Carbidopa - Mechanism, side effects with levodopa & dose

Carbidopa is a peripheral decarboxylase inhibitor that inhibits the conversion of levodopa to dopamine. It is administered with carbidopa/levodopa in the treatment of:

  • Idiopathic Parkinson disease
  • Postencephalitic parkinsonism, and
  • Symptomatic parkinsonism following an injury to the nervous system by carbon monoxide and/or manganese intoxication.

Note: Carbidopa alone is ineffective. It reduces the adverse effects associated with levodopa.

Carbidopa Dose in Adults

Use in the treatment of Parkinsonism:

Note: The dose should be carefully titrated. It should be used as 1:10 if the dose exceeds 70 mg/day.

Carbidopa augmentation in patients receiving carbidopa-levodopa:

  • Patients receiving carbidopa/levodopa 10/100:
    • 25 mg daily with first daily dose of carbidopa/levodopa. The dose of carbidopa may be increased to 12.5 or 25 mg if required.
    • The total maximum daily dose should nnot exceed 200 mg/day.
  • Patients receiving carbidopa/levodopa 25/250 or carbidopa/levodopa 25/100:
    • 25 mg with any dose of carbidopa/levodopa throughout the day to a maximum total daily dose of 200 mg/day.

Carbidopa Dose in Childrens

Not applicable

Pregnancy Risk Factor C

  • Parkinsons are a rare occurrence in pregnancy.
  • Therefore, this condition has not been studied in this patient group.
  • Carbidopa can however cross the placental barrier so it should be taken with caution.

Carbidopa can be used during breastfeeding

  • It is unknown whether carbidopa can be found in breastmilk. Nursing mothers should exercise caution when using it.

Carbidopa Dose in Renal Disease:

 The manufacturer has not recommended any dose adjustment.

Carbidopa Dose in Liver Disease:

The manufacturer has not recommended any dose adjustment. 

Side effects of Carbidopa/ Levodopa:

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
    • 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:
  • 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 (e.g. 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 and dystonia
    • Blurred vision
    • Diplopia
    • Mydriasis
    • Oculogyric crisis
  • Renal:
    • Increased blood urea nitrogen
    • Increased serum creatinine
  • Respiratory:
    • Cough
    • Dyspnea
    • Hoarseness
    • Upper respiratory tract infection

Contraindication to Carbidopa include:

  • Allergy reactions to carbidopa and any component of the formulation
  • Use nonselective MAO inhibition therapy in conjunction with or within 14-days.
  • Narrow-angle glaucoma

Warnings and Precautions

  • Depression
    • Be on the lookout for any changes in behavior, depression or suicidal tendencies.
  • Dyskinesias
    • It can cause or exacerbate dyskinesia.
  • Disorders of impulse control:
    • Antiparkinson medication has been linked to compulsive behavior and loss of impulse control, such as pathological gambling, binging, excessive money spending, or hypersexuality.
  • Melanoma
    • As antiparkinson therapy is often associated with melanoma, it is important to monitor the patient regularly for abnormal moles.
  • Psychotic effects
    • It can cause psychotic behavior and hallucinations.
  • Somnolence
    • Without warning, patients may fall asleep suddenly while performing daily activities.
    • Patients who are already taking sleeping pills or sedatives should not use it. __S.17__
    • The drug should not be prescribed to patients who are skilled in tasks or require mental alertness such as operating heavy machinery.

Carbidopa: Drug Interaction

Note: Drug Interaction Categories:

  • Risk Factor C: Monitor When Using Combination
  • Risk Factor D: Consider Treatment Modification
  • Risk Factor X: Avoid Concomitant Use

Risk Factor C (Monitor therapy).

Droxidopa Carbidopa can decrease the therapeutic effects of Droxidopa. Carbidopa can decrease the serum concentrations (or lack thereof) of Droxidopa's active metabolite(s). Carbidopa can increase Droxidopa's serum concentration.
Spiramycin Could cause a decrease in serum Carbidopa concentration. This could decrease the effectiveness and efficiency of levodopa.


  • Clinical features of Parkinson disease
  • CBC
  • Liver function tests
  • Renal function
  • Blood pressure
  • Mental status
  • Clinical features of neuroleptic malignant syndrome if abrupt discontinuation is required.
  • Periodic intraocular pressure in patients with wide-angle glaucoma
  • Periodic skin examinations for melanoma

How to take Carbidopa?

Administer it with meals to decrease gastrointestinal side effects.

Mechanism of action of Carbidopa:

Carbidopa, a peripheral decarboxylase inhibitor, is responsible for the inability to decarboxylate levodopa into dopamine. When taken alone, it has little or no activity. It is not like levodopaIt does not cross the blood brain barrier.This allows for therapeutic brain dopamine concentrations to be maintained with lower doses (levodopa) It also inhibits peripheral conversion of levodopa into dopamine. This reduces peripheral side effects of dopamine such as nausea and vomiting as well cardiac arrhythmias.

International brands of Carbidopa:

  • Lodosyn

Carbidopa Brands in pakistan:

Carbidopa [Tabs 50 mg]



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