Medical Treatment for Parkinson's Disease
There is no cure for Parkinson's disease. Treatment centers on the administration of medication to relieve symptoms. The Food and Drug Administration (FDA) also has approved a surgically-implanted device that lessens tremors. In some severe cases, a surgical procedure may offer the greatest benefit.
Medications to Treat Parkinson's
Medication selection and dosage is tailored to each individual patient. In deciding on a treatment, the physician considers factors such as severity of symptoms, age, and presence of other medical conditions. No two patients respond identically to a particular drug or dosage level, so this process involves experimentation, persistence, and patience.
As Parkinson's disease progresses, drug dosages may have to be modified and medication regimens changed. Sometimes a combination of drugs is given.
Levodopa and carbidopa combined (Sinemet®) is the mainstay of Parkinson's therapy. Levodopa is rapidly converted into dopamine by the enzyme dopa decarboxylase (DDC), which is present in the central and peripheral nervous systems. Much of levodopa is metabolized before it reaches the brain.
Carbidopa blocks the metabolism of levodopa in the liver, decreasing nausea and increasing the amount of levodopa that reaches the brain. Levodopa is most effective in treating bradykinesia and rigidity, less effective in reducing tremor, and often ineffective in relieving problems with balance.
Side effects include nausea, especially early in treatment, low blood pressure (hypotension), and abnormal movements (dyskinesias). Slow dosage adjustment and taking medication with food can reduce these effects and using the lowest effective dose may prevent or delay the appearance of motor dysfunction. Levodopa can become ineffective over time.
Depression, confusion, and visual hallucinations also may occur with these medications, especially in the elderly.
Dopamine Agonists to Treat Parkinson's
Dopamine agonists mimic dopamine's function in the brain. They are used primarily as adjuncts to levodopa/carbidopa therapy. In some cases, these drugs are used as monotherapy, but they are generally less effective in controlling symptoms. Side effects are similar to those produced by levodopa and include nausea, sleepiness, dizziness, and headache.
Dopamine agonists include the following:
- Bromocriptine (Parlodel®)
- Pramipexole (Mirapex®)
- Ropinirole (Requip®)
Amantadine (Symmetryl®) is an antiviral drug with dopamine agonist properties. It increases the release of dopamine and is often used to treat early-stage Parkinson's disease, either alone, with an anticholinergic drug, or with levodopa. Generally, it loses its effectiveness within 3 to 4 months.
Side effects of amantadine include mottling of the skin, edema, confusion, blurred vision, insomnia, and anxiety.
MAO-B Inhibitors to Treat Parkinson's
Dopamine is oxidized by monoamine oxidase B (MAO-B). Rasagiline (Azilect®) and selegiline (Carbex®) inhibit MAO-B, increasing the amount of available dopamine in the brain. MAO-B inhibitors boost the effects of levodopa.
Side effects may include nausea, dizziness, abdominal pain, confusion, hallucinations, and dry mouth. MAO-B inhibitors are contraindicated for patients taking tricyclic antidepressants (e.g., Pamelor®) , SSRIs (e.g., Prozac®), or meperidine (Demerol®) and other opiates. Patients who are taking MAO-B inhibitors must follow their physician's recommendations regarding a number of dietary precautions.
Anticholinergics to Treat Parkinson's
Anticholinergics reduce the relative overactivity of the neurotransmitter acetylcholine to balance the diminished dopamine activity. This class of drugs is most effective in the control of tremor, and they are used as adjuncts to levodopa.
These drugs include the following:
- Benztropine mesylate (Cogentine®)
- Biperiden (Akineton®)
- Diphenhydramine (Benadryl®)
- Trihyxyphenidyl (Artane®)
Side effects associated with anticholinergic drugs include dry mouth, blurred vision, constipation, and urinary retention. In higher doses, these medications may impair memory.
COMT (catechol-O-methyl transferase) Inhibitors to Treat Parkinson's
These medications augment levodopa therapy by inhibiting the COMT enzyme, which breaks down dopamine after it is released in the brain. These drugs are only effective when used with levodopa.
COMT inhibitors include entacapone (Comtan®) and tolcapone (Tasmar®). Side effects of these medications include vivid dreams, visual hallucinations, nausea, sleep disturbances, daytime drowsiness, headache, and dyskinesias.
Carbidopa, levodopa, and entacapone are combined in Stalevo®, which is available in flexible dosing and indicated for patients who experience a reduced effectiveness of their PD medication.
Common side effects of Stalevo® include dyskinesias and nausea, which may be controlled by altering the dosing schedule.
Other side effects include the following:
- Abdominal pain
- Discolored urine
The Exelon® Patch (rivastigimine transdermal system) has been approved by the FDA to treat mild-to-moderate dementia associated with Parkinson's disease. This patch is applied to the skin (usually on the back, chest, or upper arm) and delivers medication continuously for 24 hours. Side effects include nausea, vomiting, diarrhea, and loss of appetite. Higher dosages of the medication increase the risk for these side effects.
Other drugs that work in a similar manor include donepezil (Aricept®) and galantamine (Razadyne®).