Parkinson’s disease is a progressive disease that occurs when certain cells in the brain that produce dopamine deteriorate. Dopamine is a chemical signal essential for nervous system control of muscle movement. The onset of symptoms – a slight tremor, loss of balance, rigid limbs, decreased facial expressions – happens gradually. Even after drug treatment becomes necessary, many patients have years before serious complications arise.
During early stages of Parkinson’s, the doctor might wait to prescribe drugs until symptoms begin to interfere with daily activities. Exercise, physical therapy and occupational therapy can be helpful at all stages of Parkinson’s disease. Simplifying daily activities to conserve energy for essential tasks is also recommended. There is no cure or treatment that slows the progression of Parkinson’s; however, there are drugs that are effective at controlling symptoms.
Medications used to treat Parkinson’s disease aim to correct the dopamine deficiency in the brain. For most patients, the drug of first choice is levodopa/carbidopa (Sinemet, Parcopa and various generic products). It passes into the brain and is converted into dopamine. As the disease progresses, the benefit from levodopa/carbidopa therapy can wax and wane, requiring medication adjustments or additions. Common side effects of levodopa/carbidopa products include involuntary movements (dyskinesias), nausea, confusion or hallucinations.
Dopamine agonists, another class of Parkinson’s drugs, boost the effects of dopamine. They might be the first agent used in people with mild symptoms. Pramipexole (Mirapex) and ropinirole (Requip) are the two most frequently used medications in this class. Longer duration of action per dose of medication and the ability to smooth the on and off effects of levodopa are two benefits associated with these medications. Possible side effects of dopamine agonists include hallucinations, sleepiness, water retention and low blood pressure when standing. These medications might also increase the risk of compulsive behaviors.
Monoamine oxidase type B (MAO-B) inhibitors and catechol O-methyltransferase (COMT) inhibitors help prevent the breakdown of dopamine and levodopa. Selegiline (Eldepryl) and rasagiline (Azilect) are the most common MAO-B inhibitors, and entacapone is the most common COMT inhibitor. Entacapone is available by itself (Comtan) or combined with carbidopa and levodopa in a medication called Stevelo. Adjustment in levodopa/carbidopa doses might be required if entacapone is added to minimize side effects. The side effects of MAO-B inhibitors are rare but can include confusion, headache,
hallucinations, and dizziness. The MAO-B inhibitors shouldn’t be used with many herbal supplements and other drugs, especially some antidepressants.
A class of drugs known as anticholinergics, which includes benztropine (Cogentin) and amantadine (Symmetrel), has been used to help control the tremor associated with Parkinson’s disease. A number of these drugs are available; however, their modest benefits are often offset by side effects such as impaired memory, confusion, constipation, dry mouth and eyes, and impaired urination.
Nearly 5 million people globally have Parkinson’s disease. The underlying cause remains elusive and the available drugs do not cure the disease, but with careful management they may help to control symptoms, prolong independence and maintain the highest possible quality of life. Combination of two or more drug classes often becomes necessary as the disease progresses from mild to more severe forms. Drug regimens are highly individualized and should be monitored and managed by an experienced doctor.
Chris Froelich is a Doctor of Pharmacy candidate on rotation at St. Patrick Hospital.