Carbidopa is a drug used to treat people with Parkinson’s disease. It is classified as a dopaminergic agent, which means it affects the metabolism of dopamine, a signaling neurotransmitter that helps nerve cells to communicate with each other to coordinate movement. Certain amino acids mimic the dopaminergic effects of carbidopa, but care must be taken not to undermine the effectiveness of this drug. If you take this medication, consult your physician for further guidance about your intake of amino acids.
Carbidopa Pharmacology
Carbidopa is used in the treatment of Parkinson’s disease to prevent the premature metabolism of another drug called levodopa by blocking the activity of an enzyme called aromatic-l-amino acid decarboxylase. This extends the drug’s circulation time in the bloodstream and reduces the risk of side effects, such as nausea and vomiting. It also enables more levodopa to reach it’s target -- the brain. Sold under the trade names Sinemet and Parcopa, carbidopa is actually a combination drug that contains both carbidopa and levodopa. Certain enzymes promote the same dopaminergic effects of carbidopa, either by acting as building blocks for the manufacture of the natural form of levodopa in the body, or by regulating the metabolism of dopamine.
Role of Levodopa
Levodopa is the pure form of an amino acid naturally produced in the human body called L-3,4-dihydroxyphenylalanine, also known as L-dopa. This chemical is used to make dopamine, which is also manufactured in cells in the part of the brain called the substantia nigra. Since the 1960s, levodopa has been the standard treatment for movement disorders associated with Parkinson’s disease, including dystonia and bradykinesia, which cause painful muscle contractions and slowed movements.
Tyrosine
Tyrosine is a non-essential amino acid that cells in the body use to make proteins. It is also used to produce neurotransmitters, including dopamine. Various steps in this process involve other amino acids. It begins with the conversion of an amino acid called phenylalanine into tyrosine, which is then converted into the amino acid L-dopa, or levodopa, and finally into dopamine in the brain. Because of this, you should not take tyrosine supplements while taking carbidopa. You might also need to limit your intake of tyrosine-containing foods, such as poultry, dairy products, soy and certain nuts and seeds, when taking this medication.
Phenylalanine
This is an essential amino acid, meaning you have to get it from dietary sources because your body can’t make it. There is evidence that supplementation with this amino acid may act like carbidopa to help improve movement and speech impairment associated with Parkinson’s disease, but so far this effect has only been demonstrated in animals. Phenylalanine is found in the same kinds of foods as tyrosine and, of course, is a precursor to tyrosine, levodopa and dopamine. A little-known but abundant source of phenylalanine is the artificial sweetener aspartame, and regular use of this product may interfere with the absorption of carbidopa.
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