Artane

Definition

Antiparkinson drugs are medicines that relieve the symptoms of Parkinson's disease and other forms of parkinsonism.

Purpose

Antiparkinson drugs are used to treat symptoms of parkinsonism, a group of disorders that share four main symptoms: tremor or trembling in the hands, arms, legs, jaw, and face; stiffness or rigidity of the arms, legs, and trunk; slowness of movement (bradykinesia); and poor balance and coordination. Parkinson's disease is the most common form of parkinsonism. Other forms of the disorder may result from viral infections, environmental toxins, carbon monoxide poisoning, and other causes.

All types of parkinsonism occur when nerve cells in a particular part of the brain die or lose the ability to function. These cells normally produce a chemical called dopamine, a chemical messenger that helps relay signals to different parts of the brain. This process is important in producing smooth, coordinated movement throughout the body. When dopamine-producing cells are lost, normal movement becomes impossible. In people with late-stage Parkinson's disease, 80% or more of these important cells are dead or impaired.

No cure for Parkinson's disease or other forms of parkinsonism exists, but several drugs help relieve the symptoms. Some drugs, such as levodopa, replenish dopamine in the brain. Others mimic the role of dopamine or block the effects of other chemicals that cause problems in the brain when dopamine levels drop.

Description

The drugs described here are of two types:

• Levodopa, which is used alone or in combination with carbidopa, restores dopamine levels in the brain. Carbidopa helps make levodopa more effective and reduces some of the side effects that occur when levodopa is taken by itself.
• Antidyskinetics and anticholinergics, such as benztropine and trihexyphenidyl, block the effects of other brain chemicals, thereby reducing some of the involuntary tremors.

The products Sinemet and Sinemet CR contain combinations of levodopa and carbidopa. Some commonly used anticholinergics are trihexyphenidyl (Artane) and benztropine mesylate (Cogentin). All antiparkinson drugs are available only with a physician's prescription. They are sold in tablet (regular and extended-release), liquid, extended-release capsule, and injectable forms.

Other medicines, such as bromocriptine and pergolide, selegiline, and the antiviral drug amantadine, are also sometimes used alone or in combination with other antiparkinson drugs to treat Parkinson's disease.

Recommended dosage

The recommended dosage depends on the type of antiparkinson drug. Finding the correct dose for a particular patient is a process that may take time and patience. The physician tries to tailor the treatment to the patient, taking into account what symptoms the patient has and how much the symptoms interfere with normal life. No two patients react the same to a particular drug, so a person may need to try different drugs and different dosages before finding the best treatment. For people with mild symptoms, physicians may prescribe less powerful drugs at first, saving levodopa for later, when symptoms are more severe.

Always take antiparkinson drugs exactly as directed. Never take larger or more frequent doses. Physicians may sometimes recommend a "drug holiday," during which a patient stops taking the medicine for short time. This should be done only under a physician's supervision, preferably in a hospital. Patients should not take drug holidays on their own.

Several weeks or even months may be needed for the full effects of this medicine to be felt. Be sure to keep taking it as directed, even if it does not seem to be helping.

Do not stop taking this medicine without first checking with the physician who prescribed it. Gradually tapering the dose may reduce the chance of side effects and prevent symptoms from getting worse.

Precautions

Seeing a physician regularly is important while taking antiparkinson drugs, especially during the first few months. The physician will check to make sure the medicine is working as it should and will note unwanted side effects. The physician may also need to adjust the dosage during this period.

Antiparkinson drugs may add to the effects of alcohol and other drugs that slow down the central nervous system, such as antihistamines, cold medicine, allergy medicine, sleep aids, medicine for seizures, tranquilizers, some pain relievers, and muscle relaxants. Anyone taking antiparkinson drugs should check with his or her physician before using any of the above.

Antiparkinson drugs may interact with medicines used during surgery, dental procedures, or emergency treatment. These interactions could increase the chance of side effects. Anyone who is taking antiparkinson drugs should be sure to tell the health care professional in charge before having any surgical or dental procedures or receiving emergency treatment.

Some people feel drowsy, dizzy, or less alert when using these drugs. The drugs may also cause blurred vision. Because of these possible problems, anyone who takes these drugs should not drive, use machines or do anything else that might be dangerous until they have found out how the drugs affect them.

Antiparkinson drugs make some people feel lightheaded, dizzy, or faint when they get up after sitting or lying down. To lessen the problem, get up gradually and hold onto something for support if possible.

People taking antiparkinson drugs may sweat less, which can cause the body temperature to rise. Anyone who takes this medicine should be careful not to become overheated during exercise or hot weather and should avoid hot baths, hot tubs, and saunas. Overheating could lead to heat stroke.

