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Acetylcysteine for Dogs, Cats, and Horses

By Barbara Forney, VMD

Commonly prescribed for: Acetaminophen toxicity of dogs and cats; intra-uterine treatment in mares; meconium impaction in foals; adjunct in the treatment of Keratoconjunctivitis Sicca (KCS) and corneal ulcers.

Species: Dogs, Cats, and Horses

Therapeutic Class: Mucolytic


Basic Information

Acetylcysteine is a mucolytic that is used in human medicine to decrease the viscosity of respiratory secretion, particularly in patients with cystic fibrosis. It has a number of uses in veterinary medicine, including the treatment of acetaminophen toxicity of dogs and cats, intra-uterine treatment in mares, meconium impaction in foals, and as an adjunct in the treatment of Keratoconjunctivitis Sicca (KCS) and corneal ulcers.

Acetylcysteine may be administered intravenously or orally in the treatment of acetaminophen poisoning. It may also be nebulized, used topically on the eye, or instilled in the rectum or uterus.

When acetylcysteine is used as a mucolytic in the respiratory tree, GI tract, or uterus, the mechanism of action is through disruption of the disulfide bonds in mucin. This decrease in viscosity of the mucous secretion allows for more efficient clearance. When acetylcysteine is used topically for the treatment of corneal ulceration, the primary mechanism of action is through the inhibition of proteases and collagenases, and the decrease in mucous viscosity. The mechanism of action for the treatment of acetaminophen toxicity is through the provision of additional glutathione substrate.

Dogs and Cats

Acetylcysteine is used to treat acetaminophen toxicity in both dogs and cats. Dogs, and particularly cats, are extremely sensitive to acetaminophen and will develop sever methemoglobinemia and liver damage within hours of ingestion. There is still some debate regarding the exact enzymatic pathway of acetaminophen metabolism in the dog and cat, but it is well established that the hepato-protective qualities of acetylcysteine are due to the provision of additional glutathione precursor. It is critically important to begin therapy as soon as possible, and in cases where a large quantity may have been ingested, some clinicians recommend starting with a loading dose of acetylcysteine.

Horses

Acetylcysteine has a number of clinical uses in the horse. Nebulized acetylcysteine is used for the treatment of meconium and milk aspiration in the neonatal foal. Acetylcysteine retention enemas may be used to treat refractory meconium impactions. It is also used as a mucolytic agent in intra-uterine infusions, and in the treatment of chondroids of the guttural pouch.

Topical Ophthalmic Use

Topical acetylcysteine is used commonly on its own, or in combination with antibiotics or antifungal drugs of the treatment of KCS and corneal ulcers.

Side Effects

  • Oral administration: nausea, vomiting, and hypersensitivity. Oral acetylcysteine tastes terrible. In some cases it is preferable to administer via NG tube.
  • Nebulization: rare side-effects include, hypersensitivity, irritation, bronchoconstriction.

Precautions

  • Acetylcysteine liquid is unstable at room temperature. Ophthalmic solutions are generally kept in the refrigerator and may have a limited shelf life.
  • There are no precautions associated with pregnancy. It is not known if acetylcysteine enters maternal milk.

Drug Interactions

  • Activated charcoal will decrease the absorption of oral acetylcysteine. If possible separate the administration of activated charcoal from the oral administration of acetylcysteine. This may be accomplished by giving the first dose of acetylcysteine intravenously.

Overdose

  • Acetylcysteine has a high margin of safety for overdose. The LD50 in dogs is 1g/kg orally.

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