Parkinson's disease (PD) is a
neurodegenerative disorder that affects an estimated 1 million people in the US and
tens of millions worldwide. Medication
therapy has made significant advances and improvements especially over the last 10 years. A number of new treatments and new strategies have emerged and the quality of life for the average sufferer has improved. This review will describe the rationale and strategies for current medical
therapies in PD, with special emphasis on the use of
antipsychotic agents.
Levodopa remains the most efficacious medication for the management of PD. Long-term use of
levodopa, however, is associated with the development of motor fluctuations including
dyskinesia. Trials with
dopamine agonists have demonstrated a delay in the onset of
dyskinesia with the use of this
therapy. There is also active, ongoing investigation to determine whether a
neuroprotective effect may be present with agonist
therapy.
Anticholinergics have been successfully used to treat
tremor as well as sialorrhoea and urinary urgency.
Catechol-O-methyltransferase inhibitors increase 'on time', decrease 'off time,' and improve motor scores. Continuous stimulation of
dopamine receptors may decrease the fluctations observed with pulsatile delivery of anti-Parkinsonian medications, but this will require more study.
Monoamine oxidase-B inhibitors, specifically
selegiline, may provide symptomatic improvement; the question as to whether a neuroprotective benefit is present remains unanswered.
Amantadine has demonstrated both symptomatic benefit and
dyskinesia benefit in some patients. Selective
dopamine blockers such as
clozaril and
quetiapine, have been shown to be effective in the treatment of
psychosis. This class of medications is particularly useful as an adjunctive to
levodopa and
dopamine agonists. Doses of
dopaminergic drugs can be escalated to treat Parkinsonian symptoms, whereas selective
dopamine blockers can be added to block
psychosis. Old management strategies required a reduction in dopaminergic
therapy and therefore worsened Parkinsonian symptoms. Even though there have been great advances in the medical options for symptomatic management of PD, there are still many unmet needs for this patient population.