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Medically reviewed by Last updated on May 22, 2023.


(kar bi DOE pa)

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Tablet, Oral:

Lodosyn: 25 mg [scored; contains fd&c yellow #6 (sunset yellow)]

Generic: 25 mg

Brand Names: U.S.

  • Lodosyn

Pharmacologic Category

  • Anti-Parkinson Agent, Decarboxylase Inhibitor


Carbidopa is a peripheral decarboxylase inhibitor with little or no pharmacological activity when given alone in usual doses. It inhibits the peripheral decarboxylation of levodopa to dopamine; and as it does not cross the blood-brain barrier, unlike levodopa, effective brain concentrations of dopamine are produced with lower doses of levodopa. At the same time, reduced peripheral formation of dopamine reduces peripheral side-effects, notably nausea and vomiting, and cardiac arrhythmias, although the dyskinesias and adverse mental effects associated with levodopa therapy tend to develop earlier.


Does not cross the blood-brain barrier

Use: Labeled Indications

Parkinsonism: Given with carbidopa/levodopa in the treatment of idiopathic Parkinson disease, postencephalitic parkinsonism, and symptomatic parkinsonism, which may follow injury to the nervous system by carbon monoxide and/or manganese intoxication.

Note: Administration of carbidopa allows use of a lower dosage of levodopa, more rapid titration, and a decrease in nausea and vomiting associated with levodopa; use with carbidopa/levodopa in patients requiring additional carbidopa; has no effect without levodopa.


Hypersensitivity to carbidopa or any component of the formulation; use of nonselective MAO inhibitor therapy with or within prior 14 days (however, may be administered concomitantly with the manufacturer's recommended dose of an MAO inhibitor with selectivity for MAO type B); narrow-angle glaucoma

Dosing: Adult

Parkinsonism: Oral: Note: Optimal daily dosage determined by careful titration; generally if carbidopa is ≥70 mg/day, a 1:10 proportion of carbidopa:levodopa provides the most patient response.

Carbidopa augmentation in patients receiving carbidopa-levodopa:

Patients receiving carbidopa/levodopa 10/100: 25 mg daily with first daily dose of carbidopa/levodopa; if necessary, 12.5 to 25 mg may be given with each subsequent dose of carbidopa/levodopa; maximum: 200 mg/day (including from carbidopa/levodopa)

Patients receiving carbidopa/levodopa 25/250 or carbidopa/levodopa 25/100: 25 mg with any dose of carbidopa/levodopa throughout the day; maximum: 200 mg/day (including from carbidopa/levodopa)

Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.

Dosing: Geriatric

Refer to adult dosing.


Administer with meals to decrease GI upset.

Dietary Considerations

May be taken with meals to decrease GI upset.


Store at room temperature of 25°C (77°F); excursions permitted to 15°C to 30°C (59°F to 86°F).

Drug Interactions

Droxidopa: Carbidopa may diminish the therapeutic effect of Droxidopa. Carbidopa may decrease serum concentrations of the active metabolite(s) of Droxidopa. Carbidopa may increase the serum concentration of Droxidopa. Monitor therapy

Spiramycin: May decrease the serum concentration of Carbidopa. And thus may decrease the effectiveness of levodopa. Monitor therapy

Test Interactions

False-positive reaction for urinary glucose with Clinitest®; false-negative reaction using Clinistix®; false-positive urine ketones with Acetest®, Ketostix®, Labstix®

Adverse Reactions

The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified. Adverse reactions are associated with concomitant administration with levodopa.

Cardiovascular: Cardiac arrhythmia, chest pain, edema, flushing, hypertension, hypotension, myocardial infarction, orthostatic hypotension, palpitation, phlebitis, syncope

Central nervous system: Abnormal dreams, abnormal gait, agitation, anxiety, ataxia, confusion, decreased mental acuity, delusions, dementia, depression (with or without suicidal tendencies), disorientation, dizziness, drowsiness, euphoria, extrapyramidal reaction, falling, fatigue, glossopyrosis, hallucination, headache, Horner's syndrome, impulse control disorder, insomnia, malaise, memory impairment, nervousness, neuroleptic malignant syndrome, nightmares, numbness, on-off phenomenon, paranoia, paresthesia, pathological gambling, peripheral neuropathy, psychosis, seizure (causal relationship not established), trismus

Dermatologic: Alopecia, bulla, diaphoresis, discoloration of sweat, skin rash

Endocrine & metabolic: Abnormal lactate dehydrogenase, glycosuria, hot flash, hyperglycemia, hypokalemia, increased libido (including hypersexuality), increased uric acid, weight changes

Gastrointestinal: Abdominal distress, abdominal pain, anorexia, bruxism, constipation, diarrhea, discoloration of saliva, duodenal ulcer, dysgeusia, dyspepsia, dysphagia, flatulence, gastrointestinal hemorrhage, heartburn, hiccups, nausea, sialorrhea, sore throat, vomiting, xerostomia

Genitourinary: Priapism, proteinuria, urinary frequency, urinary incontinence, urinary retention, urinary tract infection, urine discoloration

Hematologic & oncologic: Abnormal Coombs' test, agranulocytosis, anemia, decreased hematocrit, decreased hemoglobin, hemolytic anemia, leukopenia, malignant melanoma, thrombocytopenia

Hepatic: Abnormal alanine aminotransferase, abnormal alkaline phosphatase, abnormal aspartate transaminase, abnormal bilirubin levels, abnormal lactate dehydrogenase

Hypersensitivity: Angioedema, hypersensitivity reaction (bulla, IgA vasculitis, pruritus, urticaria)

Neuromuscular & skeletal: Back pain, dyskinesia (including choreiform, dystonic, and other involuntary movements), leg pain, muscle cramps, muscle twitching, shoulder pain, tremor, weakness

Ophthalmic: Blepharospasm, blurred vision, diplopia, mydriasis, oculogyric crisis (may be associated with acute dystonic reactions)

Renal: Increased blood urea nitrogen, increased serum creatinine

Respiratory: Cough, dyspnea, hoarseness, upper respiratory tract infection


Concerns related to adverse effects:

• Depression: Observe patients closely for development of depression with concomitant suicidal tendencies.

