Acetylcysteine

Mucolytic Agent; Antidote Thiol-containing compound; N-acetyl derivative of cysteine

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO Acetaminophen toxicity: 140 mg/kg loading dose, then 70 mg/kg q6h for 7 treatments; Mucolytic: 50-100 mg/kg q8-12h q6h for toxicity; q8-12h for mucolytic Duration: For toxicity: 7 treatments; for mucolytic: as needed
Notes: Administer with food to reduce GI upset. For acetaminophen toxicity, initiate as soon as possible.
Dog IV Acetaminophen toxicity: 140 mg/kg loading dose, then 70 mg/kg q6h for 7 treatments q6h Duration: 7 treatments
Notes: Dilute in 5% dextrose or saline and administer slowly over 15-30 minutes. Monitor for anaphylactoid reactions.
Cat PO Acetaminophen toxicity: 140 mg/kg loading dose, then 70 mg/kg q6h for 7 treatments q6h Duration: 7 treatments
Notes: Cats are highly sensitive to acetaminophen; NAC is critical. Administer with food.
Cat IV Acetaminophen toxicity: 140 mg/kg loading dose, then 70 mg/kg q6h for 7 treatments q6h Duration: 7 treatments
Notes: Dilute and administer slowly. Monitor for vomiting and hypotension.
Horse PO Mucolytic: 10-20 mg/kg q12h q12h Duration: 5-7 days or as needed
Notes: May be administered via nasogastric tube if needed.
Horse IV Antioxidant support: 5-10 mg/kg q24h q24h Duration: Variable
Notes: Use cautiously; rapid IV administration may cause hypotension.
Cattle PO Mucolytic: 50-100 mg/kg q12h q12h Duration: 3-5 days
Notes: Off-label; ensure adequate hydration.
Cattle IV Acetaminophen toxicity: 140 mg/kg loading dose, then 70 mg/kg q6h q6h Duration: 7 treatments
Notes: Rarely needed; use with caution.
Small Ruminants PO Mucolytic: 50-100 mg/kg q12h q12h Duration: 3-5 days
Notes: Off-label; monitor for GI upset.
Rabbit PO Mucolytic: 50-100 mg/kg q12h q12h Duration: As needed
Notes: Off-label; use with caution in rabbits due to GI stasis risk.
Bird/Poultry PO Mucolytic: 50-100 mg/kg q12h q12h Duration: As needed
Notes: Off-label; ensure adequate hydration.
Exotic/Other PO Mucolytic: 50-100 mg/kg q12h q12h Duration: As needed
Notes: Off-label; species-specific dosing may vary.

Clinical Indications & Species Uses

General Indications
  • Mucolytic agent for conditions with excessive or thick mucus
  • Antidote for acetaminophen toxicity
  • Antioxidant and glutathione precursor
Dog (Canine)
  • Mucolytic therapy for respiratory conditions with thick mucus (e.g., bronchitis, pneumonia)
  • Antidote for acetaminophen (paracetamol) toxicity
  • Adjunctive therapy for hepatoprotection in various liver diseases (off-label)
  • Treatment of keratoconjunctivitis sicca (KCS) when used topically (off-label)
Cat (Feline)
  • Antidote for acetaminophen (paracetamol) toxicity
  • Mucolytic therapy for respiratory conditions (less common)
  • Adjunctive therapy for hepatic support (off-label)
Horse (Equine)
  • Mucolytic therapy for respiratory diseases (e.g., chronic obstructive pulmonary disease, recurrent airway obstruction)
  • Antioxidant support in exertional myopathy (off-label)
Cattle (Bovine)
  • Mucolytic therapy for respiratory disease (e.g., pneumonia, shipping fever) as adjunctive treatment
  • Antidote for acetaminophen toxicity (rarely used)
Small Ruminants (Sheep / Goat)
  • Mucolytic therapy for respiratory disease (off-label)
  • Antidote for acetaminophen toxicity (rarely used)
Rabbit & Small Mammals
  • Mucolytic therapy for respiratory disease (off-label)
  • Antidote for acetaminophen toxicity (off-label)
Avian & Poultry
  • Mucolytic therapy for respiratory disease (off-label)
  • Antidote for acetaminophen toxicity (off-label)
Exotic & Other Species
  • Mucolytic therapy for respiratory disease in small mammals and reptiles (off-label)
  • Antidote for acetaminophen toxicity in various species (off-label)

