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Since the underlying disease process of Parkinson's disease involves the death of dopamine-producing cells and the subsequent reduction of dopamine available in the brain, the objective of treatment is to increase the amount of dopamine by using agents that either:

• Increase dopamine levels in the brain
• Stimulate dopamine receptors in the brain
• Slow the metabolism and breakdown of dopamine in the brain and reduce the fluctuations of dopamine in the blood

To meet these objectives, there are three categories of medication used to treat Parkinson's disease, namely:

• Levodopa - increases levels of production of dopamine
• Dopamine agonists - stimulate the dopamine receptors by mimicking the effects of dopamine in the brain and cause the neurons to behave as if there was enough dopamine present
• MAO-B and COMT inhibitors - slow the metabolism of dopamine in the body and keep levels of dopamine in the blood at more constant levels

In addition to the dopamine-related drugs, two other classes of drugs may be prescribed to reduce some symptoms of Parkinson's disease, namely anticholinergic drugs and antiviral drugs. They are only mildly to moderately effective and are used only in combination with other medication.

Medical management of Parkinson's disease consists medication given either alone (monotherapy) or in combinations. There is considerable debate regarding which drugs to start first, when to combine drugs, and in what order. Regardless of which medication is chosen for treatment, the dose is initiated at the lowest level possible and then slowly increased until symptom relief is achieved and side effects are tolerable.

The American Academy of Neurology and the Movement Disorder Society both concur that levodopa is the most effective drug for treatment of Parkinson's disease and that levodopa or dopamine agonists are appropriate as initial therapy for symptoms of Parkinson's disease.

To read more about the Practice Parameters of the American Academy of Neurology, please click on the following link:

http://www.aan.com/professionals/practice/pdfs/gl0096.pdf

Dopamine agonists may also be used as second-line medication as well as MAO-B and/or COMT inhibitors or as adjuncts to enhance the effects of levodopa. Anticholergic agents or antiviral drugs may also be added on second-line therapy. There is considerable flexibility regarding which medications within each class to give first, whether to give first-line drugs as monotherapy or combination therapy, and which drugs to use as second-line therapy and when to initiate the change from first- to second-line drugs.

In general, first-line medications for the treatment of initial stages of Parkinson's disease include:

• Levodopa
• Dopamine agonists
• MAO-B inhibitor (The U.S Food and Drug Administration recently approved rasagiline as a first-line therapy for Parkinson's disease)

Second-line medications include:

• Dopamine agonists
• MAO-B inhibitors
• COMT inhibitors
• Anticholinergic agents
• Antiviral drugs

Levodopa

Until recently, levodopa was considered the "golden drug" for initial symptomatic treatment of Parkinson's disease. It became available in the 1960's and represented the first dramatic breakthrough in the treatment of Parkinson's disease. It is a highly effective drug and has been shown to extend life expectancy in Parkinson's disease patients. Before levodopa was introduced, the only agent that could relieve Parkinson's disease symptoms was anticholinergic drugs for the relief of rigidity and resting tremor. Levodopa is most effective for bradykinesia (slowness of movement) and rigidity. It is less effective for resting tremor.