Carbidopa

What is carbidopa?

Carbidopa is used with levodopa to treat Parkinson's disease. Parkinson's disease is believed to be related to low levels of a chemical called dopamine (DOE pa meen) in the brain. Levodopa (Dopar, Larodopa) is turned into dopamine in the body. Carbidopa is used with levodopa to prevent the breakdown (metabolism) of levodopa before it can reach the brain and take effect. Carbidopa is only effective if it is taken with levodopa. It has no effect if it is used alone.

Carbidopa is used with levodopa to treat the stiffness, tremors, spasms, and poor muscle control of Parkinson's disease. These medications are also used to treat the same muscular conditions when they are caused by drugs such as chlorpromazine (Thorazine), fluphenazine (Prolixin), perphenazine (Trilafon), and others.

Carbidopa may also be used for purposes other than those listed in this medication guide.

What is the most important information I should know about carbidopa?

Carbidopa is only used in combination with levodopa. It has no effect if it is used on its own.

What should I discuss with my healthcare provider before taking carbidopa?

Do not take this medication without first talking to your doctor if you have

• taken a monoamine oxidase inhibitor (MAOI) such as isocarboxazid (Marplan), tranylcypromine (Parnate), or phenelzine (Nardil) in the past 2 weeks;

• narrow-angle glaucoma (angle closure glaucoma); or

• malignant melanoma (a type of skin cancer).

Before taking this medication, tell your doctor if you have

• heart disease, high blood pressure, arteriosclerosis, hardening of the arteries, a previous heart attack, or an irregular heartbeat;

• respiratory disease, including asthma and chronic obstructive pulmonary disease (COPD);

• liver disease;
• kidney disease;

• an endocrine (hormonal) disease;

• a stomach or intestinal ulcer;

• wide-angle glaucoma; or

• depression or any other psychiatric disorder.

You may need a dosage adjustment or special monitoring during treatment if you have any of the conditions listed above.

How should I take carbidopa?

Take carbidopa exactly as directed by your doctor. If you do not understand these directions, ask your pharmacist, nurse, or doctor to explain them to you.

Carbidopa must be taken with levodopa to have an effect.

It is important to take carbidopa regularly to get the most benefit.

Your doctor may want you to have blood tests or other medical evaluations during treatment with carbidopa to monitor progress and side effects.

What happens if I miss a dose?

Take the missed dose as soon as you remember. However, if it is almost time for the next dose, skip the missed dose and only take the next regularly scheduled dose. Do not take a double dose of this medication.

What happens if I overdose?

Seek emergency medical attention if an overdose is suspected.

Symptoms of a carbidopa overdose include muscle spasms or weakness, spasms of the eyelid, nausea, vomiting, diarrhea, an irregular heartbeat, confusion, agitation, hallucinations, and unconsciousness.

What should I avoid while taking carbidopa?

Use caution when driving, operating machinery, or performing other hazardous activities. Carbidopa may cause dizziness or drowsiness. If you experience dizziness or drowsiness, avoid these activities.

Carbidopa side effects

Carbidopa alone is not associated with side effects. The following side effects are generally associated with carbidopa and levodopa therapy.

• an allergic reaction (difficulty breathing; closing of the throat; swelling of the lips, tongue, or face; or hives);

• uncontrolled movements of a part of the body;

• seizures;

• persistent nausea, vomiting, or diarrhea;

• an irregular heartbeat or fluttering in your chest;

• unusual changes in mood or behavior; or

• depression or suicidal thoughts.

Other, less serious side effects may be more likely to occur. Continue to take carbidopa and levodopa and talk to your doctor if you experience

• mild nausea, vomiting, or decreased appetite;

• constipation, dry mouth, or blurred vision;

• hand tremor;

• muscle twitches;

• dizziness or drowsiness;

• insomnia, confusion, or nightmares;

• agitation or anxiety;

• darkening of urine or sweat; or

• fatigue.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Carbidopa Dosing Information

Usual Adult Dose for Parkinsonian Tremor:

Initial:
25 mg three to four times a day. Give at the same time with levodopa, at 2% to 25% of the previous or recommended daily dosage of levodopa when taken alone.

In patients already on levodopa, allow 12 hours between the last dose of levodopa and the initiation of therapy with carbidopa and levodopa.

Maximum daily dosage should not exceed 200 mg.

Usual Adult Dose for Neuroleptic Malignant Syndrome:

Case Report:
Carbidopa 25 mg/levodopa 250 mg three times daily via nasogastric tube for 2 days.

Usual Pediatric Dose for GTP-CH Deficiency:

Case Reports:
>1 year:
Initial: 5 mg/kg/day of carbidopa/levodopa, then titrated slowly downward with the aim of maintaining control of extrapyramidal syndrome.

What other drugs will affect carbidopa?

Do not take carbidopa and levodopa if you have taken a monoamine oxidase inhibitor (MAOI) such as isocarboxazid (Marplan), phenelzine (Nardil), or tranylcypromine (Parnate) in the past 14 days.

Antacids may increase the effectiveness of carbidopa and levodopa and lead to side effects. Ask your doctor about the use of antacids.

Before taking carbidopa, tell your doctor if you are taking any of the following medicines:

• a medicine to treat high blood pressure (hypertension);

• a medicine used to treat seizures, such as phenytoin (Dilantin), ethotoin (Peganone), or mephenytoin (Mesantoin);

• papaverine (Pavabid, Cerespan, others);

• pyridoxine or vitamin B6;

• an antidepressant such as amitriptyline (Elavil), doxepin (Sinequan), nortriptyline (Pamelor), desipramine (Norpramin), and amoxapine (Asendin); or

• a medicine used to treat a psychiatric condition (or nausea and vomiting), such as chlorpromazine (Thorazine), fluphenazine (Prolixin), mesoridazine (Serentil), thioridazine (Mellaril), trifluoperazine (Stelazine), and haloperidol (Haldol).

You may not be able to take carbidopa, or you may require a dosage adjustment or special monitoring if you are taking any of the medicines listed above.

Levodopa may interfere with urine tests for sugar and ketones. If you have diabetes and notice changes in urine test results, talk to your doctor before making any changes in your diabetes medication.

Drugs other than those listed here may also interact with carbidopa. Talk to your doctor and pharmacist before taking any prescription or over-the-counter medicines, including vitamins, minerals, and herbal products.

Where can I get more information?

• Your pharmacist can provide more information about carbidopa.

• Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed
• Every effort has been made to ensure that the information provided by Cerner Multum, Inc. ('Multum') is accurate, up-to-date, and complete, but no guarantee is made to that effect. Drug information contained herein may be time sensitive. Multum information has been compiled for use by healthcare practitioners and consumers in the United States and therefore Multum does not warrant that uses outside of the United States are appropriate, unless specifically indicated otherwise. Multum's drug information does not endorse drugs, diagnose patients or recommend therapy. Multum's drug information is an informational resource designed to assist licensed healthcare practitioners in caring for their patients and/or to serve consumers viewing this service as a supplement to, and not a substitute for, the expertise, skill, knowledge and judgment of healthcare practitioners. The absence of a warning for a given drug or drug combination in no way should be construed to indicate that the drug or drug combination is safe, effective or appropriate for any given patient. Multum does not assume any responsibility for any aspect of healthcare administered with the aid of information Multum provides. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the drugs you are taking, check with your doctor, nurse or pharmacist.