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.^[1]

Carbidopa/Levodopa

Carbidopa/levodopa is the most common drug used to treat Parkinson’s disease and is usually started as soon as the patient 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 patients older than age 18. It can take several weeks to see positive effects, and this should be explained to patients and their caregivers.

The drug is contraindicated for use with MAOIs. All patients should be observed carefully for the development of depression with concomitant suicidal tendencies.

Patients 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). Patients 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, patients 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.

Patients 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. Patients taking dopaminergic medications may experience intense gambling urges, increased sexual urges, intense urges to spend money, binge eating, and/or other intense urges, and the inability to control these urges. These urges stopped when the dosage was decreased or the medication discontinued.

A higher risk for melanoma has been reported. Occasionally, dark red, brown, or black color may appear in saliva, urine, or sweat after ingestion of carbidopa and levodopa. Although the color appears to be clinically insignificant, garments may become discolored.^[2],[3],[4]

Patient Teaching & Education: Patients should take their medications at regular intervals as directed. If gastric irritation is experienced, patients may eat food shortly after taking medications, but high-protein foods may impair drug action. Medications may cause increased drowsiness, dizziness, and orthostatic changes. Patients should carefully assess their skin to monitor for new lesions and any abnormality should be reported to the health care provider.

Now let’s take a closer look at the medication grid for carbidopa-levodopa in Table 8.11a.^[5]

Table 8.11a Carbidopa-Levodopa Medication Grid

Class/Subclass	Prototype/Generic	Administration Considerations	Therapeutic Effects	Adverse/Side Effects
Anti-Parkinson’s Agent	carbidopa/levodopa	Avoid high-protein diets due to decreased absorption Monitor for sudden somnolence and increased depression Contraindicated with MAOIs Periodically monitor hepatic, renal, and hematopoietic functions	Slow progression of symptoms of Parkinson’s disease (tremors, rigidity, and mobility issues)	Depression, suicidal ideation, hallucinations, and intense urges with inability to control them Somnolence and fatigue NMS symptoms with dose reductions or when discontinued Dyskinesia Discolored body fluids Hypomobility with long-term use

Selegiline

Selegiline is often used conjunction with carbidopa-levodopa when patients demonstrate a deteriorating response to this treatment. It is helpful to control symptom fluctuations.^[6]

Mechanism of Action: Selegiline inhibits MAO-B, blocking the breakdown of dopamine.^[7]

Indications: Selegiline capsules are indicated as an adjunct in the management of Parkinsonian patients being treated with levodopa/carbidopa who exhibit deterioration in the quality of their response to this therapy. There is no evidence from controlled studies that selegiline has any beneficial effect in the absence of concurrent levodopa therapy.

Nursing Considerations: Large doses of selegiline may inhibit MAO-A that promotes metabolism of tyramine in the GI tract, which can cause a hypertensive crisis.

Side Effects/Adverse Effects: Side effects are dose-dependent, with larger doses posing a hypertensive crisis risk if there is consumption of food or beverages with tyramine.

Patient Teaching & Education: Patients should be advised to avoid foods high in tyramine. Additionally, medications may cause increased drowsiness, dizziness, and orthostatic changes. If patients experience abnormal behaviors such as hallucinations, sexual urges, gambling, etc., this should be reported promptly to the health care provider.

Now let’s take a closer look at the medication grid for selegiline in Table 8.11b.^[8]

Table 8.11b Selegiline Medication Grid

Class/Subclass	Prototype/Generic	Administration Considerations	Therapeutic Effects	Adverse/Side Effects
Anti-Parkinson’s Agent, MAO Type B Inhibitor	selegiline	Avoid food with tyramine if on a large dose (above 10mg/day)	Minimize progression of Parkinson’s disease symptoms	Higher doses increase risk for hypertensive crisis

Amantadine

Amantadine is used in early stages of Parkinson’s disease but can be effective in moderate or advanced stages in reducing tremor and muscle rigidity.^[9]

Mechanism of Action: The exact mechanism of action is unknown. Amantadine is an antiviral drug that acts on dopamine receptors.^[10]

Indications: Amantadine is used for Parkinson’s disease, medication-induced extrapyramidal symptoms, and influenza A.

Nursing Considerations: Use cautiously with renal impairment. This drug may cause suicidal ideation and should not be stopped abruptly or can cause Parkinsonian crisis. Neuroleptic malignant syndrome (NMS) has been reported in association with dose reduction or withdrawal of amantadine therapy.

Side Effects/Adverse Effects: Suicide ideation, congestive heart failure, and peripheral edema can occur. This drug can cause intense gambling urges, increased sexual urges, intense urges to spend money uncontrollably, and other intense urges with an inability to control them. There is an increased risk of melanoma.

Adverse reactions reported most frequently are nausea, dizziness (light-headedness), and insomnia. This drug can also cause anticholinergic side effects, impaired thinking, and orthostatic hypotension.^[11]

Patient Teaching & Education: Patients should take medications as directed and ensure they do not skip or double doses. Medications may cause drowsiness, dizziness, and orthostatic blood pressure changes. Patients should avoid using this medication with OTC cold medications or alcoholic beverages. If patients, family, or caregivers note worsening depression or suicidality, this should be reported immediately to the health care provider.

Now let’s take a closer look at the medication grid for amantadine in Table 8.11c.^[12]

Table 8.11c Amantadine Medication Grid

Class/Subclass	Prototype/Generic	Administration Considerations	Therapeutic Effects	Adverse/Side Effects
Anti-Parkinson Agent, Antiviral	amantadine	Monitor renal function Monitor mental state Assess blood pressure	Improve Parkinson’s disease symptoms	Increased suicidal ideation and urges Congestive heart failure and peripheral edema Neuroleptic malignant syndrome (NMS) when dosage decreased Orthostatic hypotension Nausea, dizziness, and insomnia Anticholinergic side effects