Carbidopa/Levodopa

Levodopa

Mechanism :

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.

Indication :

• Parkinson’s disease
• Dopa responsive dystonia in children

Contraindications :

Contraindicated in patients with known hypersensitivity to any component of this drug.

Nonselective monoamine oxidase (MAO) inhibitors are contraindicated for use with levodopa or carbidopa-levodopa combination products. These inhibitors must be discontinued at least two weeks prior to initiating therapy with levodopa. Levodopa or carbidopa-levodopa products are contraindicated in patients with narrow-angle glaucoma.

Because levodopa or carbidopa-levodopa products, may activate a malignant melanoma, they should not be used in patients with suspicious, undiagnosed skin lesions or a history of melanoma.

Dosing :

Adverse Effect :

Abdominal pain, asthenia, chest pain, fatigue, hypertension, myocardial infarction, hypotension including orthostatic hypotension, palpitation, syncope, anorexia, bruxism, burning sensation of the tongue, constipation, dark saliva, duodenal ulcer, diarrhea, dry mouth, dyspepsia, dysphagia, flatulence, gastrointestinal bleeding, gastrointestinal pain, heartburn, hiccups, sialorrhea, taste alterations, vomiting, hemolytic and non-hemolytic anemia, leukopenia, thrombocytopenia, agranulocytosis, angioedema, urticaria, pruritus, Henoch-Schonlein purpura, bullous lesions, edema, weight gain, weight loss, back pain, leg pain, muscle cramps, shoulder pain, agitation, anxiety, ataxia, blepharospasm (which may be taken as an early sign of excess dosage; consideration of dosage reduction may be made at this time), bradykinetic episodes (“on-off” phenomenon), confusion, decreased mental acuity, disorientation, euphoria, dizziness, dream abnormalities including nightmares, extrapyramidal disorder, falling, gait abnormalities, headache, increased tremor, insomnia, memory impairment, muscle twitching, nervousness, numbness, paraesthesia, peripheral neuropathy, somnolence, trismus, activation of latent Horner’s syndrome, increased libido, increased sweating, malignant melanoma, oculogyric crises, diplopia, blurred vision, dilated pupils, dark urine, priapism, urinary frequency, urinary incontinence, urinary retention, abnormalities in alkaline phosphatase, AST/ALT, lactic dehydrogenase, bilirubin, blood urea nitrogen (BUN).

Interaction :

Caution should be exercised when the following drugs are administered concomitantly with Carbidopa.
Antihypertensive Drugs: Symptomatic postural hypotension has occurred when levodopa or carbidopa-levodopa combination products was added to the treatment of a patient receiving antihypertensive drugs.
Selegiline: Concomitant therapy with selegiline and carbidopa-levodopa may be associated with severe orthostatic hypotension not attributable to carbidopa-levodopa alone.
Tricyclic Antidepressants: There have been rare reports of adverse reactions, including hypertension and dyskinesia, resulting from the concomitant use of tricyclic antidepressants and carbidopa-levodopa preparations.
Dopamine D2 receptor antagonists (e.g., phenothiazines, butyrophenones, risperidone) and isoniazid: May reduce the therapeutic effects of levodopa.

Phenytoin and Papaverine: In addition, the beneficial effects of levodopa in Parkinson's disease have been reported to be reversed by phenytoin and papaverine.
Iron salts may reduce the bioavailability of carbidopa and levodopa. The clinical relevance is unclear.
Metoclopramide: Although it may increase the bioavailability of levodopa by increasing gastric emptying, metoclopramide may also adversely affect disease control by its dopamine receptor antagonistic properties.

Hepatic Dose :