Parkinsonism:
Note: For patients receiving carbidopa/levodopa therapy, a carbidopa dose ≥75 mg/day may be necessary to decrease the risk of adverse effects from peripheral dopamine (Hoehn 1980; Kaakkola 1985).
Carbidopa augmentation in patients receiving carbidopa-levodopa:
Patients receiving carbidopa/levodopa 10/100: Oral: 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: Oral: 25 mg with any dose of carbidopa/levodopa throughout the day; maximum: 200 mg/day (including from carbidopa/levodopa)
Discontinuation of therapy: Discontinuation of carbidopa/levodopa therapy may result in neuroleptic malignant-like syndrome (Grimes 2019). Avoid sudden discontinuation or rapid dose reduction; some experts recommend a gradual taper over several weeks or more (Oliver 2021).
Dosage adjustment for concomitant therapy: Significant drug interactions exist, requiring dose/frequency adjustment or avoidance. Consult drug interactions database for more information.
Refer to adult dosing.
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
Yes
Administer with meals to decrease GI upset.
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; carbidopa has no effect without levodopa.
The Institute for Safe Medication Practices (ISMP) includes this medication among its list of drugs that have a heightened risk of causing significant patient harm when used in error.
Lodosyn [US] may be confused with Lidosen brand name for lidocaine [Italy]
The following adverse drug reactions are derived from product labeling unless otherwise specified. Adverse reactions are associated with concomitant administration with levodopa in adults.
Postmarketing:
Cardiovascular: Acute myocardial infarction, chest pain, edema, flushing, hypertension, hypotension, orthostatic hypotension, palpitations, phlebitis, syncope
Dermatologic: Alopecia, bullous rash (including bullous pemphigoid), dark sweat, diaphoresis, malignant melanoma, pruritus, skin rash, urticaria
Endocrine & metabolic: Abnormal lactate dehydrogenase, decreased serum potassium, hot flash, hyponatremia (Shihabudheen 2020), increased libido (including hypersexuality), increased serum glucose, increased uric acid, pyridoxine deficiency (Wise 2022), weight gain, weight loss
Gastrointestinal: Abdominal distress, abdominal pain, anorexia, bruxism, constipation, dark saliva, diarrhea, duodenal ulcer, dysgeusia, dyspepsia, dysphagia, flatulence, gastrointestinal hemorrhage, gastrointestinal pain, glossopyrosis, heartburn, hiccups (Shihabudheen 2020), nausea, sialorrhea, sore throat, vomiting, xerostomia
Genitourinary: Bacteriuria, dark urine, glycosuria, hematuria, priapism, proteinuria, pyuria, urinary frequency, urinary incontinence, urinary retention, urinary tract infection
Hematologic & oncologic: Abnormal Coombs' test, agranulocytosis, anemia, decreased hematocrit, decreased hemoglobin, hemolytic anemia (Bernstein 1979), Henoch-Schonlein purpura (Niedermaier 1997), leukocytosis, leukopenia, thrombocytopenia
Hepatic: Abnormal alanine aminotransferase, abnormal aspartate transaminase, abnormal bilirubin levels, alkaline phosphatase abnormal
Hypersensitivity: Angioedema
Nervous system: Abnormal dreams (including nightmares), aggressive behavior, agitation, asthenia, confusion, dementia, depression (including depression with suicidal tendencies) (Ayobello 2019), disorientation, dizziness, drowsiness, fatigue, headache, impulse control disorder (including pathological gambling), insomnia, malaise, neuroleptic malignant syndrome (Perry 2012), on-off phenomenon (Raja 2020), paresthesia, psychosis (including delusion, hallucination, paranoid ideation) (Hinkle 2018), sense of stimulation
Neuromuscular & skeletal: Back pain, dyskinesia (including choreiform movements, dystonic reaction, and other involuntary body movements), lower leg pain, muscle cramps, shoulder pain
Ophthalmic: Blurred vision, diplopia, mydriasis, oculogyric crisis
Renal: Increased blood urea nitrogen, increased serum creatinine
Respiratory: Cough, dyspnea, hoarseness, irregular breathing, upper respiratory tract infection
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
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.
• 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.
None known.
Note: Interacting drugs may not be individually listed below if they are part of a group interaction (eg, individual drugs within “CYP3A4 Inducers [Strong]” are NOT listed). For a complete list of drug interactions by individual drug name and detailed management recommendations, use the Lexicomp drug interactions program by clicking on the “Launch drug interactions program” link above.
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. Risk C: Monitor therapy
Reserpine: Carbidopa may enhance the hypotensive effect of Reserpine. Reserpine may diminish the therapeutic effect of Carbidopa. Risk X: Avoid combination
Spiramycin: May decrease the serum concentration of Carbidopa. And thus may decrease the effectiveness of levodopa. Risk C: Monitor therapy
Tetrabenazine: May diminish the therapeutic effect of Carbidopa. Risk X: Avoid combination
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.
It is not known if carbidopa is present in breast milk. Due to the potential for serious adverse reactions in the breastfeeding infant, the manufacturer recommends a decision be made whether to discontinue breastfeeding or to discontinue the drug, taking into account the importance of treatment to the mother.
May be taken with meals to decrease GI upset.
CBC, LFTs, renal function; BP, 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).
Carbidopa is a decarboxylase inhibitor with little or no pharmacological activity when given alone in usual doses. Unlike levodopa, carbidopa does not cross the blood-brain barrier and only inhibits the decarboxylation of peripheral levodopa to dopamine. Coadministration of carbidopa with levodopa allows for higher central nervous system concentrations of dopamine with lower doses of levodopa. Reduced peripheral formation of dopamine also reduces peripheral adverse reactions, including nausea and vomiting.
Distribution: Does not cross the blood-brain barrier
Tablets (Carbidopa Oral)
25 mg (per each): $1.75 - $21.85
Tablets (Lodosyn Oral)
25 mg (per each): $35.50
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