When recommending a course of treatment, the physician determines how much the symptoms disrupt the patient's life, and then tailors the therapy to the patient's particular condition. Since no two patients react the same way to a given drug, it may take time and patience to get the dose just right. Even then, symptoms may not be completely alleviated. In the early stages of Parkinson's disease, physicians often begin treatment with one or a combination of the less powerful drugs, such as the anticholinergics or amantadine, and save the most powerful treatments, specifically levodopa, for the time when patients need it most. Levodopa is the generic name used for this chemical when it is formulated for use as a drug.
Nerve cells can use levodopa to make dopamine and replenish the brain's dwindling supply.
Dopamine itself cannot be given because it doesn't cross the blood-brain barrier, the elaborate meshwork of fine blood vessels and cells that filters blood reaching the brain. Usually, patients are given levodopa combined with carbidopa. When added to levodopa, carbidopa delays the conversion of levodopa into dopamine until it reaches the brain, preventing or diminishing some of the side effects that often accompany levodopa therapy. Carbidopa also reduces the amount of levodopa needed. Levodopa's success in treating the major symptoms of Parkinson's disease is a triumph of modern medicine.