Common Side Effects of Sinemet (Carbidopa/Levodopa)
The most common side effects of Sinemet (carbidopa/levodopa) include dyskinesias (involuntary movements) and nausea, as reported in the FDA drug label. 1
Gastrointestinal Side Effects
- Nausea (very common)
- Vomiting
- Dark saliva
- Gastrointestinal bleeding
- Anorexia
- Diarrhea
- Constipation
- Dyspepsia (indigestion)
- Dry mouth
- Taste alterations
- Abdominal pain
- Dysphagia (difficulty swallowing)
- Sialorrhea (excessive salivation)
- Flatulence
- Bruxism (teeth grinding)
Neurological and Psychiatric Side Effects
- Dyskinesias (choreiform, dystonic, and other involuntary movements)
- "On-off" phenomenon (bradykinetic episodes)
- Confusion
- Dizziness
- Somnolence (drowsiness)
- Headache
- Insomnia
- Nightmares and abnormal dreams
- Paresthesia (tingling sensations)
- Depression (sometimes with suicidal tendencies)
- Psychotic episodes including:
- Delusions
- Hallucinations
- Paranoid ideation
- Agitation
- Dementia
- Impulse control disorders:
- Pathological gambling
- Increased libido/hypersexuality
Cardiovascular Side Effects
- Orthostatic hypotension
- Cardiac irregularities
- Hypertension
- Syncope (fainting)
- Palpitations
- Phlebitis
Other Notable Side Effects
- Increased sweating
- Dark urine
- Rash
- Fatigue/asthenia (weakness)
- Muscle cramps
- Back/shoulder pain
- Dyspnea (shortness of breath)
- Upper respiratory infections
Laboratory Abnormalities
- Decreased hemoglobin and hematocrit
- Abnormalities in liver enzymes (alkaline phosphatase, AST, ALT, LDH)
- Elevated bilirubin and BUN
- Positive Coombs test
- Elevated serum glucose
- White blood cells, bacteria, and blood in urine
Rare but Serious Side Effects
- Agranulocytosis
- Hemolytic and non-hemolytic anemia
- Thrombocytopenia
- Leukopenia
- Angioedema
- Urticaria
- Henoch-Schönlein purpura
- Bullous lesions (including pemphigus-like reactions)
Clinical Considerations
- Side effects often appear more prominently in the first 3 years of treatment 2
- The controlled-release formulation (Sinemet CR) may be associated with fewer motor fluctuations and dyskinesias compared to immediate-release formulations 3, 4
- Patients on controlled-release formulations may experience more sustained "on" time (83% vs 62%) compared to standard formulations 4
- Dosage adjustments may be necessary to balance symptom control with side effects
Monitoring Recommendations
- Regular assessment of motor symptoms and side effects
- Monitoring for development of impulse control disorders
- Observation for signs of psychosis, especially in elderly patients
- Periodic laboratory tests to monitor blood counts and liver function
Understanding these common side effects is essential for proper management of patients on carbidopa/levodopa therapy, as they significantly impact quality of life and treatment adherence.