What Is Carbidopa/Levodopa Therapy?

The combination of levodopa and carbidopa is a treatment used for Parkinson’s disease (PD). Levodopa/carbidopa is the most effective treatment available for the motor symptoms of PD. Levodopa was first discovered as a treatment for Parkinson’s disease more than 50 years ago.^1-4

How does it work?

Dopamine is a neurotransmitter (chemical messenger) with many jobs. Dopamine is responsible for producing smooth, purposeful movement. PD damages the neurons in the brain that make dopamine. This causes the motor symptoms of PD. This includes symptoms like:^1-4

• Resting tremor (a tremor or shaking that occurs when a body part is at rest)
• Bradykinesia (gradual loss and slowing down of spontaneous movement)
• Rigidity (stiffness or feeling of tension in the muscles)
• Postural instability (impaired balance)

These motor symptoms are related to the loss of dopamine in the brain. By the time Parkinson's symptoms appear, about 60 to 80 percent of the nerves in the brain that make dopamine have been damaged or destroyed.^1-4

Dopamine cannot enter our brains. This means that dopamine by itself cannot work as a treatment for PD. However, levodopa can enter the brain. Levodopa is a building block our bodies can use to make dopamine. Levodopa is converted to dopamine in the brain. The influx of dopamine created by levodopa helps treat the motor symptoms of PD.^1-4

Adding carbidopa prevents levodopa from being converted into dopamine before it is able to enter the brain. This allows more of the drug to get to the brain. This also means that lower doses of levodopa can be given. The addition of carbidopa also reduces the risk of some side effects, like nausea or vomiting.^1,2

Different brands available

Several versions of carbidopa/levodopa treatments are available to treat Parkinson's, including:^1,5

• Dhivy^TM (carbidopa levodopa) tablet
• Duopa^® (carbidopa levodopa) enteral suspension
• Inbrija^® (levodopa) inhalation powder
• Parcopa^® (carbidopa levodopa) orally disintegrating tablet
• Rytary^® (carbidopa levodopa ER) capsule
• Sinemet^® (carbidopa levodopa) tablet
• Sinemet^® CR (carbidopa levodopa ER) tablet
• Stalevo^® (carbidopa/levodopa/entacapone) tablet

There are different dosages for each of these treatments. People may be prescribed different amounts at different points in their disease to manage their symptoms.^1,5

• Dhivy^TM - A tablet that can be broken into smaller pieces.
• Duopa^® – A gel delivered via a tube directly into the intestines by a pump for up to 16 hours. It requires a procedure to make a small hole (stoma) in the stomach wall. It is an option for people who still have symptoms while taking pills for PD.
• Inbrija^® – Levodopa that is inhaled when someone has an "off" period.
• Rytary^® – A capsule that releases slowly.
• Parcopa^® – A pill that dissolves on the tongue. No water is required to take Parcopa.
• Sinemet^® and Sinemet^® – A tablet. Sinemet CR is no longer made, but some generic forms are.
• Stalevo^® – A tablet that includes carbidopa, levodopa, and entacapone.

What are the possible side effects?

The most common side effects of carbidopa/levodopa therapy include:¹

• Nausea and vomiting
• Falling blood pressure that happens upon standing
• Worsening glaucoma (a condition that damages the eye)
• Dyskinesia (sudden, involuntary movement)
• Hallucination (seeing things that are not real)
• Psychosis
• Low blood pressure
• Confusion
• Dry mouth
• Dizziness

Dyskinesias are sudden, involuntary movements. These are called motor symptoms and are a common side effect of taking levadopa long-term. Dyskinesias can impact quality of life. The severity of these symptoms due to levodopa varies. The risk of dyskinesia is higher in early-onset Parkinson's. Drugs may be added or changed to prevent motor symptoms. Deep brain stimulation may also be an option.^3,6

You should not stop taking carbidopa/levodopa suddenly without talking to your doctor. People who stop taking these drugs suddenly may develop a serious syndrome that causes fever, rigidity, dyskinesias, and confusion.⁷

These are not all the possible side effects of carbidopa/levodopa treatments. Talk to your doctor about what to expect when taking these drugs. You should also call your doctor if you have any changes that concern you when taking carbidopa/levodopa therapy.

For some people, their PD symptoms are not well controlled by carbidopa/levodopa. In this case, more treatments may be added. People may also switch to other drugs.

Additional therapy

Besides COMT inhibitors, there are several different types of treatment for the symptoms of PD, including:

• Dopamine agonists
• Anticholinergics
• MAO-B inhibitors
• COMT inhibitors
• Surgery for deep brain stimulation

Each person with PD experiences a unique set of symptoms and progression of the disease. Treatments are based on the person's symptoms and how they respond to different drugs.