• Dyskinesias: May cause or exacerbate dyskinesias.

• Impulse control disorders: Antiparkinson therapy has been associated with compulsive behaviors and/or loss of impulse control, which has manifested as pathological gambling, libido increases (hypersexuality), urges to spend money uncontrollably, and/or binge eating. Dose reduction or discontinuation of therapy has been reported to reverse these behaviors in some, but not all cases.

• Melanoma: Risk for melanoma development is increased in Parkinson disease patients; drug causation or factors contributing to risk have not been established. Patients should be monitored closely and periodic skin examinations should be performed.

• Psychotic effects: May cause hallucinations and psychotic-like behavior.

• Somnolence: Patients have reported falling asleep while engaging in activities of daily living; this has been reported to occur without significant warning signs. Monitor for daytime somnolence or preexisting sleep disorder; caution with concomitant sedating medication; consider discontinuing if significant daytime sleepiness or episodes of falling asleep occur. Patients must be cautioned about performing tasks which require mental alertness (eg, operating machinery, driving).

Disease-related concerns:

• Psychotic disorders: Avoid use in patients with major psychotic disorder.

Other warnings/precautions:

• Appropriate use: Carbidopa has no antiparkinsonian activity when administered alone; must administer with carbidopa/levodopa. When administering to carbidopa-naive patients, administer carbidopa and carbidopa/levodopa at the same time; allow at least 12 hours to elapse between the last dose of carbidopa/levodopa and initiation of carbidopa.

• Discontinuation of therapy: Abrupt withdrawal or discontinuation of carbidopa/levodopa been associated with a syndrome resembling neuroleptic malignant syndrome (NMS).

Monitoring Parameters

Signs and symptoms of Parkinson disease; CBC, liver function tests, renal function; blood pressure, mental status; signs and symptoms of neuroleptic malignant syndrome if abrupt discontinuation required (as with surgery); periodic intraocular pressure (in patients with wide-angle glaucoma); periodic skin examinations

Pregnancy Considerations

Carbidopa can be detected in the umbilical cord but absorption in fetal tissue is minimal (Merchant 1995). The incidence of Parkinson disease in pregnancy is relatively rare and information related to the use of carbidopa in pregnant women is limited to use with other agents. Refer to the carbidopa and levodopa monograph for additional information.

Patient Education

What is this drug used for?

• It is used to treat Parkinson disease.

• It is used to treat signs like Parkinson disease caused by other health problems.

• It may be given to you for other reasons. Talk with the doctor.

• This drug needs to be taken with another drug that has levodopa in it. Be sure you know about the warnings, benefits, and risks of the other drug. Talk with your doctor if you have questions or concerns.

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

• Dry mouth

• Diarrhea

• Stomach pain

• Upset stomach

• Throwing up

• Feeling sleepy, tired, or weak

• Trouble sleeping

• Gas

• Heartburn

• Hiccups

• Weight gain

• Weight loss

• Common cold symptoms

• Back pain

• Pain in arms or legs

• Muscle cramps

• Flushing

• Sweating a lot

• Hair loss

• Hot flashes

• Nightmares

• Change in taste

• Constipation

• Not hungry

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

• Depression like thoughts of suicide, anxiety, agitation, irritability, panic attacks, mood changes, behavioral changes, or confusion

• Behavioral changes

• Sensing things that seem real but are not

• Strong urges that are hard to control (such as eating, gambling, sex, or spending money)

• Urinary tract infection like blood in your urine, burning or painful urination, passing a lot of urine, fever, lower abdominal pain, or pelvic pain

• Falling asleep during activities like driving, eating, or talking or feeling very sleepy

• Severe headache

• Abnormal heartbeat

• Throwing up blood

• Black, tarry, or bloody stools

• Burning or numbness feeling

• Bruising

• Bleeding

• Trouble controlling body movements that is new or worse

• Teeth grinding

• Shortness of breath

• Severe loss of strength and energy

• Swelling

• Severe dizziness

• Passing out

• Chest pain

• Chills

• Sore throat

• Skin lump or growth

• Mole changes

• Change in how much urine is passed

• Erection that lasts more than 4 hours

• Vision changes

• 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.

Note: This is not a comprehensive list of all side effects. Talk to your doctor if you have questions.

Consumer Information Use and Disclaimer: This information should not be used to decide whether or not to take this medicine or any other medicine. Only the healthcare provider has the knowledge and training to decide which medicines are right for a specific patient. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a limited summary of general information about the medicine's uses from the patient education leaflet and is not intended to be comprehensive. This limited summary does NOT include all information available about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this medicine. This information is not intended to provide medical advice, diagnosis or treatment and does not replace information you receive from the healthcare provider. For a more detailed summary of information about the risks and benefits of using this medicine, please speak with your healthcare provider and review the entire patient education leaflet.

Frequently asked questions

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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.