Side Effects Seen to Limit Long-Term Use of Apomorphine Infusions in Parkinson’s

Apomorphine infusion, delivered by a portable device, helps to treat Parkinson’s disease and allows reduced use of other medications that may cause symptom fluctuations and treatment side effects. But in the long run, few patients are able to stay on the treatment for more than a few years, an Australian study shows.

The study, “Longterm adherence to apomorphine infusion in patients with Parkinson’s disease: a 10 year observational study,” was recently published in the Internal Medicine Journal.

Researchers at the Royal Adelaide Hospital and the University of Adelaide recruited 36 Parkinson’s patients, who started treatment with apomorphine infusions between 2004 and 2014. The idea was to observe the outcomes and their reasons for quitting the treatment.

None managed to completely stop other medications while taking apomorphine, but 86 percent reduced L-dopa or other treatment doses, with an average reduction of 22.7 percent.

In contrast to L-dopa, which is the precursor of dopamine, apomorphine is a drug that acts by strongly stimulating dopamine receptors. The study showed that among the 20 patients who had taken other dopamine receptor-stimulating drugs before apomorphine, 35 percent could stop these treatments. The rest were able to reduce doses by an average of 40 percent.

The benefits of apomorphine infusions on movement symptoms and quality of life was rated as “much improved or very much improved” by 83 percent of the patients, with the remaining experiencing no change or minimal improvements.

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The 36 patients remained on apomorphine infusion for an average of 21.7 months. Those who continued treatment did so nearly twice as long as the established mean treatment duration — 30.7 months compared to 17.9 months — indicating that patients who quit did so early. By 2016, two-thirds of these patients had stopped the treatment.

To better understand what may have influenced this decision, the research team surveyed patients. It turned out that a majority, 67 percent, had intolerable side effects, and 25 percent did not experience adequate improvement in movement and non-movement symptoms.

One patient reported difficulties in managing the pump, and one died of reasons not related to the therapy during the trial.

Side effects that made people drop the infusion were mainly psychotic symptoms, impulse control disorders, and dopamine dysregulation syndrome — an addiction-like state in which patients tend to use excessive doses of their medications. Since these conditions are linked to excessive dopamine signaling, these side effects are expected. Others also experienced sedation and worsening of dyskinesias (impairment of voluntary movement).

A majority of those who quit continued treatment with other device-assisted approaches, including deep brain stimulation.