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Side effects that occur frequently in patients receiving Sinemet are those due to the central neuropharmacologic activity of dopamine. These reactions usually can be diminished by dosage reduction. The most common side effects are dyskinesias, including choreiform, dystonic and other involuntary movements. Muscle twitching and blepharospasm may be taken as early signs to consider dosage reduction.
Other serious side effects are mental changes, including paranoid ideation and psychotic episodes; depression with or without development of suicidal tendencies; and dementia. A common but less serious side effect is nausea.
Less frequent side effects are cardiac irregularities and/or palpitation, orthostatic hypotensive episodes, bradykinetic episodes (the "on-off" phenomenon), anorexia, vomiting, dizziness and somnolence.
Gastrointestinal bleeding, development of duodenal ulcer, hypertension, phlebitis, leukopenia, hemolytic and nonhemolytic anemia, thrombocytopenia, agranulocytosis, chest pain, dyspnea and paresthesia have occurred rarely.
Occasionally, convulsions have occurred; however, a causal relationship with Sinemet has not been established.
Laboratory Tests: Transient abnormalities in laboratory tests which, however, have not been associated with clinical evidence of disease, include elevations of blood urea nitrogen, SGOT, SGPT, LDH, bilirubin, alkaline phosphatase or protein-bound iodine.
Decreased hemoglobin and hematocrit, elevated serum glucose, and white blood cells, bacteria and blood in the urine have been reported.
Commonly, levels of blood urea nitrogen, creatinine and uric acid are lower during administration of Sinemet than with levodopa.
Positive Coombs' tests have been reported both with Sinemet and with levodopa alone, but hemolytic anemia is extremely rare.
Sinemet may cause a false-positive reaction for urinary ketone bodies when a test tape is used for determination of ketonuria. This reaction will not be altered by boiling the urine specimen. False-negative tests may result with the use of glucose-oxidase methods of testing for glucosuria.
Other side effects that have been reported with levodopa are:
Nervous System: Ataxia, numbness, increased hand tremor, muscle twitching, blepharospasm, muscle cramps, trismus, activation of latent Horner's syndrome.
Psychiatric: Confusion, sleepiness, insomnia, nightmares, hallucinations, delusions, agitation, anxiety, euphoria.
Gastrointestinal: Dry mouth, bitter taste, sialorrhea, dysphagia, bruxism, hiccups, abdominal pain and distress, constipation, diarrhea, flatulence, burning sensation of tongue.
Metabolic: Weight gain or loss, edema.
Integumentary: Flushing, increased sweating, dark sweat, rash, hair loss.
Genitourinary: Urinary retention, urinary incontinence, dark urine, priapism.
Special Senses: Diplopia, blurred vision, dilated pupils and oculogyric crises.
Miscellaneous: Weakness, faintness, fatigue, headache, hoarseness, malaise, hot flashes, sense of stimulation, bizarre breathing patterns, neuroleptic malignant syndrome, malignant melanoma (see Contraindications).
