- Acetylcysteine injection: 20% (200 mg/mL) in 30 mL single-dose vials (Acetadote)
- Acetylcysteine Oral Solution: 10% & 20% (Mucomyst)
- Acetylcysteine Inhalation Solution: 10% & 20% (Mucomyst)
- N-Acetylcysteine (NAC) 600 mg capsules (OTC nutritional supplement)
Regulatory status
Human authorized products used under the cascade.
Human authorized products used under the cascade.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Unopened vials should be stored at room temperature (15-30°C). Once opened, vials must be refrigerated and used within 96 hours (products labeled specifically for IV use should be used within 24 hours). Acetylcysteine is incompatible with oxidizing agents and can liberate hydrogen sulfide when exposed to rubber, copper, or iron. It is incompatible in solution with amphotericin B, ampicillin, erythromycin, tetracyclines, hydrogen peroxide, and trypsin.
Client information
Emergency Use: Acetylcysteine is most commonly used in emergency, clinically supervised settings to treat life-threatening poisonings (such as Tylenol/acetaminophen ingestion).
- Taste and Odor: The oral liquid formulation has a very strong, unpleasant odor resembling rotten eggs (sulfur) and tastes very bad. Your pet will likely resist taking it. In the hospital, it is often given through a feeding tube or mixed with strong flavorings to ensure the full dose is received.
- Side Effects: The most common side effect is nausea or vomiting. If your pet vomits shortly after receiving an oral dose, contact your veterinarian immediately, as the dose may need to be repeated.
- Monitoring: Your pet will require close monitoring, including frequent blood tests, to ensure the liver is recovering and the toxin is being cleared from the body.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.