Article Reviews

Apomorphine use in dogs

Bahri LE: Apomorphine. Compendium 28(9):653-657, 2006.

Reviewed by Dr. Lynn Hovda

Reviewers Comments: This article presents a very complete review of the use, dose and route of administration, acute toxicity, and contraindications of apomorphine. The reader is reminded that this product is used in dogs only.

PHARMACOKINETICS: This section provides information on the route of administration, solubility, and metabolism. Oral apomorphine is ineffective as it undergoes first pass metabolism in the liver. The preferred routes are subcutaneous and instillation into the conjunctival sac. Apomorphine is very liphophilic and readily crosses the blood brain barrier. It is metabolized in the liver by oxidation, N-demethylation, sulfation, and glucuronidation and excreted as metabolites in the urine. The time for elimination half-life is 31 minutes.

PHARMACOLOGY: A brief explanation of vomiting centers begins this section. There are two separate centers in the brain: vomiting center and CTZ (chemoreceptive trigger zone). Apomorphine is chemically very close to dopamine and works by stimulating dopamine D2 receptors in the CTZ. It depresses the vomiting center. Emesis in dogs occurs within 3-10 minutes after subcutaneous injection and may occur intermittently for 20-30 minutes. If vomiting does not occur after the initial dose, further doses will not be effective. Other uses of apomorphine are discussed in this section.

INDICATIONS: It is used to induce vomiting in dogs with acute, oral poisoning. A variety of conditions of use and nonuse are discussed in this section.

ACUTE TOXICITY: Prolonged vomiting with acid-base and electrolyte abnormalities can occur even at normal doses. Trimethobenzamide (Tigan™ and others) is the preferred antiemetic as it is a dopamine D2 receptor antagonist. Emetics in the 5-hydroxytryptamine subtype 3 group (alosetron, ondansetron, granisetron, and dolasetoron) are contraindicated as they may result in hypotension. Side effects occurring with excessive doses include respiratory and cardiac depression. Naloxone, levallorphan tartrate or nalorphan can be used to reverse the respiratory depression.

CONTRAINDICATIONS: The use of apomorphine is contraindicated when the dog has ingested an unknown toxin, sharp object, caustic or corrosive substance, petroleum distillate, or central nervous system stimulant or depressant. The use in pregnant dogs is also contraindicated. It should not be used in dogs with known sulfite allergies as it contains sodium metabisulfite as an antioxidant.

DOSAGE AND ADMINISTRATION: Apomorphine should not be used in cats. The subcutaneous (0.1 mg/kg BW) or IV (0.05 mg/kg BW) route can be used in dogs. A third acceptable route is instillation of a portion of a crushed 6 mg tablet into the conjunctival sac. If this method is used, the eye needs to be lavaged well after vomiting has occurred as remaining apomorphine (pH = 3-4) will be irritating to the eye. Intramuscular apomorphine is not as effective as the other routes. Only one dose should be used; subsequent doses are not effective and may be associated with toxicity.

PREPARATIONS: Apomorphine is currently marketed for use in the USA for human beings only. It is not FDA approved for use in animals. It is available through human or compounding pharmacies as a 6mg tablet or capsules containing 3mg or 7mg of apomorphine powder. It is also available as a 10 mg/ml solution for injection in 2 ml ampules.

STORAGE AND HANDLING: The tablets and capsules generally have a shelf life of one year and must be kept in light resistance containers at room temperature. Exposure to light causes the product to oxidize and turn green. Discolored tablets and solutions should not be used.