DOPAR
Clinical safety rating: caution
Comprehensive clinical and safety monograph for DOPAR (DOPAR).
DOPAR (levodopa) is a metabolic precursor of dopamine. It crosses the blood-brain barrier and is converted to dopamine by aromatic L-amino acid decarboxylase (AADC) in the brain, thereby replenishing striatal dopamine levels and alleviating symptoms of Parkinson's disease.
| Metabolism | Primarily metabolized by aromatic L-amino acid decarboxylase (AADC) and catechol-O-methyltransferase (COMT) to dopamine, 3-O-methyldopa, and other metabolites. Also undergoes hepatic metabolism via monoamine oxidase (MAO). |
| Excretion | Renal: 70-80% as metabolites (including homovanillic acid, dihydroxyphenylacetic acid, and 3-O-methyldopa); biliary/fecal: ~20% as conjugates and metabolites; unchanged levodopa <1%. |
| Half-life | Terminal half-life: 1-3 hours (levodopa alone); with carbidopa (Sinemet): 1.5-2 hours due to reduced peripheral metabolism; clinical context: short half-life requires frequent dosing (every 4-6 hours) to maintain therapeutic levels. |
| Protein binding | ~10-15% bound to plasma proteins (mainly albumin); minimal binding due to small volume of distribution. |
| Volume of Distribution | Vd: 0.9-1.6 L/kg; clinical meaning: moderate distribution, primarily into extracellular fluid; limited CNS penetration due to peripheral metabolism; centrally, it is converted to dopamine. |
| Bioavailability | Oral: ~30-40% (levodopa alone, due to extensive first-pass metabolism); with carbidopa (Sinemet): ~90-99% due to inhibition of peripheral decarboxylase; enteral (duodenal) gel: ~70% (bypasses gastric emptying variability). |
| Onset of Action | Oral (immediate-release): 0.5-2 hours; peak effect at 1-2 hours. No parenteral or other routes clinically used. |
| Duration of Action | Duration: 3-6 hours for motor response; clinical notes: response duration may shorten with long-term therapy (wearing-off phenomenon); controlled-release formulations extend effect to 4-8 hours. |
| Action Class | Sympathomimetics agonist-Inotropes |
| Brand Substitutes | Dopacef 200mg Injection, Dopamine 200mg Injection, Dopmin 200mg Injection, Dopacard 200mg Injection, Dopamed 200mg Injection |
Levodopa 300-600 mg orally 3-4 times daily as Dopar; do not crush or chew extended-release.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for mild-moderate renal impairment; avoid in severe impairment (CrCl <30 mL/min) due to possible neurotoxicity. |
| Liver impairment | Child-Pugh A: no adjustment; Child-Pugh B: reduce dose by 25-50%; Child-Pugh C: contraindicated. |
| Pediatric use | Not recommended for use in children (safety and efficacy not established). |
| Geriatric use | Start at lower doses (e.g., 100 mg 2-3 times daily) with slow titration to minimize side effects such as orthostatic hypotension and neuropsychiatric effects; monitor for drug interactions. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for DOPAR (DOPAR).
| Breastfeeding | Levodopa is excreted into breast milk in small amounts. The M/P ratio is approximately 0.5-0.7. Limited data suggest infant exposure is low, but potential adverse effects on the nursing infant include irritability and changes in dopamine-mediated functions. Caution is advised; consider alternative therapies or monitor infant for effects. |
| Teratogenic Risk | DOPAR (levodopa) is classified as FDA Pregnancy Category C. Animal studies have shown adverse effects on fetal development, including skeletal abnormalities at doses higher than human therapeutic levels. In the first trimester, there is a potential risk of congenital malformations, though human data are limited. During the second and third trimesters, there may be increased risk of fetal distress and preterm labor. Levodopa crosses the placenta and may affect fetal dopamine metabolism. Use only if potential benefit justifies risk. |
■ FDA Black Box Warning
None
| Serious Effects |
Narrow-angle glaucoma, history of malignant melanoma, concomitant use with non-selective MAO inhibitors (within 14 days), and hypersensitivity to levodopa or any component.
| Precautions | May cause dyskinesias, psychiatric disturbances (hallucinations, psychosis), neuroleptic malignant syndrome-like symptoms upon abrupt withdrawal, and melanoma risk. Caution in patients with severe cardiovascular or pulmonary disease, bronchial asthma, renal, hepatic, or endocrine disease. May induce orthostatic hypotension. |
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| Fetal Monitoring | Monitor maternal blood pressure, heart rate, and signs of dyskinesia or psychiatric changes. Assess fetal growth and well-being via ultrasound for growth restriction and consider fetal heart rate monitoring in cases of maternal hypertension or preeclampsia. Monitor for preterm labor. Evaluate for gestational diabetes as levodopa may affect glucose metabolism. |
| Fertility Effects | Levodopa may affect fertility by altering prolactin levels and gonadal function. It can inhibit prolactin secretion, potentially affecting ovulation and menstrual regularity. Reversible decreases in sperm count and motility have been reported in males. Overall, impact on fertility is generally minimal but should be considered in patients attempting conception. |