Controversies in the treatment of Parkinson's disease.

Although theoretical reasons exist for believing that selegiline slows the progression of Parkinson's disease, this has not been shown in clinical trials. Selegiline improves the symptoms of Parkinson's disease, allowing the introduction of levodopa to be delayed in de-novo patients and, later, for levodopa to be used at a lower dose. It does not lessen the long-term problems of dyskinesia and fluctuations associated with levodopa therapy. The report of an increased mortality associated with selegiline therapy awaits further evaluation. Of the dopamine agonists, pergolide appears to be more potent than bromocriptine; cabergoline looks promising. The catechol-O-methyltransferase inhibitors, tolcapone and entacopone, prolong the duration of action of levodopa and also show promise. The main objective in the drug treatment of Parkinson's disease remains the optimization of the dose and frequency of levodopa administration.