Pharmacology & Mechanism of Action

Drug Class: Mucolytic Agent; Antidote | Pharmacological Group: Thiol-containing compound; N-acetyl derivative of cysteine

Mechanism of Action: Acetylcysteine (N-acetyl-L-cysteine, NAC) exerts its mucolytic action by breaking disulfide bonds in mucoproteins, reducing mucus viscosity and elasticity. As an antidote for acetaminophen toxicity, NAC acts as a precursor for glutathione synthesis, replenishing hepatic glutathione stores and facilitating the detoxification of the reactive metabolite N-acetyl-p-benzoquinone imine (NAPQI). It also possesses antioxidant properties, scavenging free radicals and reducing oxidative stress.

Pharmacodynamics: Acetylcysteine reduces mucus viscosity in respiratory conditions, improving clearance. In acetaminophen toxicity, it prevents hepatic necrosis by restoring glutathione. It also has anti-inflammatory and antioxidant effects, which may be beneficial in various conditions. The onset of mucolytic action is rapid after inhalation, while systemic effects depend on glutathione replenishment.

⚑ Pharmacokinetics Summary

Absorption: After oral administration, acetylcysteine is well absorbed from the gastrointestinal tract, but undergoes extensive first-pass metabolism in the liver, resulting in low bioavailability. After inhalation, it acts locally with minimal systemic absorption. Intravenous administration provides immediate systemic availability.
Distribution: Acetylcysteine is widely distributed in body tissues and fluids. It crosses the placenta and is distributed into milk. It is primarily found in extracellular fluid and penetrates cells where it is converted to cysteine and glutathione.
Metabolism: Acetylcysteine is rapidly deacetylated in the liver and intestinal wall to cysteine, which is then incorporated into glutathione. It also undergoes oxidation to various disulfides. The metabolism is extensive and rapid.
Excretion: Metabolites are excreted primarily in the urine as inorganic sulfates, taurine, and unchanged drug in small amounts. Fecal excretion is minimal. The elimination half-life is short, approximately 2-6 hours depending on species.
Half-Life: Dogs: ~2-3 hours; Cats: ~2-4 hours; Horses: ~1.5-2 hours; Humans: ~5.6 hours (for reference)
Bioavailability: Oral bioavailability is low (approximately 10-20%) due to extensive first-pass metabolism. Inhalation provides local delivery with minimal systemic absorption.
Protein Binding: Acetylcysteine is moderately protein-bound (approximately 50-80%) in plasma, mainly to albumin.

Available Formulations & Strengths

Oral Solution 10% (100 mg/mL), 20% (200 mg/mL) (PO)
Oral Tablet 600 mg, 1000 mg (PO)
Injectable Solution 10% (100 mg/mL), 20% (200 mg/mL) (IV)
Nebulizer Solution 10% (100 mg/mL), 20% (200 mg/mL) (Inhalation)
Ophthalmic Solution 5% (50 mg/mL) (Ophthalmic)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to acetylcysteine or any component
  • Peptic ulcer disease (oral use may exacerbate)
  • Severe hepatic impairment (unless treating acetaminophen toxicity)
  • Asthma or bronchospasm (inhalation may trigger)
  • Concurrent use with activated charcoal (may reduce absorption of NAC)
Warnings & Clinical Precautions:
  • Use with caution in animals with a history of bronchospasm or asthma; inhalation may cause bronchoconstriction.
  • Rapid IV administration may cause anaphylactoid reactions (flushing, hypotension, bronchospasm); administer slowly.
  • Oral administration may cause vomiting; administer with food or via feeding tube if necessary.
  • In cats, acetaminophen toxicity is life-threatening; NAC should be given promptly and aggressively.
  • Use in pregnant or lactating animals only when clearly needed; safety not fully established.
  • In food animals, observe withdrawal times; extra-label use requires veterinary oversight.
  • NAC may interfere with laboratory tests (e.g., serum ketone bodies, lactate dehydrogenase).

