Levodopa/Carbidopa (Sinemet)
Dopaminergic cornerstone of Parkinson's disease treatment. Levodopa (L-DOPA) is the metabolic precursor to dopamine and crosses the blood-brain barrier via LAT1, where it is decarboxylated to dopamine by aromatic L-amino acid decarboxylase (AADC). Carbidopa is a peripheral AADC inhibitor that does not cross the BBB; it prevents premature peripheral decarboxylation, dramatically increasing CNS levodopa delivery (~10x) and reducing peripheral dopaminergic side effects (nausea, orthostasis). Pyridoxine (vitamin B6) reverses peripheral decarboxylase inhibition unless carbidopa is co-administered, as B6 is an AADC cofactor. High-protein meals compete for LAT1 transport at gut and BBB. Long-term therapy produces motor fluctuations (wearing-off, on-off phenomenon) and dyskinesias. Dose typically expressed as levodopa mg component in fixed 4:1 or 10:1 ratio with carbidopa.
Projected serum levels — 100 mg, once daily
Maintenance schedule: 100 mg once daily (oral).
Modeled steady state after ~1 days: peak ≈ 47.8 mg, trough ≈ 0.33 mg body load. Population-based estimate over 15 days for a 100 mg dose at a 70 kg reference body mass — the interactive app scales curves to your doses, timing, and body mass.
Key facts
- Category
- Antiparkinsonian
- Route modeled
- Oral
- Model confidence
- inferred
- Half-life
- 3 h
- Common dose
- 100 mg
- Suggested maximum
- 800 mg/day
- Reference dose range
- 50–800 mg (single dose)
- Suggested cadence
- once daily
Documented interactions
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moderate
Green Tea Extract (Camellia sinensis) + Levodopa/Carbidopa (Sinemet)
Green Tea Extract (Camellia sinensis) reversible_inhibitor of COMT predicted to change Levodopa/Carbidopa (Sinemet) AUC by ~1.37x
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moderate
LSA (Ergine / Lysergic Acid Amide) + Levodopa/Carbidopa (Sinemet)
Levodopa/Carbidopa (Sinemet) and LSA (Ergine / Lysergic Acid Amide) both push the dopamine D1 and dopamine D2 in the same direction.
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watch
1P-LSD (1-Propionyl-LSD) + Levodopa/Carbidopa (Sinemet)
1P-LSD (1-Propionyl-LSD) and Levodopa/Carbidopa (Sinemet) both push the dopamine D2 in the same direction.
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watch
Aripiprazole (Abilify) + Levodopa/Carbidopa (Sinemet)
Aripiprazole (Abilify) and Levodopa/Carbidopa (Sinemet) both push the dopamine D2 in the same direction.
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watch
Brexpiprazole (Rexulti) + Levodopa/Carbidopa (Sinemet)
Brexpiprazole (Rexulti) and Levodopa/Carbidopa (Sinemet) both push the dopamine D2 in the same direction.
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watch
Cariprazine (Vraylar) + Levodopa/Carbidopa (Sinemet)
Cariprazine (Vraylar) and Levodopa/Carbidopa (Sinemet) both push the dopamine D2 in the same direction.
Serum checks 13 modeled interaction pairings for levodopa/carbidopa (sinemet) across your whole stack — absorption conflicts, enzyme inhibition, and nutrient depletion included.
Research behind this entry
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Levodopa and the progression of Parkinson's disease (ELLDOPA)
Landmark ELLDOPA trial of 361 early PD patients randomized to placebo or levodopa 150-600 mg/day for 40 weeks. Levodopa produced dose-dependent improvement in UPDRS scores, but the 600 mg group showed more dyskinesia…
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Effect of deprenyl on the progression of disability in early Parkinson's disease (DATATOP)
DATATOP trial of 800 patients demonstrating selegiline 10 mg/day delayed the need for levodopa therapy by ~9 months, establishing MAO-B inhibition as an early-PD disease-modifying strategy and levodopa-sparing approach.
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Pharmacokinetics of levodopa
Foundational PK review establishing levodopa's short half-life (~1.5 h with carbidopa), the role of dietary amino acid competition at LAT1, and the pharmacokinetic basis for motor fluctuations (wearing-off) as a…
3 published studies referenced in the app, each with a plain-language summary.