Levodopa, also called L-dopa, which is converted to dopamine in the brain, remains the gold standard for treating Parkinson's disease. The standard preparations (Sinemet, Atamet) combine levodopa with carbidopa, which improves the action of levodopa and reduces some of its side effects, particularly nausea. Dosages vary, although the preparation is usually taken in three or four divided doses per day.
In general L-dopa has the following effects on Parkinson's disease:
In many patients, levodopa significantly improves the quality of life for many years.
The toxic effects of levodopa with or without carbidopa are considerable.
Physical Side Effects. The physical side effects include:
Psychiatric and Mental Side Effects. The major adverse effects of the drug are psychiatric. Patients taking levodopa, especially in combination with other drugs, can experience:
Levodopa causes fewer psychiatric side effects than other drugs used for Parkinson's disease, including anticholinergics, selegiline, amantadine, and dopamine agonists. Because psychiatric side effects often occur at night, if they are severe some doctors recommend reducing or stopping the evening dose.
Within 4 - 6 years of treatment with levodopa, the effects of the drug in many patients begin to last for shorter periods of time after a dose (called the wearing-off effect) and the following pattern may occur:
Preventing the Wearing-Off Effect. To reduce the effects of fluctuation and the wearing-off effect, it is important to maintain as consistent a level of dopamine as possible. Unfortunately, levodopa is poorly absorbed and may remain in the stomach a long time. A number of strategies are being developed to take care of these problems:
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