Drug information of carbidopa


Carbidopa is used with another medicine called levodopa to treat the symptoms of Parkinson's disease (stiffness, tremors, spasms, poor muscle control). Symptoms of Parkinson's disease may be caused by low levels of a chemical called dopamine (DOE pa meen) in the brain.

Levodopa is converted to dopamine in the brain. Carbidopa helps prevent the breakdown of levodopa before it can reach the brain and take effect.

Carbidopa is only used in combination with levodopa. Carbidopa has no effect when used alone.

Carbidopa is also used with levodopa to treat muscle symptoms similar to Parkinson's disease that are caused by certain drugs such as chlorpromazine (Thorazine), fluphenazine (Prolixin), perphenazine (Trilafon), and others.

Mechanism of effect

Carbidopa is an inhibitor of the DDC which in order, inhibits the peripheral metabolism of levodopa. DDC is very important in the biosynthesis of L-tryptophan to serotonin and the modification of L-DOPA to dopamine.

DDC can be found in the body periphery and in the blood-brain barrier. The action of carbidopa is focused on peripheral DDC as this drug cannot cross the blood-brain barrier


When mixed with levodopa, carbidopa inhibits the peripheral conversion of levodopa to dopamine and the decarboxylation of oxitriptan to serotonin by aromatic L-amino acid decarboxylase. This results in an increased amount of levodopa and oxitriptan available for transport to the central nervous system. Carbidopa also inhibits the metabolism of levodopa in the GI tract, thus, increasing the bioavailability of levodopa.4

The presence of additional units of circulating levodopa can increase the effectiveness of the still functional dopaminergic neurons and it has been shown to alleviate symptoms for a time. The action of carbidopa is very important as levodopa is able to cross the blood-brain barrier while dopamine cannot.8 Hence the administration of carbidopa is essential to prevent the transformation of external levodopa to dopamine before reaching the main action site in the brain.

The coadministration of carbidopa with levodopa has been shown to increase the half-life of levodopa more than 1.5 times while increasing the plasma level and decreasing clearance. The combination therapy has also shown an increase of the recovery of levodopa in urine instead of dopamine which proves a reduced metabolism.



When levodopa/carbidopa is administered orally, 40-70% of the administered dose is absorbed. A maximum concentration of 0.085 mcg/ml was achieved after 143 min with an AUC of 19.28 mcg.min/ml.6

Volume of distribution

The volume of distribution reported for the combination therapy of carbidopa/levodopa is of 3.6 L/kg.7 However, carbidopa is widely distributed in the tissues, except in the brain.12 After one hour, carbidopa is found mainly in the kidney, lungs, small intestine and liver.1

Protein binding

It is widely accepted that the protein binding of carbidopa is 76%. However, more studies are required or the presentation of the source of this information.


There are several metabolites of carbidopa metabolism including 3-(3,4-dihydroxyphenyl)-2-methylpropionic acid, 3-(4-hydroxy-3-methoxyphenyl)-2-methylpropionic acid, 3-(3-hydroxyphenyl)-2-methylpropionic acid, 3-(4-hydroxy-3-methoxyphenyl)-2-methyllactic acid, 3-(3-hydroxyphenyl)-2-methyllactic acid, and 3,4-dihydroxyphenylacetone (1,2)

Half life

The reported half-life of carbidopa is of approximately 107 minutes

Drug indications

This medication is used with a combination levodopa/carbidopa product to treat symptoms of Parkinson's disease or Parkinson-like symptoms (such as shakiness, stiffness, difficulty moving). Carbidopa must be taken together with a drug that contains levodopa to be effective.

Drug contraindications

  • malignant melanoma
  • a type of skin cancer
  • diabetes
  • mental problems from taking the drug
  • psychotic disorder
  • suicidal thoughts
  • depression
  • wide-angle glaucoma
  • closed angle glaucoma
  • a heart attack
  • abnormal heart rhythm
  • a disease of the lung
  • a stomach ulcer
  • an ulcer of the duodenum
  • an ulcer from too much stomach acid
  • liver problems
  • bleeding of the stomach or intestines
  • seizures
  • a type of abnormal movement disorder called dyskinesia
  • an inability to completely empty the bladder


  • Carbidopa/Levodopa

Side effects

  • Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
  • Signs of depression, thoughts of suicide, nervousness, emotional ups and downs, thinking that is not normal, anxiety, or lack of interest in life.
  • Signs of high or low blood pressure like very bad headache or dizziness, passing out, or change in eyesight.
  • Hallucinations (seeing or hearing things that are not there).
  • Feeling confused.
  • Strong urges that are hard to control (such as eating, gambling, sex, or spending money).
  • Black, tarry, or bloody stools.
  • Belly pain.
  • A burning, numbness, or tingling feeling that is not normal.
  • Any unexplained bruising or bleeding.
  • Chest pain or pressure.
  • A heartbeat that does not feel normal.
  • Fever or chills.
  • Sore throat.
  • A skin lump or growth.
  • Change in color or size of a mole.
  • Change in eyesight, eye pain, or very bad eye irritation.
  • Trouble controlling body movements that is new or worse.
  • Shortness of breath.
  • Feeling very tired or weak.

  • 5-hydroxytryptophan
  • droxidopa
  • solriamfetol

Points of recommendation

Before taking this medication, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Pregnancy level

During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.

Breast feeding warning

It is unknown if this medication passes into breast milk. Consult your doctor before breast-feeding.


Related drugs

safinamide , Apomorphine

Drug forms


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