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The most commonly used antiviral drug is amantadine (Symmetrel) which reduces symptoms of Parkinson's disease by blocking the reuptake of dopamine resulting in an increase in the availability of dopamine in the brain. After several months, the effectiveness wears off in approximately one third to one half of the patients. Amantadine is most useful to treat levodopa-induced dyskinesia. Amantadine is considered as only moderately effective resulting in its being prescribed more as an add-on medication rather than as a monotherapy.

Side effects include significant cognitive impairment (e.g., hallucinations) and for this reason, antiviral drugs are usually not given to older people or to people who already experience cognitive symptoms. Other side effects include:

• Blurred vision
• Depression
• Edema
• Confusion

Other Medications for Parkinson's Disease

There are several other medications that have not been approved by the Food and Drug Administration for treatment of Parkinson's disease symptoms but may be used to help control various symptoms. For example, botulinum toxin injections may be administered to reduce saliva production and drooling. Collagen injections may help voice and speech disorders by augmenting the vocal fold.

Neuroleptic Malignant Syndrome

Neuroleptic Malignant Syndrome (NMS) is a rare complication of Parkinson's disease and is usually triggered by a reduction or discontinuation of antiparkinsonian drugs, especially, but not exclusively, levodopa. Additional triggers for NMS are infection and dehydration. Symptoms include high fever, increased rigidity and exacerbation of Parkinson's disease symptoms, disturbances of consciousness, disturbances of the autonomic system (including blood pressure), and elevated creatine kinase levels in the blood.

It is critical for Neuroleptic Malignant Syndrome to be treated immediately as it can lead to pneumonia or renal failure. Treatment usually includes infusion of intravenous fluids, cooling to bring down fever, increasing or reintroducing antiparkinsonian medication, as well as administration of other drugs such as bromocriptine and dantrolene. There is ongoing research into the efficacy of other medications in treating NMS.

Effective Use of Parkinson's Disease Drugs

According to a Practice Parameter published by the American Academy of Neurology in 2002, the conclusions regarding initial treatment for Parkinson's disease include the following:

• First-line treatment of newly symptomatic Parkinson's disease patients should consist of either levodopa or dopamine agonists. Levodopa is more effective for symptomatic relief but carries greater risks for dyskinesia.
• Sustained release levodopa provides no advantage over the immediate release form of the drug.
• Selegiline, while of limited symptomatic benefit, has no neuroprotective properties.

In 2006, the Food and Drug Administration approved rasagiline as a monotherapy for treatment of early Parkinson's disease and as add-on therapy to levodopa for moderate and advanced stages.

The American Academy of Neurology published an additional Practice Parameter for the treatment of Parkinson's disease in which the following conclusions were drawn:

• Entacapone and rasagiline should be offered to reduce "off" time
• Amantadine may be considered to reduce dyskinesia
• Deep brain stimulation of the subthalamic nucleus may be considered to improve motor function, and reduce "off" time, dyskinesia, and medication usage.