Ropinirole binds the dopamine receptors D3 and D2. Although the precise mechanism of action of ropinirole as a treatment for Parkinson's disease is unknown, it is believed to be related to its ability to stimulate these receptors in the striatum. This conclusion is supported by electrophysiologic studies in animals that have demonstrated that ropinirole influences striatal neuronal firing rates via activation of dopamine receptors in the striatum and the substantia nigra, the site of neurons that send projections to the striatum.
Ropinirole is a nonergot dopamine agonist with high relative in vitro specificity and full intrinsic activity at the D2 subfamily of dopamine receptors, binding with higher affinity to D3 than to D2 or D4 receptor subtypes. The relevance of D3 receptor binding in Parkinson's disease is unknown. The mechanism of ropinirole-induced postural hypotension is presumed to be due to a D2 -mediated blunting of the noradrenergic response to standing and subsequent decrease in peripheral vascular resistance.
Hepatic. Ropinirole is extensively metabolized to inactive metabolites via N -despropylation and hydroxylation pathways, largely by the P450 isoenzyme CYP1A2. N-despropyl ropinirole is the predominant metabolite found in urine (40%), followed by the carboxylic acid metabolite (10%), and the glucuronide of the hydroxy metabolite (10%).
Symptoms of overdose include agitation, chest pain, confusion, drowsiness, facial muscle movements, grogginess, increased jerkiness of movement, symptoms of low blood pressure (dizziness, light-headedness)upon standing, nausea, and vomiting.
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