Parkinson Disease Treated With a Suspected Dopamine Receptor Agonist

A single-blind crossover trial of a putative dopamine receptor stimulating agent, piribedil, was conducted in 16 patients with idiopathic parkinsonism. At maximum dose levels overall improvement in parkinsonian signs averaged 30%. Adverse effects included gastrointestinal disturbances, behavioral alterations, and dyskinesias, but were severe enough to require drug withdrawal in only one patient. The antiparkinsonian efficacy of levodopa together with a peripheral decarboxylase inhibitor, tested in 12 of these patients, was about twice that of piribedil. Levodopa treatment failures due to toxic effects other than dyskinesias responded well to piribedil. As expected of a dopamine receptor agonist, piribedil substantially reduced the central turnover of this monoamine as estimated by the probenecid loading test.