8.11 Anti-Parkinson’s Medications
Parkinson’s disease is believed to be related to an imbalance of dopamine and acetylcholine and a deficiency of dopamine in certain areas of the brain, so drug therapies are aimed at increasing levels of dopamine and/or antagonizing the effects of acetylcholine. Drug therapy does not cure the disease but is used to slow the progression of symptoms. Common medications used to treat Parkinson’s disease are carbidopa/levodopa, selegiline, and amantadine.
Carbidopa/Levodopa
Carbidopa/levodopa is the most common drug used to treat Parkinson’s disease and is usually started as soon as the client becomes functionally impaired.
Mechanism of Action: Administration of dopamine is ineffective in the treatment of Parkinson’s disease because it does not cross the blood-brain barrier, but levodopa, the metabolic precursor of dopamine, does cross the blood-brain barrier and presumably is converted to dopamine in the brain. Carbidopa is combined with levodopa to help stop the breakdown of levodopa before it is able to cross the blood-brain barrier. Additionally, the incidence of levodopa-induced nausea and vomiting is less when it is combined with carbidopa.
Indications: Carbidopa/levodopa is indicated for Parkinson’s disease. It is also used to treat restless leg syndrome.
Nursing Considerations: Carbidopa/levodopa is recommended for use in clients older than age 18. It can take several weeks to see positive effects, and this should be explained to clients and their caregivers.
The drug is contraindicated for use with MAOIs. All clients should be observed carefully for the development of depression with concomitant suicidal tendencies.
Clients taking carbidopa and levodopa have reported suddenly falling asleep without prior warning of sleepiness while engaged in activities of daily living (including operation of motor vehicles). Clients should be advised to exercise caution while driving or operating machines during treatment with carbidopa and levodopa.
Sporadic cases of symptoms resembling neuroleptic malignant syndrome (NMS) have been reported in association with dose reductions or withdrawal of certain anti-Parkinsonian agents. Therefore, clients should be observed carefully when the dosage of levodopa is reduced abruptly or discontinued.
Periodic evaluations of hepatic, hematopoietic, cardiovascular, and renal functions are recommended during extended therapy. The most common adverse effect of carbidopa/levodopa is dyskinesia, which may require dosage reduction.
Clients should be instructed to plan their mealtimes around medication times to improve the ability to use their utensils and to avoid diets high in protein due to decreased absorption of the medication.
Side Effects/Adverse Effects: Hallucinations and psychotic-like behavior have been reported with dopaminergic medications. Clients taking dopaminergic medications may experience intense gambling urges, increased sexual urges, intense urges to spend money, binge eat