Parkinson's disease is a neurological disorder caused by damage to dopamine-producing cells. The lack of dopamine in the brain results in mobility problems, according to the National Institutes of Health (NIH). Medication for Parkinson's disease works by increasing the amount of dopamine in the brain; however, these medications have a limited therapeutic window, and will only alleviate symptoms for small amounts of time.
Levodopa
Levodopa is the first choice of medication when treating Parkinson's disease. This drug works by crossing the blood-brain barrier, then changing into the neurotransmitter dopamine. By increasing the amount of dopamine in the patient's body, levodopa decreases the severity of the Parkinson's disease symptoms. The National Institute of Neurological Disorders and Stroke (NINDS) notes that 75 percent of patients who use levodopa have improvements. Levodopa is most effective with bradykinesia, or slowed movement, and rigidity. Levodopa, however, has a limited therapeutic window, and becomes less effective as Parkinson's disease gets worse.
Carbidopa
Carbidopa is another medication for Parkinson's disease, and is given with levodopa. Carbidopa is a supportive drug, as it works by preventing levodopa from converting into dopamine until the drug reaches the brain. If levodopa becomes dopamine before reaching the brain, it cannot cross the blood-brain barrier, as the dopamine molecule is too large. Besides delaying levodopa's conversion, carbidopa also prevents nausea.
Dopamine Agonists
Dopamine agonists also treat the symptoms of Parkinson's disease, but affect dopamine differently than levodopa. Instead of increasing the amount of dopamine through production, dopamine agonists trick the brain by acting like dopamine. Examples of dopamine agonists for Parkinson's disease include pramipexole, rotigotine, ropinirole and bromocriptine. While dopamine agonists are not as effective as levodopa, they have a longer therapeutic window.
Anticholinergics
Anticholinergics control the severity of tremors and rigidity, and may be chosen over levodopa if the patient has more prevalent tremors than other symptoms. Examples of anticholinergics are benztropine and trihexyphenidyl. The Mayo Clinic notes that the side effects of anticholinergics, like hallucinations, may outweigh the benefits in Parkinson's disease patients who are older than the age of 70.
