Complications and limitations of drug therapy for Parkinson's disease.

Levodopa is the most effective drug treatment for Parkinson's disease (PD). However, its chronic use is associated with dyskinesia, motor fluctuations, and hallucinations. There are various approaches to the management of levodopa complications. Motor fluctuations can be treated with a long-acting levodopa preparation, liquid levodopa, or the addition of dopamine agonists or catechol-O-methyl transferase (COMT) inhibitors. Drugs that may improve levodopa-induced psychiatric complications are olanzapine, clozapine, and ondansetron. A large proportion of patients with long-standing PD cannot be controlled adequately with the available pharmacologic tools and are candidates for surgery. Pallidotomy and deep brain stimulation (DBS) of the globus pallidum pars interna and the subthalamic nucleus are currently the preferred surgical approaches. Appropriate patient selection becomes a critical issue for achieving the best surgical results.