What is the Difference Between Carbidopa-Levodopa and Ropinirole

The key difference between Carbidopa-Levodopa and Ropinirole is that Carbidopa-Levodopa is a combined medication that increases dopamine levels in the brain by inhibiting aromatic amino acid decarboxylase. At the same time, Ropinirole is a dopamine agonist that directly stimulates dopamine receptors in the brain, mimicking the effects of dopamine.

Parkinson’s disease is a brain disorder that is characterized by uncontrollable movements. As the disease progresses, patients experience difficulty in walking and talking. Managing the symptoms of Parkinson’s disease was primarily associated with carbidopa-levodopa supplementation, which increases dopamine levels in the brain by inhibiting aromatic amino acid decarboxylase. However, the long-term treatments were associated with motor fluctuation and wearing-off phenomena. To improve the carbidopa-levodopa-associated motor fluctuation and wearing-off effect, dopamine agonists such as Ropinirole have been introduced. Ropinirole directly stimulates dopamine receptors in the brain, mimicking the effects of dopamine. The choice between Carbidopa-Levodopa and Ropinirole, or their combination, depends on various factors and should be discussed with a healthcare professional.

CONTENTS

1. Overview and Key Difference
2. What is Carbidopa-Levodopa
3. What is Ropinirole
4. Similarities – Carbidopa-Levodopa and Ropinirole
5. Carbidopa-Levodopa vs Ropinirole in Tabular Form
6. Summary – Carbidopa-Levodopa vs. Ropinirole

What is Carbidopa-Levodopa?

Levodopa, the metabolic precursor of dopamine, is generally combined with aromatic amino acid decarboxylase inhibitors such as carbidopa to manage the symptoms of Parkinson’s disease effectively. Levodopa increases the dopamine level in the brain by crossing the blood-brain barrier. However, upon levodopa supplementation, peripheral dopamine level also increases, resulting in nausea and vomiting. Carbidopa is co-administered to prevent peripheral dopamine activation by inhibiting the aromatic amino acid decarboxylase enzyme. Interestingly, carbidopa does not cross the blood-brain barrier and thereby, does not affect the levodopa converting into dopamine in the brain. In addition, levodopa-related dyskinesias are also prevented by the combination of carbidopa.

Recently, extended-release of formulations of Carbidopa-Levodopa has been produced in addition to the immediate-release version. These extended-release formulas display more favorable pharmacological properties with reduced levodopa-associated fluctuations offering stable levodopa plasma concentration. However, some studies suggest that extended-release formulas are associated with incomplete absorption and delayed clinical benefits.

What is Ropinirole?

Ropinirole belongs to the drug class of non-ergoline dopamine agonists and is primarily used to treat Parkinson’s disease and restless leg syndrome. The mechanism of action of Ropinirole includes the stimulation of dopamine receptors in the brain and improving motor functions of the body. Ropinirole has the highest affinity at the D3 receptors, which is abundant in the limbic area of the body. However, it is believed that the effect of Ropinirole in Parkinson’s disease management is related to the selective stimulation of D2 receptors in the caudate-putamen system in the brain, which affects body movements.

Ropinirole is rapidly absorbed orally and reaches the peak plasma concentration within 1 to 2 hours. Previous studies revealed no food effect associated with the absorption of Ropinirole. The drug is widely distributed in the body, and 40% is bound to plasma protein with a blood-to-plasma ratio of 1:1. Ropinirole is mainly metabolized in the liver, and dephosphorylation and hydroxylation are the main metabolic pathways. The liver mostly clears it, and less than 10% of the administered dose is excreted as the unchanged drug in the urine. Nevertheless, the drug is proven effective in Parkinson’s disease management. However, effects such as carcinogenicity, mutagenesis, and effects on reproduction have been found with Ropinirole.

What are the Similarities Between Carbidopa-Levodopa and Ropinirole?

• Carbidopa-levodopa and Ropinirole are commonly prescribed to manage the symptoms of idiopathic Parkinson’s disease.
• Both medications increase dopamine levels in the brain.
• They alleviate the motor symptoms of Parkinson’s disease, such as tremors, rigidity, and bradykinesia.
• Both drugs improve mobility and overall quality of life for individuals with Parkinson’s disease.

What is the Difference Between Carbidopa-Levodopa and Ropinirole?

Both carbidopa-levodopa and Ropinirole are effective treatment options for controlling the symptoms of Parkinson’s disease. However, there is a distinct difference between carbidopa-levodopa and Ropinirole. Carbidopa-levodopa increases the dopamine level in the brain by inhibiting aromatic amino acid decarboxylase activity. In contrast, ropinirole act as a dopamine agonist that directly stimulates dopamine receptors in the brain, mimicking the effects of dopamine. Carbidopa-levodopa cotreatment is commonly used at the advanced stage of Parkinson’s disease, while Ropinirole is used mainly at the initial stages of the disease.

In addition to using Ropinirole in Parkinson’s disease management, it is also used to treat restless legs syndrome. Prolonged use of carbidopa-levodopa is associated with the development of wearing-off and motor fluctuations, while no such side effects have been identified with Ropinirole.

Below is a summary of the difference between carbidopa-levodopa and Ropinirole in tabular form for side-by-side comparison.

Summary – Carbidopa-Levodopa vs. Ropinirole

Carbidopa-levodopa is a combination medication available in various formulations to increase dopamine levels in the brain by inhibiting the enzyme aromatic amino acid decarboxylase. Carbidopa-levodopa can cause side effects such as nausea and dyskinesias, and prolonged use may lead to wearing-off and motor fluctuations. In contrast, Ropinirole is a dopamine agonist that directly stimulates dopamine receptors in the brain. It is primarily used in the early stages of Parkinson’s disease and is also approved for treating restless legs syndrome. Ropinirole has a slower onset of action than carbidopa-levodopa but has a lower risk of causing wearing-off and motor fluctuations. Thus, this is the summary of the difference between carbidopa-levodopa and Ropinirole. The choice between carbidopa-levodopa and Ropinirole, or their combination, depends on various factors and should be discussed with a healthcare professional.

Reference:

1. Im, Joo-Hyuk, et al. “Ropinirole as an Adjunct to Levodopa in the Treatment of Parkinson’s Disease.” Journal of Neurology, vol. 250, no. 1, 2003, pp. 90–96.
2. Jost, Wolfgang H., and Dieter Angersbach. “Ropinirole, a Non-Ergoline Dopamine Agonist.” CNS Drug Reviews, vol. 11, no. 3, 2006, pp. 253–272.

Image Courtesy:

1. “Medicationlevodopa” By Revion101 – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Ropinirole Structural Formulae” By Jü – Own work (Public Domain) via Commons Wikimedia