Adverse Effects & Reactions

Common:

  • Vomiting
  • Nausea
  • Diarrhea
  • Anorexia
  • Injection site reactions (IV)
  • Cough or bronchospasm (inhalation)

Serious / Severe:

  • Anaphylactoid reactions (IV rapid administration)
  • Severe bronchospasm
  • Hypotension
  • Angioedema
  • Seizures (rare)

Rare:

  • Hepatotoxicity (paradoxical)
  • Renal impairment
  • Thrombocytopenia
  • Allergic dermatitis

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Activated charcoal May adsorb acetylcysteine, reducing its absorption and efficacy; separate administration by at least 2 hours. Moderate
Nitroglycerin Acetylcysteine may potentiate the vasodilatory effects of nitroglycerin, leading to hypotension. Moderate
Carbamazepine Acetylcysteine may reduce carbamazepine levels. Mild
Chloramphenicol Acetylcysteine may reduce the efficacy of chloramphenicol by interfering with its uptake. Mild
Cisplatin Acetylcysteine may reduce the nephrotoxicity of cisplatin but may also reduce its antitumor efficacy. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Vomiting
  • Diarrhea
  • Hypotension
  • Tachycardia
  • Bronchospasm
  • Metabolic acidosis
  • Seizures (in severe cases)

Emergency Treatment Protocol: Treatment is symptomatic and supportive. For oral overdose, induce emesis if within 1-2 hours and administer activated charcoal (if not contraindicated). Monitor vital signs, respiratory function, and electrolyte balance. For severe reactions, administer antihistamines, corticosteroids, and epinephrine as needed. IV fluids may be required for hypotension. In cases of anaphylactoid reactions, discontinue infusion and treat aggressively.

Food Animal Withdrawal Times

πŸ₯© Meat: 0 daysπŸ₯› Milk: 0 daysπŸ₯š Eggs: 0 days

Acetylcysteine is not approved for food animals; withdrawal times are not established. When used extra-label, consult a veterinarian and follow FARAD guidelines. A conservative withdrawal time of at least 24 hours for meat and milk is often recommended, but official withdrawal times are not defined.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 15-30Β°C (59-86Β°F).

Light Sensitivity: Light-sensitive β€” protect from direct exposure.

Handling & Special Conditions: Protect from light and moisture. Keep container tightly closed. Do not freeze. Opened solutions should be used within 24 hours if refrigerated; discard unused portions.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; approved for human use as a mucolytic and antidote.

Extra-Label (Off-Label) Use: In the US, acetylcysteine is not FDA-approved for veterinary species; use in animals is extra-label. Under AMDUCA, extra-label use is permitted by or on the order of a veterinarian within a valid VCPR, provided withdrawal times are observed for food animals.

Clinical Pearls & Practice Notes

πŸ’‘ Clinical Insights: Acetylcysteine is a versatile drug in veterinary medicine, primarily used as a mucolytic and as an antidote for acetaminophen toxicity, especially in cats and dogs. In cats, acetaminophen toxicity is a medical emergency; NAC should be administered as soon as possible, ideally within 8 hours of ingestion. The oral route is preferred for toxicity, but IV administration is used when oral is not feasible. For mucolytic therapy, inhalation is often used in horses and small animals, but systemic administration may be beneficial. NAC has antioxidant properties that may be useful in various conditions, but evidence is limited. Always monitor for adverse effects, especially during IV administration. In food animals, extra-label use requires careful consideration of withdrawal times. Consult a veterinary clinical pharmacist or toxicologist for specific dosing and management.

References & Literature

  • πŸ“š Plumb's Veterinary Drug Handbook
  • πŸ“š Papich Veterinary Pharmacology and Therapeutics
  • πŸ“š Compendium of Veterinary Products (CVP)