Its lipophilic structure allows it to cross the blood–brain barrier.Apomorphine possesses affinity for the following receptors (note that a higher Ki indicates a lower affinity):

It has a Ki of over 10,000 nM (and thus negligible affinity) for β-adrenergic, H1, and mACh.Apomorphine has a high clearance rate (3–5 L/kg/hr) and is mainly metabolized and excreted by the liver. It is likely that while the cytochrome P450 system plays a minor role, most of apomorphines metabolism happens via auto-oxidation, O-glucuronidation, O-methylation, N-demethylation, and sulfation. Only 3–4% of the apomorphine is excreted unchanged and into the urine. The half-life is 30–60 minutes, and the effects of the injection last for up to 90 minutes.Toxicity depends on the route of administration; the LD50s in mice were 300 mg/kg for the oral route, 160 mg/kg for intraperitoneal, and 56 mg/kg intravenous. Chemistry
Properties
Apomorphine has a catechol structure similar to that of dopamine. Synthesis
Several techniques exist for the creation of apomorphine from morphine. In the past, morphine had been combined with hydrochloric acid at high temperatures (around 150 °C) to achieve a low yield of apomorphine, ranging anywhere from 0.6% to 46%. More recent techniques create the apomorphine in a similar fashion, by heating it in the presence of any acid that will promote the essential dehydration rearrangement of morphine-type alkaloids, such as phosphoric acid. The method then deviates by including a water scavenger, which is essential to remove the water produced by the reaction that can react with the product and lead to decreased yield.
Dopamine antagonists, by their nature of competing for sites at dopamine receptors, reduce the effectiveness of the agonistic apomorphine.IV administration of apomorphine is highly discouraged, as it can crystallize in the veins and create a blood clot (thrombus) and block a pulmonary artery (pulmonary embolism). Side effects
Nausea and vomiting are common side effects when first beginning therapy with apomorphine; antiemetics such as trimethobenzamide or domperidone, dopamine antagonists, are often used while first starting apomorphine. Around 50% of people grow tolerant enough to apomorphines emetic effects that they can discontinue the antiemetic.Other side effects include orthostatic hypotension and resultant fainting, sleepiness, dizziness, runny nose, sweating, paleness, and flushing. More serious side effects include dyskinesias (especially when taking L-DOPA), fluid accumulation in the limbs (edema), suddenly falling asleep, confusion and hallucinations, increased heart rate and heart palpitations, and persistent erections (priapism). The priapism is caused by apomorphine increasing arterial blood supply to the penis. This side effect has been exploited in studies attempting to treat erectile dysfunction. Pharmacology
Mechanism of action
Apomorphines R-enantiomer is an agonist of both D1 and D2 dopamine receptors, with higher activity at D2. The members of the D2 subfamily, consisting of D2, D3, and D4 receptors, are inhibitory G protein–coupled receptors. The D4 receptor in particular is an important target in the signaling pathway, and is connected to several neurological disorders.