Veterinary Drug Handbook (VDH) is the reference veterinarians turn to when they want an independent source of information on the drugs that are used in veterinary medicine today.

ACETYLCYSTEINE

Chemistry - The N-acetyl derivative of L-cysteine, acetylcysteine occurs as a white, crystallinepowder with a slight acetic odor. It is freely soluble in water or alcohol. Acetylcysteine may also beknown as N-acetylcysteine or N-Acetyl-L-cysteine.

Storage, Stability, Compatibility

When unopened, vials of sodium acetylcysteine should bestored at room temperature (15-30°C). After opening, vials should be kept refrigerated and usedwithin 96 hours.
Acetylcysteine is incompatible with oxidizing agents and solutions can become discolored andliberate hydrogen sulfide when exposed to rubber, copper, iron, and during autoclaving. It does notreact to aluminum, stainless steel, glass or plastic. If the solution becomes light purple in color, potency is not appreciably affected, but it is best to use non-reactive materials when giving the drugvia nebulization. Acetylcysteine solutions are incompatible with amphotericin B, ampicillin sodium, erythromycin lactobionate, tetracycline, oxtetracycline, iodized oil, hydrogen peroxide and trypsin.

Pharmacology - ACETYLCYSTEINE

When administered into the pulmonary tree, acetylcysteine reduces the viscosityof both purulent and nonpurulent secretions and expedites the removal of these secretions viacoughing, suction, or postural drainage. The free sulfhydryl group on the drug is believed to reducedisulfide linkages in mucoproteins. This effect is most pronounced at a pH from 7-9. The drug hasno effect on living tissue or fibrin.
Acetylcysteine also can reduce the extent of liver injury or methemoglobinemia after ingestion ofacetominophen, by providing an alternate substrate for conjugation with the reactive metabolite ofacetominophen, thus maintaining or restoring glutathione levels.

Uses, Indications

Acetylcysteine is used in veterinary medicine as both a mucolytic agent forpulmonary and ophthalmic use and a treatment for acetominophen toxicity in small animals.

Pharmacokinetics - ACETYLCYSTEINE

When given orally, acetylcysteine is absorbed from the GI tract. When administered via nebulization or intratracheally into the pulmonary tract, most of the drug is involvedin the sulfhydryl-disulfide reaction and the remainder is absorbed. Absorbed drug is converted(deacetylated) into cysteine in the liver and then further metabolized.

Contraindications, Precautions, Reproductive Safety

Acetylcysteine is contraindicated (forpulmonary indications) in animals hypersensitive to it. There are no contraindications for its use asan antidote.
Because acetylcysteine may cause bronchospasm in some patients when used in the pulmonarysystem, animals with bronchospastic diseases should be monitored carefully when using this agent.
Reproduction studies in rabbits and rats have not demonstrated any evidence of teratogenic or embryotoxic effects when used in doses up to 17 times normal. It is unknown if acetylcysteineenters milk.

Adverse Effects, Warnings

When given orally for acetominophen toxicity, acetylcysteine cancause GI effects (nausea, vomiting) and rarely, urticaria. Because the taste of the solution is verybad, use of taste masking agents (e.g., colas, juices) have been used. Because oral dosing of thesedrugs may be very difficult in animals, gastric or duodenal tubes may be necessary. When administered into the pulmonary tract, acetylcysteine hypersensitivity has been reportedrarely. Chest tightness, bronchoconstriction, and bronchial or tracheal irritation have also beenreported, but these effects are also considered to occur rarely.

Overdosage, Acute Toxicity

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 listedabove) in most overdose situations.
Drug Interactions, Drug/Laboratory Interactions - The use of activated charcoal as a gut adsorbent of acetominophen is controversial, as charcoal may also adsorb acetylcysteine. In humans, at least 3 hours should pass between giving activated charcoal and the first dose of acetylcysteine.
Because cats can develop methemoglobinemia very rapidly after ingestion of acetominophen, delay in treating with acetylcysteine cannot be recommended.
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