Apomorphine

Apomorphine is a type of dopaminergic agonist, a morphine derivative. Apomorphine is a relatively non-selective dopamine receptor agonist, having possible slightly higher affinity for D2-like dopamine receptors.

Historically, apomorphine has been tried for a variety of uses including psychiatric treatment of homosexuality in the early 20th century. Currently, apomorphine is used in the treatment of Parkinson's disease and erectile dysfunction. It was also successfully used in the treatment of heroin addiction, a purpose for which it was championed by the author William S. Burroughs. It is a potent emetic, meaning that it should not be administered without an antiemetic such as domperidone. The emetic properties of apomorphine are exploited in veterinary medicine to induce therapeutic emesis in canines that have recently ingested toxic or foreign substances.

For treatment of erectile dysfunction, it is believed that dopamine receptors in the hypothalamic region of the brain are the main target, as although dopamine receptors in the penis do facilitate erection, they do so far more weakly than those in the brain.

Apomorphine is clear as a liquid but stains green. Therefore care must be taken to avoid splashes. Apormophine does not remain stable for more than 24 hours in a plastic container, so glass syringes are used.

Use in Parkinson's disease
First mooted as a treatment for Parkinson's disease as early as 1951, its clinical use was first reported in 1970 by Cotzias et al, although its emetic properties and short half-life made oral use impractical. A later study found that combining the drug with the antiemetic domperidone, improved results significantly.

Therapeutic use in Parkinson's disease is effective because of the drugs strong dopaminergic action, with a rapid effect (within 3-20 minutes of injection) but a brief duration. Whilst apomorphine can be used in combination with l-dopa, the intention is usually to wean patients off of this, as by this stage they will probably be experiencing a great deal of tardive dyskinesias and "off" periods. Following a successful apomorphine challenge, training of patient and caregiver, and careful dose titration, there is no reason why an apomorphine pump can not be an effective monotherapy.