Some Side Effects
Levodopa (given with carbidopa)
For levodopa: Involuntary movements (of the mouth, face, and limbs), nightmares, low blood pressure when a person stands up (orthostatic hypotension), constipation, nausea, drowsiness, confusion, hallucinations, paranoia, palpitations, and flushing
If these drugs are suddenly stopped, neuroleptic malignant syndrome (with high fever, high blood pressure, muscle stiffness, muscle damage, and coma), which can be life threatening
This combination is the mainstay of treatment. Carbidopa helps increase the effectiveness of levodopa and reduce its side effects. After several years, the effectiveness of the combination may lessen.
Drowsiness, nausea, orthostatic hypotension, involuntary movements, confusion, obsessive-compulsive behavior, new or increased urges (such as gambling), and hallucinations
When these drugs are suddenly stopped, neuroleptic malignant syndrome
Early in the disease, these drugs may be used alone or with small doses of levodopa to possibly delay levodopa’s side effects. Later in the disease, dopamine agonists are useful when the on-off effects of levodopa make it less effective. These drugs are especially useful in people under 60.
Severe nausea, vomiting, and lumps (nodules) under the skin at the injection site
This quick-acting drug is injected under the skin. It is used as rescue therapy to reverse the off effects of levodopa.
Drowsiness, nausea, orthostatic hypotension, confusion, obsessive-compulsive behavior, new or increased urges (such as gambling), hallucinations, weight gain (possibly due to fluid retention), and sometimes skin irritation where the patch is applied
Rotigotine is available as a skin patch. It is used alone, early in the disease. The patch is worn continuously for 24 hours, then removed and replaced. The patch should be placed in different locations each day to reduce risk of skin irritation.
Nausea, insomnia, drowsiness, and swelling due to fluid accumulation (edema)
Rasagiline can be used alone to postpone the use of levodopa but is often given as a supplement to levodopa. At best, rasagiline is modestly effective.
When given with levodopa, worsening of levodopa's side effects, including nausea, confusion, insomnia, and involuntary movements
Selegiline can be used alone to postpone the use of levodopa but is often given as a supplement to levodopa. At best, selegiline is modestly effective.
When given with levodopa, possibly worsening of levodopa's side effects, including nausea, confusion, and involuntary movements
Diarrhea, back pain, and orange urine
Rarely with tolcapone, risk of liver damage
These drugs can be used to supplement levodopa late in the disease and to extend the interval between doses of levodopa. They are used only with levodopa.
When tolcapone is used, doctors periodically do blood tests to evaluate how well the liver is functioning and whether it is damaged (liver tests)
Tricyclic antidepressants (such as amitriptyline), used if depression also needs to be treated
Some antihistamines (such as diphenhydramine)
Drowsiness, confusion, dry mouth, blurred vision, dizziness, constipation, difficulty urinating, loss of bladder control, and impaired regulation of body temperature
These drugs may be given alone in the early stages to young people whose most troublesome symptom is tremor. These drugs can reduce tremor but do not affect slow movements or relieve muscle stiffness.
Doctors try to avoid using these drugs in older people because the side effects are particularly troublesome for older people.
Nausea, dizziness, insomnia, anxiety, confusion, edema, difficulty urinating, worsening of glaucoma, and mottled discoloration of the skin due to dilated blood vessels (livedo reticularis)
Rarely, when the drug is stopped or the dose is reduced, neuroleptic malignant syndrome
Amantadine is used alone in the early stages for mild disease but may become ineffective after several months. Later, it is used to supplement levodopa and to lessen involuntary movements due to levodopa.
* Anticholinergic drugs are seldom used to treat Parkinson disease because they are only mildly effective and have troublesome side effects.
COMT = catechol O-methyltransferase; MAO-B = monoamine oxidase type B.