Diets high in protein may interfere with the effects of levodopa. People taking this medicine should eat only moderate amounts of protein, spaced throughout the day. Check with a physician or dietitian about how much protein should be consumed on a daily basis.

Vitamin B₆ reduces the effects of levodopa when levodopa is taken alone, but this is not a problem when levodopa is taken with carbidopa. Anyone taking levodopa by itself should not take vitamin supplements that contain vitamin B₆ unless told to do so by a physician. Some foods, such as avocados, beans, sweet potatoes, peas, tuna, bacon, beef liver, pork, dry skim milk, oatmeal, and some health foods, contain high levels of vitamin B₆. Check with a physician about how much of these foods may be eaten while taking levodopa.

Older people may also be more sensitive to the effects of antiparkinson drugs, and thus more likely to have side effects.

Children may be particularly sensitive to the effects of antidyskinetics. This sensitivity increases the chance of side effects. The effects of levodopa and carbidopa on children have not been studied.

Antidyskinetics may make the eyes more sensitive to light. To lessen the discomfort, wear sunglasses and avoid bright light. Patients taking this medicine may need to have their eyes examined by an ophthalmologist before and during treatment.

Antidyskinetics may cause dry mouth. To temporarily relieve the discomfort, chew sugarless gum, suck on sugarless candy or ice chips, or use saliva substitutes, which come in liquid and tablet forms and are available without a prescription. If the problem continues for more than 2 weeks, check with a physician or dentist. Mouth dryness that continues over a long time may contribute to tooth decay and other dental problems.

Levodopa may dramatically improve symptoms, but patients should be careful not to overdo physical activities as movement becomes easier. Physical activity should be increased only gradually. This is especially important for older people and people who have been inactive for some time.

Taking levodopa over a long time can lead to a problem called the "on-off" effect, in which a patient suddenly becomes unable to move. The effect may last only a few minutes or as long as several hours. When it ends, the patient is able to move normally again, but the effect may occur again and again without warning. A patient who experiences this problem should check with a physician.

Another possible problem with long-term use of levodopa is called the "wearing-off" effect. With this effect, patients notice more pronounced symptoms as each dose wears off. Changing the dose of the medicine and the frequency with which it is taken may help prevent this effect. Patients who have this problem should check with their physicians and should not change the dose of their medicine themselves.

Special conditions

People with certain medical conditions or who are taking certain other medicines can have problems if they take antiparkinson drugs. Before taking these drugs, be sure to let the physician know about any of these conditions:

Anyone who has had unusual reactions to antiparkinson drugs in the past should let his or her physician know before taking the drugs again. The physician should also be told about any allergies to foods, dyes, preservatives, or other substances.

Antiparkinson drugs may cause false results on some urine tests for sugar or ketones. Persons with diabetes who take this medicine should check with their physicians.

Studies of laboratory animals show that levodopa, alone or in combination with carbidopa, may cause birth defects when taken during pregnancy. The drugs' effects on pregnant women have not been studied. The effects of antidyskinetics on pregnancy have not been studied in humans. Women who are pregnant or who may become pregnant should check with their physicians before using any antiparkinson drug.

Breastfeeding

Levodopa and carbidopa pass into breast milk and may cause unwanted side effects in nursing babies whose mothers take this medicine. Levodopa also may reduce the flow of breast milk. Whether antidyskinetics pass into breast milk and affect nursing babies is unknown. Women who are breastfeeding should check with their physicians before using any antiparkinson drug.

Before using antiparkinson drugs, people with any of these medical problems should make sure their physicians are aware of their conditions:

• Heart or blood vessel disease
• High blood pressure
• Kidney disease
• Liver disease
• Chronic lung disease such as asthma, emphysema, or bronchitis
• Diabetes
• Hormone problems
• Intestinal blockage
• Stomach ulcer, now or in the past
• Difficult urination or enlarged prostate
• Glaucoma
• Melanoma (a type of skin cancer)
• Epilepsy or other seizure disorders
• Mental illness
• Myasthenia gravis
• Uncontrolled movements of the hands, mouth, or tongue.

Taking antiparkinson drugs with certain other drugs may affect the way the drugs work or may increase the chance of side effects.

Side effects

Antidyskinetics

The most common side effects of antidyskinetics are drowsiness; nausea and vomiting; constipation; difficult or painful urination; dry mouth, nose, or throat; blurred vision; increased sensitivity of the eyes to light; and decreased sweating. These problems usually go away as the body adjusts to the drug and do not require medical treatment unless they continue or they interfere with normal activities.

More serious side effects are rare, but may occur. Check with the physician who prescribed the medicine as soon as possible if confusion, eye pain, or skin rash occur.

