Carbidopa has not been demonstrated to have any overt pharmacodynamic actions in the recommended doses. The only adverse reactions that have been observed have been with concomitant use of carbidopa with other drugs such as levodopa, and with carbidopa-levodopa combination products.

When LODOSYN is administered concomitantly with levodopa or carbidopa-levodopa combination products, the most common adverse reactions have included dyskinesias such as choreiform, dystonic, and other involuntary movements, and nausea. Other adverse reactions reported with LODOSYN when administered concomitantly with levodopa alone or carbidopa-levodopa combination products were psychotic episodes including delusions, hallucinations, and paranoid ideation, depression with or without development of suicidal tendencies, and dementia.

Convulsions also have occurred; however, a causal relationship with concomitant use of LODOSYN and levodopa has not been established.

The following other adverse reactions have been reported with levodopa and carbidopa-levodopa combination products. These same adverse reactions may also occur when LODOSYN is administered with these products.

Body as a Whole: abdominal pain and distress, asthenia, chest pain, fatigue. Cardiovascular: cardiac irregularities, hypertension, myocardial infarction, hypotension including orthostatic hypotension, palpitation, phlebitis, syncope.

Gastrointestinal: anorexia, bruxism, burning sensation of the tongue, constipation, dark saliva, development of duodenal ulcer, diarrhea, dry mouth, dyspepsia, dysphagia, flatulence, gastrointestinal bleeding, gastrointestinal pain, heartburn, hiccups, sialorrhea, taste alterations, vomiting.

Hematologic: hemolytic and non-hemolytic anema, leukopenia, thrombocytopenia, agranulocytosis.

Hypersensitivity: angioedema, urticaria, pruritus, Henoch-Schonlein purpura, bullous lesions (including pemphigus-like reactions).

Metabolic: edema, weight gain, weight loss.

Musculoskeletal: back pain, leg pain, muscle cramps, shoulder pain.

Nervous System/Psychiatric: 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, paresthesia, peripheral neuropathy, somnolence, trismus, activation of latent Horner's syndrome, increased libido.

Respiratory: upper respiratory infection, dyspnea, pharyngeal pain, cough. Skin: flushing, increased sweating, malignant melanoma (see also CONTRAINDICATIONS), rash, alopecia, dark sweat.

Special Senses: oculogyric crises, diplopia, blurred vision, dilated pupils.

Urogenital: dark urine, priapism, urinary frequency, urinary incontinence, urinary retention, urinary tract infection.

Laboratory Tests: abnormalities in alkaline phosphatase, SGOT (AST), SGPT (ALT), lactic dehydrogenase, bilirubin, blood urea nitrogen (BUN), Coombs test; elevated serum glucose; decreased hemoglobin and hematocrit; decreased white blood cell count and serum potassium; increased serum creatinine and uric acid; white blood cells, bacteria and blood in the urine; protein and glucose in the urine.

Miscellaneous: bizarre breathing patterns, faintness, hoarseness, hot flashes, malaise, neuroleptic malignant syndrome, sense of stimulation.

Caution should be exercised when the following drugs are administered concomitantly with LODOSYN (Carbidopa) given with levodopa or carbidopa-levodopa combination products.

Symptomatic postural hypotension has occurred when LODOSYN, given with levodopa or carbidopa-levodopa combination products, was added to the treatment of a patient receiving antihypertensive drugs. Therefore, when therapy with LODOSYN, given with or without levodopa or carbidopa-levodopa combination products, is started, dosage adjustment of the antihypertensive drug may be required.

For patients receiving monoamine oxidase inhibitors, see CONTRAINDICATIONS. Concomitant therapy with selegiline and carbidopa-levodopa may be associated with severe orthostatic hypotension not attributable to carbidopa-levodopa alone (see CONTRAINDICATIONS).

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. In addition, the beneficial effects of levodopa in Parkinson's disease have been reported to be reversed by phenytoin and papaverine. Patients taking these drugs with LODOSYN and levodopa or carbidopa-levodopa combination products should be carefully observed for loss of therapeutic response.

Iron salts may reduce the bioavailability of carbidopa and levodopa. The clinical relevance is unclear.

Although metoclopramide may increase the bioavailability of levodopa by increasing gastric emptying, metoclopramide may also adversely affect disease control by its dopamine receptor antagonistic properties.

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