Piribedil

Piribedil (trade names Trivastal, Pronoran, Trastal, Trivastan) is an antiparkinsonian agent and piperazine derivative which acts as a D2 and D3 receptor agonist. It also has α2-adrenergic antagonist properties.

Indications

 * Treatment of Parkinson's disease (PD), either as monotherapy (without L-DOPA (Levodopa)) or in combination with L-DOPA therapy, in the early stages as well as in the advanced stages of the disease.
 * Treatment of pathological cognitive deficits in the elderly (impaired attention, motivation, memory, etc.).
 * Treatment of dizziness in the elderly.
 * Treatment of retinal ischemic manifestations.
 * Adjuvant treatment in intermittent claudication due to peripheral vascular disease (PVD) of the lower limbs (stage 2).
 * Anhedonia and treatment-resistant depression in unipolar and bipolar depressives (off label).
 * Treatment of gait disorders associated to Parkinson disease (no related cause) and other forms of parkinsonism

Other uses
The drug has been shown to enhance working memory capacities in normal aging adults.

In age-related memory impairment, it has a positive effect on psychophysiological state of elderly people, improving memory and attention and increasing the velocity of psychomotor reactions and lability of nervous processes.

It enhances cognitive skill learning in healthy older adults.

It showed a positive effect in restless legs syndrome

Parkinson's disease
Administration of piribedil should be initiated with one tablet daily during the first week. Dosage should then be gradually increased every week until achieving the optimal therapeutic dose:
 * as monotherapy: three to five tablets in three to five doses daily.
 * in combination with L-dopa therapy: one to three tablets daily.

Other indications
One tablet daily at the end of the main meal. In severe cases: two tablets daily in two doses.

Adverse effects

 * Minor gastrointestinal upset (nausea, vomiting, flatulence, etc.) in predisposed individuals, or when taken between meals: adjust dosage individually, and/or add domperidone (Motilium).
 * Orthostatic hypotension or drowsiness may occur, particularly in predisposed individuals (underlying condition or causative illness).

Interactions
Dopamine antagonists reduce the effect of piribedil.

Overdose
At very high doses, piribedil has an emetic action on the chemoreceptor trigger zone (CTZ). Tablets will thus be rapidly rejected, which explains why no data are currently available concerning the risk of overdosage.

Receptor affinities

 * Dopamine receptor agonist, selective for subtypes D2 and D3.
 * Adrenergic receptor antagonist, subtypes α2a and α2c: could be the reason why piribedil seems to cause less drowsiness than other dopamine agonists.
 * Lack of affinity to serotonin receptor 5-HT2B: theoretically no risk of heart valve impairment.