Trial Evaluating the Efficacy of Pimavanserin, a Selective Serotonin 5-HydroxyTryptamine-2A (5HT2A) Inverse Agonist, to Treat Impulse Control Disorders in Parkinson's Disease.

There is no consensus on the treatment of Impulse Control Disorder (ICD) in Parkinson Disease (PD) though it is recommended to reduce the dosage of dopamine agonists (DA). Reduction of DA frequently leads to a worsening of motor signs (parkinsonism or dyskinesias due to the concomitant increase of levodopa doses) and non-motor signs with the appearance of a DA withdrawal syndrome (DAWS). Chronic stimulation of the sub-thalamic nuclei may reduce ICD but is restricted to a minority of patients and cases of new-onset ICD symptoms post stimulation have been reported. The benefit of amantadine in pathological gambling is controversial and the efficacy of clozapine has been reported in a few cases but with serious safety limitations. Very recently, naltrexone did not significantly improve ICD. Thus, an efficacious and safe treatment of ICD in PD remains an unmet need for clinical practice. Recently, it has been reported that pimavanserin, a selective serotonin 5-HT2A inverse agonist with a satisfactory safety profile without motor side effects, was efficient in improving psychosis, insomnia and day-time sleep in PD. Pimavanserin, marketed under the tradename NUPLAZID® was approved in 2016 by the U.S. Food and Drug Administration (FDA) for the treatment of hallucinations and delusions associated with Parkinson's disease psychosis. The link between serotonin and ICD has been well established, since the enhancement of 5HT2A receptors stimulation is associated to ICD, since serotonin modulates mesolimbic dopaminergic reward system transmission and given that serotonin neurotransmission is increased during chronic intake of dopamine agonist such as pramipexole which is well-known to induce ICD in PD patients. Thus, there is a large body of evidence suggesting that the decrease of the 5HT2A activity could be efficient in reducing ICD in PD. This further supports the concept of testing the efficacy of pimavanserin (a selective 5HT2A inverse agonist) for treating ICD in PD.