Apomorphine is an agonist of D1 and D2 receptors in the central nervous system. It is capable of activating a receptor to induce a full or partial pharmacological response. The compound is historically a morphine decomposition product made by boiling morphine with concentrated acid, hence the -morphine suffix.
Contrary to its name, apomorphine does not actually contain morphine or its skeleton, nor does it bind to opioid receptors. Apomorphine is now recognized as the oldest antiparkinsonian drug on the market.
Though still underused, it is increasingly prescribed in Europe for patients with advanced Parkinson’s disease (PD) with motor fluctuations. In 1845, in Finland, Arppe made the first synthesis of apomorphine (morphine + sulfuric acid).
In 1869, Gee in England discovered emetic (vomiting), stereotypogenic, sedative, and excitatory properties by doing experiments on dogs and humans. The same year Hare in England found it useful in the treatment of alcoholism. In 1884, Weill in France suggested Apomorphine as a treatment for several motor disorders: chorea, shaking, and Parkinson’s disease. In 1979, Corsini in Italy discovered that the combination of apomorphine and domperidone prevents nausea, drowsiness, sedation, and arterial hypotension. In 2004, the FDA approved Apokyn® (Apomorphine) as a rescue therapy for Parkinson’s disease to treat episodes of hypomobility. Apomorphine is one of the most effective medications that can induce vomiting in dogs. As with all vomiting medications, usually, only 40 to 60 percent of the stomach’s contents are removed.
The drug is slowly absorbed after oral ingestion so it is usually given as an injection or topical on the eye. When given intravenously, vomiting occurs rapidly. After intramuscular injection, vomiting usually occurs within 5 minutes but may be more prolonged. Topical administration of apomorphine to the conjunctival sac of the eye is usually effective but is less reliable than injectable.
Apomorphine is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.
This drug is not approved for use in animals by the Food and Drug Administration but it is prescribed legally by veterinarians as an extra-label drug.
Apomorphine is primarily available through compounding pharmacies. Apomorphine should not be used in animals with known hypersensitivity, breathing difficulty, seizing, physically weak, or comatose. Vomiting should not be induced if the animal has already vomited several times or has ingested acid, caustic agents or petroleum distillates. If vomiting does not occur within the expected time, additional doses will likely not result in vomiting and may result in toxicity. Apomorphine may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with apomorphine.
Such drugs include prochlorperazine, chlorpromazine, or certain narcotics. Apomorphine can cause nervous system depression or stimulation but tends to cause more stimulatory effects. In dogs, apomorphine is dosed at 0.015 mg per pound (0.03 mg/kg) IV or 0.02 mg per pound (0.04 mg/kg) IM (IV route is preferred). The use of apomorphine in cats is controversial but can be given at a dose of 0.02 mg per pound (0.04 mg/kg) IV or 0.04 mg per pound (0.08 mg/kg) IM or SQ.
If not injected, a portion of the tablet may be crushed in a syringe and dissolved with a few drops of water, and administered into the conjunctival sac, approximately 1 tablet per 50 pounds. After sufficient vomiting occurs, rinse the conjunctival sac to remove residual apomorphine.
- Opioid receptors are a group of inhibitory G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins, and nociceptins. The opioid receptors are ~40% identical to somatostatin receptors (SSTRs). Opioid receptors are distributed widely in the brain, in the spinal cord, on peripheral neurons, and digestive tract. [Back]