Carbidopa

Carbidopa
Adult Indications & Dosage
Pediatric Indications & Dosage
Contraindications
Warnings & Precautions
Adverse Reactions
Drug Interactions
Use in Specific Populations
Administration & Monitoring
Overdosage
Pharmacology
Clinical Studies
How Supplied
Images
Patient Counseling Information
Precautions with Alcohol
Brand Names
Look-Alike Names

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Anusha Vege, M.B.B.S. [2]

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Overview

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Adult Indications and Dosage

FDA-Labeled Indications and Dosage (Adult)

Carbidopa Tablets are indicated for use with carbidopa-levodopa or with levodopa in the treatment of the symptoms of idiopathic Parkinson’s disease (paralysis agitans), postencephalitic parkinsonism, and symptomatic parkinsonism, which may follow injury to the nervous system by carbon monoxide intoxication and/or manganese intoxication.

Carbidopa is for use with carbidopa-levodopa in patients for whom the dosage of carbidopa-levodopa provides less than adequate daily dosage (usually 70 mg daily) of carbidopa.

Carbidopa is for use with levodopa in the occasional patient whose dosage requirement of carbidopa and levodopa necessitates separate titration of each medication Carbidopa is used with carbidopa-levodopa or with levodopa to permit the administration of lower doses of levodopa with reduced nausea and vomiting, more rapid dosage titration, and with a somewhat smoother response. However, patients with markedly irregular (“on-off”) responses to levodopa have not been shown to benefit from the addition of carbidopa.

Since carbidopa prevents the reversal of levodopa effects caused by pyridoxine, supplemental pyridoxine (vitamin B6), can be given to patients when they are receiving carbidopa and levodopa concomitantly or as carbidopa-levodopa.

Although the administration of Carbidopa permits control of parkinsonism and Parkinson’s disease with much lower doses of levodopa, there is no conclusive evidence at present that this is beneficial other than in reducing nausea and vomiting, permitting more rapid titration, and providing a somewhat smoother response to levodopa.

Certain patients who responded poorly to levodopa alone have improved when carbidopa and levodopa were given concurrently. This was most likely due to decreased peripheral decarboxylation of levodopa rather than to a primary effect of carbidopa on the peripheral nervous system. Carbidopa has not been shown to enhance the intrinsic efficacy of levodopa.

In deciding whether to give Carbidopa with carbidopa-levodopa or with levodopa to patients who have nausea and/or vomiting, the physician should be aware that, while many patients may be expected to improve, some may not. Since one cannot predict which patients are likely to improve, this can only be determined by a trial of therapy. It should be further noted that in controlled trials comparing carbidopa and levodopa with levodopa alone, about half the patients with nausea and/or vomiting on levodopa alone improved spontaneously despite being retained on the same dose of levodopa during the controlled portion of the trial.

Off-Label Use and Dosage (Adult)

Guideline-Supported Use

There is limited information regarding Off-Label Guideline-Supported Use of Carbidopa in adult patients.

Non–Guideline-Supported Use

There is limited information regarding Off-Label Non–Guideline-Supported Use of Carbidopa in adult patients.

Pediatric Indications and Dosage

FDA-Labeled Indications and Dosage (Pediatric)

There is limited information regarding Carbidopa FDA-Labeled Indications and Dosage (Pediatric) in the drug label.

Off-Label Use and Dosage (Pediatric)

Guideline-Supported Use

There is limited information regarding Off-Label Guideline-Supported Use of Carbidopa in pediatric patients.

Non–Guideline-Supported Use

There is limited information regarding Off-Label Non–Guideline-Supported Use of Carbidopa in pediatric patients.

Contraindications

There is limited information regarding Carbidopa Contraindications in the drug label.

Warnings

There is limited information regarding Carbidopa Warnings' in the drug label.

Adverse Reactions

Clinical Trials Experience

There is limited information regarding Carbidopa Clinical Trials Experience in the drug label.

Postmarketing Experience

There is limited information regarding Carbidopa Postmarketing Experience in the drug label.

Drug Interactions

There is limited information regarding Carbidopa Drug Interactions in the drug label.

Use in Specific Populations

Pregnancy

Pregnancy Category (FDA): There is no FDA guidance on usage of Carbidopa in women who are pregnant.
Pregnancy Category (AUS): There is no Australian Drug Evaluation Committee (ADEC) guidance on usage of Carbidopa in women who are pregnant.

Labor and Delivery

There is no FDA guidance on use of Carbidopa during labor and delivery.

Nursing Mothers

There is no FDA guidance on the use of Carbidopa in women who are nursing.

Pediatric Use

There is no FDA guidance on the use of Carbidopa in pediatric settings.

Geriatic Use

There is no FDA guidance on the use of Carbidopa in geriatric settings.

Gender

There is no FDA guidance on the use of Carbidopa with respect to specific gender populations.

Race

There is no FDA guidance on the use of Carbidopa with respect to specific racial populations.