Other symptoms may occur if too much of this drug is taken. Get emergency medical help immediately if any of these signs of overdose occur:

• Severe drowsiness
• Clumsiness or unsteadiness
• Fast heartbeat
• Breathing problems
• Seizures (convulsions)
• Severely dry mouth, nose, or throat
• Unusual warmth, dryness, and flushing of skin
• Hallucinations
• Mood or mental changes
• Sleep problems.

The effects of this medicine may continue for some time after patients stop taking it. Check with a physician if any of these symptoms occur after stopping treatment with antidyskinetics:

• Dizziness when getting up from sitting or lying down
• Poor balance
• Muscle spasms, especially in the face, neck, and back
• Restlessness
• Shuffling walk
• Stiff or rigid arms or legs
• Trembling or shaking of the hands and fingers
• Twisting movements of the body
• Problems with talking or swallowing
• Expressionless, mask-like face
• Fast heartbeat
• Anxiety
• Sleep problems.

Levodopa

The most common side effects are anxiety, nervousness, and confusion. These problems usually go away as the body adjusts to the drug and do not require medical treatment unless they continue or they interfere with normal life. Levodopa also may turn urine and sweat a dark color. This is normal.

More serious side effects may occur. If any of the following side effects occur, check with the physician who prescribed the medicine as soon as possible:

• Dizziness or lightheadedness when getting up after sitting or lying down
• Severe or continuing nausea or vomiting
• Depression or other mood or mental changes
• Involuntary movements of the body
• Spasms or involuntary closing of the eyelids
• Irregular heartbeat
• Difficulty urinating.

Other side effects may occur with any antiparkinson drug. Anyone who has unusual symptoms after taking an antiparkinson drug should get in touch with his or her physician.

Interactions

Antiparkinson drugs may interact with other medicines. When this happens, the effects of one or both of the drugs may change or the risk of side effects may be greater. Any one who takes antiparkinson drugs should let the physician know all other medicines he or she is taking. Among the drugs that may interact with antiparkinsondrugs are:

• Other anticholinergics (some may be prescribed for spasms or cramps in the abdomen or stomach)
• Central nervous system (CNS) depressants such as medicine for allergies, colds, hay fever, and asthma; sedatives; tranquilizers; prescription pain medicine; muscle relaxants; medicine for seizures; sleep aids; barbiturates; and anesthetics
• Tricyclic antidepressants such as imipramine (Tofranil) or desipramine (Norpramin)
• Monoamine oxidase inhibitors (MAO inhibitors) such as phenelzine (Nardil) or tranylcypromine (Parnate)
• Antipsychotic drugs such as haloperidol (Haldol), chlorpromazine (Thorazine), and thioridazine (Mellaril)
• Cocaine
• Vitamin B₆ (pyridoxine)
• Selegiline (Eldepryl) - a drug often given along with levodopa or levodopa-carbidopa to enhance the effects of those drugs
• The antiseizure medicines phenytoin (Dilantin) or ethotoin (Peganone).

The list above does not include every drug that may interact with antiparkinson drugs. Be sure to check with a physician or pharmacist before combining antiparkinson drugs with any other prescription or nonprescription (over-the-counter) medicine.

Key Terms

Bradykinesia

Extremely slow movement.

Carbon monoxide

A colorless, odorless, highly poisonous gas.

Central nervous system

The brain, spinal cord and nerves throughout the body.

Chronic

A word used to describe a long-lasting condition. Chronic conditions often develop gradually and involve slow changes.

Glaucoma

A condition in which pressure in the eye is abnormally high. If not treated, glaucoma may lead to blindness.

Hallucination

A false or distorted perception of objects, sounds, or events that seems real. Hallucinations usually result from drugs or mental disorders.

Heat stroke

A severe condition caused by prolonged exposure to high heat. Heat stroke interferes with the body's temperature regulating abilities and can lead to collapse and coma.

Parkinsonism

A group of conditions that all have these typical symptoms in common: tremor, rigidity, slow movement, and poor balance and coordination.

Prostate

A donut-shaped gland below the bladder in males that contributes to the production of semen.

Seizure

A sudden attack, spasm, or convulsion.

Spasm

Sudden, involuntary tensing of a muscle or a group of muscles.

Tremor

Shakiness or trembling.

Further Reading

For Your Information

Organizations

• American Parkinson Disease Association. Address: 60 Bay Street, Suite 401, Staten Island, NY 10301. Telephone: 800-223-2732.
• National Institute of Neurological Disorders and Stroke. Address: P.O. Box 5801, Bethesda, MD 20824. Telephone: 800-352-9424.
• National Parkinson Foundation, Inc. Address: 1501 N.W. 9th Avenue, Miami, FL 33136-1494. Telephone: 800-327-4545.

Gale Encyclopedia of Medicine. Gale Research, 1999.