Parkinson's disease is a neurological disease that gets progressively worse with time. It is characterized by problems with neurons in the brain that are responsible for release of a chemical known as dopamine. Symptoms of Parkinson's disease include rigidity, tremor, slowness of movement, disruption of gait and typical "masked facies" appearance. There are quite a few medications that are used for treatment, but all carry their own side effect profile.
Levodopa/Carbidopa
The levodopa in this drug formulation crosses into the brain and is converted into dopamine there, while the carbidopa functions to allow greater concentrations of levodopa to actually enter the brain. Disruptions in movement are a common side effect such as chewing-like motions of the mouth, tongue protrusion, and involuntary movements of the hands and/or feet. Psychiatric side effects such as agitation, depression, anxiety, euphoria and psychotic symptoms have been noted and are results of the increased levels of dopamine in the brain. Other side effects include gastrointestinal complaints (nausea, vomiting, weight loss), excess sweating, low blood pressure (especially upon standing) and neuroleptic malignant syndrome (increased heart rate, rigidity, body temperature elevation and changes in mental status especially upon drug cessation).
Dopamine Receptor Agonists
These include drugs such as pramipexole, pergolide, and bromocriptine. They work by stimulating the dopamine receptors in a similar fashion to dopamine itself, which not only treats symptoms but can also cause side effects. Psychiatric side effects such as insomnia, euphoria, agitation, fatigue and hallucinations can occur. In addition the patient can suffer from changes in weight, nausea and vomiting, decreased blood pressure (especially on standing) and unusual body movements.
Selegiline
This medication belongs to a class of drugs known as monoamine oxidase-B inhibitors (MAO-B). Patients should be warned that ingesting foods high in a substance known as tyramine (such as wine, cheese, beer, etc.) present a risk of suffering a hypertensive crisis (increased blood pressure, headache, chest pain, nausea, sweating and disruptions in heart rate). Using this medication with another class of medications known as serotonin inhibitors can result in serotonin syndrome, which causes symptoms including flushing, sweating, nausea and vomiting, increased blood pressure and altered mental status. Other side effects include problems with urinating, gastrointestinal disruptions (nausea, vomiting, constipation), altered mood and swelling of the feet and legs.
COMT Inhibitors
Drugs in this class include tolcapone and entacapone and serve as adjuncts to levodopa therapy by prolonging the duration of action of levodopa. Side effects include diarrhea, hallucinations, low blood pressure (especially upon standing), liver toxicity (especially with tolcapone) and unexplained blood in the urine (known as hematuria). In addition, psychiatric symptoms such as pathologic behavior (including gambling and hyper-sexual behavior), anxiety, irritability and psychosis are also seen in patients due to the increased dopamine levels present.
Anticholinergic Agents
Examples of medications that belong to the anticholinergic class include benztropine, diphenhydramine and trihexyphenidyl. Most anticholinergic drugs have very similar side effects, especially in elderly patients that have a decreased ability to metabolize and eliminate the medications from their bloodstream. Ocular symptoms include blurriness and possible worsening of glaucoma. They can also decrease sweating and heat release from the body, resulting in increased body temperatures. Urinary disruptions can occur as well such as retention of urine. The central nervous system can also be affected with symptoms such as confusion, memory impairment, anxiety, hallucinations and disorientation.
Amantadine
This is normally an antiviral agent used against influenza. The central nervous system can be affected and can cause irritability, headache, agitation, depression and nightmares. Light-headedness and low blood pressure can also occur, especially upon standing. Gastrointestinal complaints such as nausea, vomiting, diarrhea, constipation and decreased appetite can also occur. A unique purplish skin discoloration known as "livedo reticularis" can also result and is usually attributable to decreased blood flow and skin temperature in the extremities such as the foot.
References
- "Medical Treatment of Parkinson's Disease"; Stacy, M.; Neurologic Clinics, Volume 27, August 2009
- "The Scientific and Clinical Bias for the Treatment of Parkinson's Disease; Olanow, CW et al.; Neurology, Volume 72, May 2009
- Neurology in Clinical Practice, 5th Edition; Bradley, W; 2008
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