Renal Impairment

There is no FDA guidance on the use of Carbidopa in patients with renal impairment.

Hepatic Impairment

There is no FDA guidance on the use of Carbidopa in patients with hepatic impairment.

Females of Reproductive Potential and Males

There is no FDA guidance on the use of Carbidopa in women of reproductive potentials and males.

Immunocompromised Patients

There is no FDA guidance one the use of Carbidopa in patients who are immunocompromised.

Administration and Monitoring

Administration

There is limited information regarding Carbidopa Administration in the drug label.

Monitoring

There is limited information regarding Carbidopa Monitoring in the drug label.

IV Compatibility

There is limited information regarding the compatibility of Carbidopa and IV administrations.

Overdosage

There is limited information regarding Carbidopa overdosage. If you suspect drug poisoning or overdose, please contact the National Poison Help hotline (1-800-222-1222) immediately.

Pharmacology

There is limited information regarding Carbidopa Pharmacology in the drug label.

Mechanism of Action

Mechanism of Action

Current evidence indicates that symptoms of Parkinson's disease are related to depletion of dopamine in the corpus striatum. Administration of dopamine is ineffective in the treatment of Parkinson's disease apparently because it does not cross the blood-brain barrier. However, levodopa, the metabolic precursor of dopamine, does cross the blood-brain barrier, and presumably is converted to dopamine in the brain. This is thought to be the mechanism whereby levodopa relieves symptoms of Parkinson's disease.

Structure

There is limited information regarding Carbidopa Structure in the drug label.

Pharmacodynamics

Pharmacodynamics

When levodopa is administered orally it is rapidly decarboxylated to dopamine in extracerebral tissues so that only a small portion of a given dose is transported unchanged to the central nervous system. For this reason, large doses of levodopa are required for adequate therapeutic effect and these may often be accompanied by nausea and other adverse reactions, some of which are attributable to dopamine formed in extracerebral tissues.

The incidence of levodopa-induced nausea and vomiting is less when Carbidopa is used with levodopa than when levodopa is used without Carbidopa. In many patients this reduction in nausea and vomiting will permit more rapid dosage titration.

Carbidopa inhibits decarboxylation of peripheral levodopa. Carbidopa has not been demonstrated to have any overt pharmacodynamic actions in the recommended doses. It does not appear to cross the blood-brain barrier readily and does not affect the metabolism of levodopa within the central nervous system at doses of carbidopa that are recommended for maximum effective inhibition of peripheral decarboxylation of levodopa.

Since its decarboxylase-inhibiting activity is limited primarily to extracerebral tissues, administration of carbidopa with levodopa makes more levodopa available for transport to the brain. However, since levodopa and carbidopa compete with certain amino acids for transport across the gut wall, the absorption of levodopa and carbidopa may be impaired in some patients on a high protein diet.

Pharmacokinetics

Pharmacokinetics

Carbidopa reduces the amount of levodopa required to produce a given response by about 75% and, when administered with levodopa, increases both plasma levels and the plasma half-life of levodopa, and decreases plasma and urinary dopamine and homovanillic acid.

In clinical pharmacologic studies, simultaneous administration of separate tablets of carbidopa and levodopa produced greater urinary excretion of levodopa in proportion to the excretion of dopamine when compared to the two drugs administered at separate times.

Supplemental pyridoxine (vitamin B6) can be given to patients when they are receiving carbidopa and levodopa concomitantly or the fixed combination carbidopa-levodopa or carbidopa-levodopa extended release. Previous reports in the medical literature cautioned that high doses of vitamin B6 should not be taken by patients on levodopa therapy alone because exogenously administered pyridoxine would enhance the metabolism of levodopa to dopamine. The introduction of carbidopa to levodopa therapy, which inhibits the peripheral decarboxylation of levodopa to dopamine, counteracts the metabolic-enhancing effect of pyridoxine.

Carbidopa is combined with levodopa in carbidopa-levodopa and carbidopa-levodopa extended release tablets.

Nonclinical Toxicology

There is limited information regarding Carbidopa Nonclinical Toxicology in the drug label.

Clinical Studies

There is limited information regarding Carbidopa Clinical Studies in the drug label.

How Supplied

There is limited information regarding Carbidopa How Supplied in the drug label.

Storage

There is limited information regarding Carbidopa Storage in the drug label.

Images

Drug Images

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Package and Label Display Panel

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Patient Counseling Information

There is limited information regarding Carbidopa Patient Counseling Information in the drug label.

Precautions with Alcohol

Alcohol-Carbidopa interaction has not been established. Talk to your doctor about the effects of taking alcohol with this medication.

Brand Names

There is limited information regarding Carbidopa Brand Names in the drug label.

Look-Alike Drug Names

There is limited information regarding Carbidopa Look-Alike Drug Names in the drug label.

Drug Shortage Status

Price

References

The contents of this FDA label are provided by the National Library of Medicine.