SINEMET CR
Clinical safety rating: caution
Comprehensive clinical and safety monograph for SINEMET CR (SINEMET CR).
Sinemet CR is a combination of carbidopa and levodopa. Levodopa is converted to dopamine in the brain via aromatic L-amino acid decarboxylase (AAAD), thereby restoring dopamine levels in the striatum. Carbidopa inhibits peripheral decarboxylation of levodopa, increasing levodopa availability to the brain and reducing peripheral side effects.
| Metabolism | Levodopa is extensively metabolized peripherally by aromatic L-amino acid decarboxylase (AAAD) and catechol-O-methyltransferase (COMT); carbidopa is metabolized by AAAD and is not extensively metabolized otherwise. |
| Excretion | Renal: 70-80% as metabolites (mainly HVA and DOPAC) and unchanged drug (less than 10% for levodopa, 30% for carbidopa); fecal: 5-10%; biliary: 5%. |
| Half-life | Levodopa: 1.5-2.5 hours (terminal half-life prolonged in older patients or with carbidopa); carbidopa: 1-2 hours. The controlled-release formulation extends the apparent half-life to 4-6 hours due to continued absorption. |
| Protein binding | Levodopa: about 10-30% (mostly albumin); carbidopa: about 36% (albumin). |
| Volume of Distribution | Levodopa: 0.9-1.3 L/kg (widely distributed, but does not cross the blood-brain barrier efficiently without carbidopa; Vd indicates extensive tissue uptake); carbidopa: 0.5-0.8 L/kg. |
| Bioavailability | Oral: 70-75% relative to levodopa alone when combined with carbidopa (due to decarboxylase inhibition); absolute bioavailability: about 40-50% for levodopa component due to first-pass metabolism. |
| Onset of Action | Oral: 30-60 minutes (compared to 20-30 minutes for immediate-release), with more gradual peak effect. |
| Duration of Action | Oral: 6-8 hours (clinical benefit may last up to 8 hours, but response may decrease with chronic use; often requires dosing 3-4 times daily). |
Oral, 1 tablet (carbidopa 50 mg / levodopa 200 mg) twice daily at intervals of at least 6 hours; maximum 6 tablets per day.
| Dosage form | TABLET, EXTENDED RELEASE |
| Renal impairment | GFR 15-50 mL/min: No adjustment needed; GFR <15 mL/min: Use with caution, consider dose reduction based on response and tolerability; hemodialysis: Not studied, avoid if possible. |
| Liver impairment | Child-Pugh A: No adjustment; Child-Pugh B: Start at lower end of dosing range, monitor closely; Child-Pugh C: Avoid use due to lack of data. |
| Pediatric use | Not recommended for use in pediatric patients (<18 years) due to lack of safety and efficacy data. |
| Geriatric use | Initiate with low doses (e.g., carbidopa 25 mg/levodopa 100 mg once daily); titrate slowly due to increased risk of orthostatic hypotension and hallucinations; monitor renal function. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for SINEMET CR (SINEMET CR).
| Breastfeeding | Levodopa is excreted into breast milk in low concentrations; the M/P ratio is approximately 1.0. Carbidopa is also excreted but at lower levels. Potential for infant dopamine receptor blockade. Breastfeeding not recommended due to unknown effects on developing nervous system; if used, monitor infant for extrapyramidal symptoms. |
| Teratogenic Risk | Insufficient human data. In animal studies, carbidopa-levodopa caused visceral and skeletal malformations at doses below human therapeutic exposure (rats, rabbits). First trimester: avoid unless benefit outweighs risk. Second/third trimesters: limited data, no definitive association with major malformations; theoretical risk of fetal catecholamine depletion. |
■ FDA Black Box Warning
None
| Serious Effects |
["Concurrent use with nonselective monoamine oxidase inhibitors (MAOIs) or within 2 weeks of discontinuing MAOIs","Known hypersensitivity to any component of the formulation","Narrow-angle glaucoma","Suspicious, undiagnosed skin lesions or history of melanoma"]
| Precautions | ["May cause somnolence and sudden sleep onset; advise caution with driving or operating machinery.","May cause dyskinesias or exacerbate existing dyskinesias.","May cause hallucinations, psychotic-like behavior, or confusion.","May cause impulse control disorders (e.g., compulsive gambling, hypersexuality).","May cause orthostatic hypotension; monitor blood pressure.","May cause neuroleptic malignant syndrome (NMS) upon abrupt withdrawal; taper gradually.","Use caution in patients with severe cardiovascular, pulmonary, renal, hepatic, or endocrine disease.","May cause melanoma; monitor skin lesions."] |
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| Fetal Monitoring | Monitor maternal blood pressure, heart rate, and signs of dyskinesia or psychiatric symptoms. Fetal growth assessment via ultrasound (growth restriction in animal studies). Consider fetal heart rate monitoring in late pregnancy due to risk of maternal hypotension. Postnatal: monitor neonate for extrapyramidal side effects. |
| Fertility Effects | Limited data; carbidopa-levodopa may impair fertility in animal studies (decreased implantation, increased preimplantation loss). No human studies on fertility. Dopaminergic effects may alter prolactin and gonadotropin secretion, potentially affecting ovulation and spermatogenesis. |