In order to understand the medications for Parkinson's disease, one must first understand the pathophysiology of this disease
Our neurons release a chemical called Dopamine that is responsible for the contraction and relaxation of involuntary muscles in order to maintain balance and fine motor skills. Parkinson’s disease is a condition where degeneration and necrosis of neurons occur, which cause insufficient dopamine secretion leading to a variety of symptoms including trembling limbs, slow movement, and muscle stiffness. These symptoms of Parkinson’s disease are not limited to the muscles of the limbs, but can spread to fingers, mouth, and even to the urinary and/or defecation systems as the disease progresses over time. Cognitive skills such as thinking and memory may also deteriorate as the disease progresses.
Parkinson’s disease is a chronic degenerative disease. In the early stages of the disease, the patient still has the capability to manage daily life tasks, however, as the disease progresses after 8-10 years, the patient may need assistance with simple daily activities. Unfortunately, Parkinson’s disease is still an incurable disease with no new breakthroughs in treatment for the past 10 years. This piece of discouraging information often creates a difficult psychological hurdle for patients and their caregivers to overcome.
The following Parkinson's disease medications are used to alleviate the symptoms of the disease in order to prolong the time that patients can take care of their own daily activities. That is, all current Parkinson’s disease medications do not have the ability to cure the disease.
Levodopa/Carbidopa is a common medication prescribed to Parkinson’s patients as it provides the best symptomatic relief. When absorbed, the drug will be converted to dopamine to supplement the lack of dopamine caused by the degeneration and necrosis of neurons.
When starting this medication, it can be taken two to three times daily with the effect of each dose lasting about 6-8 hours. However, after taking Levodopa/Carbidopa for 5 to 8 years, the duration of effect of each dose will be significantly shortened to 4-5 hours or even shorter. A temporary solution to this may be to add or switch to a controlled release formula. Unfortunately, controlled release formulas will also experience similar shortening of duration of effect over time.
Common side effects of the Levodopa/Carbidopa include upset stomach, orthostatic hypotension (dizziness caused by poor blood pressure regulation when the body quickly shifts from a sitting to standing position), and involuntary convulsions. Hallucination can also be a side effect, but is less commonly seen.
An important note is that when taking Levodopa/Carbidopa, after taking for a prolonged period of time, it cannot be stopped without consultation. Parkinson’s disease patients often experience stiffness in their limb muscles when they forget to take a dose, stopping all doses at once will lead to an Akinetic crisis where the limbs feel frozen and are not able to move.
Dopamine agonist (eg. Pramipexole, Ropinirole)
The symptom relieving effects of Dopamine agonists are not as good as Levodopa/Carbidopa. However, shortening of the drug’s duration of effect does not occur in Dopamine agonists as it does in Levodopa/Carbidopa. Dopamine agonists may be solely prescribed in the early stages of the disease. A switch to Levodopa/Carbidopa may be needed in the later stages of the disease as the drug is unable to manage the severity of the disease. Dopamine agonists can also be used together with Levodopa/Carbidopa if necessary.
Side effects include gastrointestinal system disturbances, orthostatic hypotension, hallucination, and drowsiness. Similar to Levodopa/Carbidopa, Dopamine agonists must be consistently administered and cannot be stopped without consultation. Stopping medication can lead to symptoms of withdrawal syndrome, including anxiety, tiredness, and sweating.
Anticholinergic drugs (eg. Benztropine, trihexyphenidyl)
Anticholinergic drugs can relieve the tremors caused by Parkinson's disease, however, the overall symptoms relieving effect is not as good as Levodopa/Carbidopa and Dopamine agonists. Additionally, the side effects of Anticholinergic drugs such as dry mouth, constipation, and lethargy can be difficult for patients to tolerate, hence, making it harder to increase the dose. Therefore, it can only be used as a complementary drug in addition to other Parkinson’s disease medications. Hallucinations and drowsiness are also side effects that can occur after taking Anticholinergic drugs.
COMT inhibitors (eg. Entacapone)
COMT inhibitors reduce the deactivation of Levodopa/Carbidopa outside of the brain to increase the levels of Levodopa/Carbidopa that are able to reach the brain. Hence, COMT inhibitors are often used together with Levodopa/Carbidopa as it does not have the abilities to relieve Parkinson’s disease symptoms alone. When the duration of action of Levodopa/Carbidopa is starting to shorten from dosing three times daily to four times daily, COMT inhibitors, such as Entacapone can be added to each Levodopa/Carbidopa dose with hopes to slow down the shortening duration of action of Levodopa/Carbidopa.
In addition, the progression of Parkinson’s disease and the drugs used may lead the patient to different degrees of mental illnesses including hallucinations and depression. If such symptoms are found in the patient or caregivers, consult with a specialist doctor to determine if drugs are needed to control the symptoms.
Everyone’s response to Parkinson’s disease medication is different. Therefore, if the medication prescribed by your doctor is not performing as expected, record the symptoms or side effects and consult your doctor if any dose/medications adjustments are necessary. By adjusting the medication or dosage, there is hope that the patient’s quality of life can be improved.
Although Parkinson’s disease is still incurable, patients and caregivers can participate in community organizations specifically designed for Parkinson’s patients to share their experiences and support each other through their own journeys which can be of great benefit to the patient and caregiver’s mental health. Consultation with a professional physiotherapist for advice on how to exercise and balance at different stages of Parkinson's disease is also recommended.