Parkinson's Disease - How is the Disease Treated?
At present, there is no cure for Parkinson's disease. But a variety of medications provide dramatic relief from the symptoms.
When recommending a course of treatment, the physician determines how much the symptoms disrupt the patient's life and then tailors therapy to the person's particular condition. Since no two patients will 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 (see section entitled "Are There Other Medications Available for Managing Disease Symptoms?"), saving the most powerful treatment, specifically levodopa, for the time when patients need it most.
Levodopa
Without doubt, the gold standard of present therapy is the drug levodopa (also called L-dopa). L- Dopa (from the full name L-3,4-dihydroxyphenylalanine) is a simple chemical found naturally in plants and animals. Levodopa is the generic name used for this chemical when it is formulated for drug use in patients. 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. First introduced in the 1960s, it delays the onset of debilitating symptoms and allows the majority of parkinsonian patients -- who would otherwise be very disabled -- to extend the period of time in which they can lead relatively normal, productive lives.
Although levodopa helps at least three-quarters of parkinsonian cases, not all symptoms respond equally to the drug. Bradykinesia and rigidity respond best, while tremor may be only marginally reduced. Problems with balance and other symptoms may not be alleviated at all.
People who have taken other medications before starting levodopa therapy may have to cut back or eliminate these drugs in order to feel the full benefit of levodopa. Once levodopa therapy starts people often respond dramatically, but they may need to increase the dose gradually for maximum benefit.
Because a high-protein diet can interfere with the absorption of levodopa, some physicians recommend that patients taking the drug restrict protein consumption to the evening meal.
Levodopa is so effective that some people may forget they have Parkinson's disease. But levodopa is not a cure. Although it can diminish the symptoms, it does not replace lost nerve cells and it does not stop the progression of the disease.
Side Effects of Levodopa
Although beneficial for thousands of patients, levodopa is not without its limitations and side effects. The most common side effects are nausea, vomiting, low blood pressure, involuntary movements, and restlessness. In rare cases patients may become confused. The nausea and vomiting caused by levodopa are greatly reduced by the combination of levodopa and carbidopa which enhances the effectiveness of a lower dose. A slow-release formulation of this product, which gives patients a longer lasting effect, is also available.
Dyskinesias, or involuntary movements such as twitching, nodding, and jerking, most commonly develop in people who are taking large doses of levodopa over an extended period. These movements may be either mild or severe and either very rapid or very slow. The only effective way to control these drug-induced movements is to lower the dose of levodopa or to use drugs that block dopamine, but these remedies usually cause the disease symptoms to reappear. Doctors and patients must work together closely to find a tolerable balance between the drug's benefits and side effects.
Other more troubling and distressing problems may occur with long-term levodopa use. Patients may begin to notice more pronounced symptoms before their first dose of medication in the morning, and they can feel when each dose begins to wear off (muscle spasms are a common effect). Symptoms gradually begin to return. The period of effectiveness from each dose may begin to shorten, called the wearing-off effect. Another potential problem is referred to as the on-off effect -- sudden, unpredictable changes in movement, from normal to parkinsonian movement and back again, possibly occurring several times during the day. These effects probably indicate that the patient's response to the drug is changing or that the disease is progressing.
One approach to alleviating these side effects is to take levodopa more often and in smaller amounts. Sometimes, physicians instruct patients to stop levodopa for several days in an effort to improve the response to the drug and to manage the complications of long-term levodopa therapy. This controversial technique is known as a "drug holiday." Because of the possibility of serious complications, drug holidays should be attempted only under a physician's direct supervision, preferably in a hospital. Parkinson's disease patients should never stop taking levodopa without their physician's knowledge or consent because of the potentially serious side effects of rapidly withdrawing the drug.
