Mucomist

Acetylcysteine is used in veterinary medicine as both a mucolytic agent in the pulmonary tree and as a treatment for acetaminophen, xylitol, or phenol toxicity in small animals. Acetylcysteine is used investigatively as an antiinflammatory for chronic upper respiratory disease in cats, as an adjunct in heavy metal removal, and topically in the eye to halt the melting effect of collagenases and proteinases on the cornea.
It has been used anecdotally with aminocaproic acid to treat degenerative myelopathy in dogs, but data is lacking showing efficacy.
In horses with strangles, acetylcysteine instilled into the gutteral pouch has been used to help break up chondroids and avoid the need for surgical removal. Acetylcysteine enemas have been used in neonatal foals to break up meconium refractory to repeated enemas.

Acetylcysteine is contraindicated (for pulmonary indications) in animals hypersensitive to it. There are no contraindications for its use as an antidote.
Because acetylcysteine may cause bronchospasm in some patients when used in the pulmonary system, animals with bronchospastic diseases should be monitored carefully when using this agent.

When administered into the pulmonary tree, acetylcysteine reduces the viscosity of both purulent and nonpurulent secretions and expedites the removal of these secretions via coughing, suction, or postural drainage. The free sulfhydryl group on the drug is believed to reduce disulfide linkages in mucoproteins; this effect is most pronounced at a pH from 7–9. The drug has no effect on living tissue or fibrin.
Acetylcysteine can reduce the extent of liver injury or methemoglobinemia after ingestion of acetaminophen or phenol, by providing an alternate substrate for conjugation with the reactive metabolite of acetaminophen, thus maintaining or restoring glutathione levels.

ACTIVATED CHARCOAL: The use of activated charcoal as a gut adsorbent of acetaminophen is controversial, as charcoal may also adsorb acetylcysteine. Because cats can develop methemoglobinemia very rapidly after ingestion of acetaminophen, do not delay acetylcysteine treatment and preferably give the first dose intravenously. If using the solution (not labeled for injectable use), it is preferable to use a 0.2 micron in-line filter.

When given orally for acetaminophen toxicity, acetylcysteine can cause GI effects (nausea, vomiting) and rarely, urticaria. Because the taste of the solution is very bad, taste-masking agents (e.g., colas, juices) have been used. Since oral dosing of these drugs may be very difficult in animals, gastric or duodenal tubes may be necessary.
Intravenous administration appears to be very well tolerated in veterinary patients. IV boluses in humans have caused changes in blood pressure (hyper-, hypo-tension), GI effects and allergic reactions.
Rare adverse effects reported when acetylcysteine is administered into the pulmonary tract, include: hypersensitivity, chest tightness, bronchoconstriction, and bronchial or tracheal irritation.

The LD50 of acetylcysteine in dogs is 1 g/kg (PO) and 700 mg/kg (IV). It is believed that acetylcysteine is quite safe (with the exception of the adverse effects listed above) in most overdose situations.

Monitoring:

When used for acetaminophen poisoning:

• Hepatic enzymes (particularly in dogs)
• Acetaminophen level, if available (particularly in dogs)
• Hemogram, with methemoglobin value (particularly in cats)
• Serum electrolytes, hydration status

If only a portion of the solution is used, store the remainder in a refrigerator and use only for inhalation within 96 hours. Store in a cool. Protect from light.