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Apomorphine Maleate for Veterinary Use
by Barbara Forney, VMD
Apomorphine is a D2-dopamine-receptor agonist that works at the level of the chemoreceptor trigger zone (CRTZ) of the brain in dogs. Emesis is regulated by both neural pathways and by humoral pathways within the brain. Most emetic and antiemetic drugs work through the humoral pathways on the CRTZ. There are species differences for both emetic and antiemetic drugs based on receptor differences in the CRTZ. Cats do not respond consistently to apomorphine and its use is controversial in this species.
Emetics are an important early treatment for some orally ingested toxins. Emetics generally remove only 40-60% of the stomach contents and are useful in the first four hours after ingestion. Apomorphine is metabolized in the liver and excreted in urine.
Apomorphine is the emetic of choice in dogs. It commonly is given parenterally (IM or IV) or topically in the conjunctival sac. When given intravenously, vomiting occurs rapidly. After intramuscular injection, vomiting should occur within five minutes. Conjunctival administration usually is effective although not as quickly or reliably as parenteral administration. If vomiting does not occur after one dose, repeated doses are unlikely to be effective and increase the likelihood of undesirable side-effects or toxicity. Apomorphine is poorly absorbed orally.
Apomorphine Maleate Side Effects
- In addition to vomiting, apomorphine can cause either CNS stimulation or depression. CNS stimulation is a more common side effect. Naloxone may be used to reverse CNS and respiratory signs, but will not diminish the vomiting.
- Prolonged vomiting may occur. After ophthalmic treatment, rinsing the conjunctival sac with saline may decrease residual drug absorption.
Emetics including apomorphine should not be used in patients with increased risk of aspiration such as hypoxia, dyspnea, those in shock, seizuring, comatose or with deteriorating CNS function.
Emetics including apomorphine should not be used to treat ingestion of caustics, including strong acids or alkali. This is due to increased injury from re-exposure of the esophagus and gastric mucosa.
The use of emetics after ingestion of CNS stimulants such as strychnine may precipitate seizures.
Petroleum distillates ingestion carries an increased risk of aspiration when emetics are used. Clinical judgment should be exercised regarding the risk of aspiration weighed against the risk of toxicity.
Apomorphine should not be used in animals with decreased liver function.
Apomorphine should not be used in rabbits or rodents. These species lack either the ability to vomit or do not have strong enough abdominal musculature.
- Apomorphine should not be used to treat ingestion of CNS-depressant drugs such as opiates or barbiturates.
- Apomorphine should not be used in animals that are known to be hypersensitive to morphine and related drugs.
- Antiemetic drugs such as phenothiazines may decrease the effectiveness of apomorphine.
Overdose with apomorphine can cause respiratory and cardiac depression, CNS stimulation or depression and protracted vomiting. Naloxone may be used to reverse CNS and respiratory signs, but will not diminish the vomiting.
About the Author
Dr. Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania. She has a master's degree in animal science from the University of Delaware and graduated from the University of Pennsylvania School of Veterinary Medicine in 1982.
She began to develop her interest in client education and medical writing in 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.
Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.
You can purchase books by Dr. Forney at www.exclusivelyequine.com
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