Parkinson's disease (PD) is a common
neurodegenerative disease. While its cause remains elusive, much progress has been made regarding its treatment. Available drugs have a good symptomatic effect, but none has yet been shown to slow the progression of the disease in humans. The most efficacious
drug is
levodopa, but it remains unclear whether the symptomatic benefit is associated with neurotoxic effects and long-term deterioration. The long-term problem associated with
levodopa is the appearance of
dyskinesias, which is significantly delayed among patients treated with
dopamine agonists as initial
therapy. Less clear is the role of other drugs in PD, such as
monoamine oxidase inhibitors (MAOIs), including
selegiline and
rasagiline, the putative N-meihyl-o-aspartaie (
NMDA) receptor antagonists
amantadine and
memantine, and the
muscarinic receptor blockers. All these may be used as initial
therapy and delay the use of
dopaminergic drugs, or can be added later to reduce specific symptoms (
tremor or
dyskinesias). Advanced PD is frequently associated with
cognitive decline. To some extent, this can be helped by treatment with
cholinesterase inhibitors such as
rivastigmine. Similarly,
hallucinations and delusions affect PD patients in the advanced stages of their disease. The use of classical
neuroleptic drugs in these patients is contraindicated because of their extrapyramidal effects, but atypical drugs, and particularly
clozapine, are very helpful. The big void in the
therapy of PD lies in the more advanced stages. Several motor symptoms, like postural instability,
dysphagia, and
dysphonia, as well as
dyskinesias, are poorly controlled by existing drugs. New
therapies should also be developed against autonomic symptoms, particularly
constipation.