Carbidopa

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Cat Number

API28860959

CAS Number

28860-95-9

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CAS Number

28860-95-9

EINECS

249-271-9

Storage

Store at room temperature

Synonyms

Lodosyn; Carbidopa anhydrous; (S)-(-)-carbidopa; N-Aminomethyldopa; alpha-Methyldopahydrazine; Carbidopum; L-alpha-Methyldopahydrazine

Molecular Formula

C10H14N2O4

Molecular Weight

226.23

Smiles

C[C@](CC1=CC(=C(C=C1)O)O)(C(=O)O)NN

Appearance

White crystalline powder

Melting Point

203-205°C (dec.)

Boiling Point

367.84°C (rough estimate)

Relative Density

1.2616 (rough estimate)

General Description

Carbidopa is a peripheral decarboxylase inhibitor that does not cross the blood-brain barrier in significant amounts. Its chemical structure is a hydrazine derivative of DOPA, specifically (S)-α-(2-methyl-3-hydroxybenzyl)-hydrazine. Carbidopa is administered exclusively in combination with levodopa, as it has no antiparkinsonian activity of its own but prevents the peripheral metabolism of levodopa to dopamine.

Mechanism of Action

Carbidopa inhibits aromatic L-amino acid decarboxylase (AAAD), the enzyme responsible for converting levodopa to dopamine in peripheral tissues (gastrointestinal tract, liver, and kidney). By blocking this conversion, carbidopa increases the fraction of ingested levodopa that reaches the central nervous system unchanged, reducing the required levodopa dose by approximately 75%. The inhibition is irreversible, requiring new enzyme synthesis for recovery.

Application

Carbidopa is used exclusively as an adjunct to levodopa in the treatment of Parkinson's disease. The combination reduces peripheral side effects of levodopa (nausea, vomiting, hypotension) and eliminates the need for pyridoxine (vitamin B6) reversal. Carbidopa does not alter central metabolism of levodopa to dopamine. Fixed-ratio combinations (e.g., 1:4 or 1:10 carbidopa:levodopa) optimize peripheral inhibition while limiting central toxicity.

In a phase 3 RISE‑PD trial (630 patients with Parkinson disease and motor fluctuations), extended‑release IPX203 (carbidopa‑levodopa) dosed a mean 3 times daily was compared to immediate‑release carbidopa‑levodopa dosed 5 times daily over 13 weeks double‑blind. IPX203 significantly increased daily good on‑time (without troublesome dyskinesia) by 0.53 hours (95% CI 0.09‑0.97; P=0.02) and provided 1.55 more hours of good on‑time per dose. Adverse events were mild (nausea 4.3% vs. 0.8%). IPX203 offers a less frequent dosing regimen while improving motor response duration.

Fig. 1 Change From Baseline in Good On-Time, Least Squares Mean. (Hauser RA, et al., 2023)

References

Hauser RA, et al. IPX203 vs Immediate-Release Carbidopa-Levodopa for the Treatment of Motor Fluctuations in Parkinson Disease: The RISE-PD Randomized Clinical Trial. JAMA Neurol. 2023;80(10):1062-1069.

DUOGLOBE, a 36‑month prospective real‑world observational study of advanced Parkinson’s disease patients initiating levodopa‑carbidopa intestinal gel (LCIG), demonstrated sustained improvements in “Off” time (‑3.3 hours), dyskinesia, non‑motor symptoms, sleep, and daytime sleepiness (all p<0.05). Health‑related quality of life and caregiver burden improved through months 24 and 30. Safety was consistent with the known LCIG profile (54.9% serious adverse events; 27.2% discontinuations due to adverse events). LCIG provides long‑term real‑world benefits in motor and non‑motor symptoms.

Fig. 2 Stability of therapy over time. (Chaudhuri KR, et al., 2023)

References

Chaudhuri KR, et al. Levodopa Carbidopa Intestinal Gel in Advanced Parkinson's Disease: DUOGLOBE Final 3-Year Results. J Parkinsons Dis. 2023;13(5):769-783.

Does Carbidopa require protection from light and oxygen during storage?

Yes, it is highly sensitive to light and air. Oxidation and photodegradation cause discoloration (gray to brown). Store in airtight, light-resistant containers under inert gas if possible.

What is the recommended storage temperature for Carbidopa?

Store at controlled room temperature (15-25°C). Avoid excessive heat above 30°C, which accelerates oxidation and decarboxylation.

Is Carbidopa stable in combination tablet formulations with levodopa?

Yes, when formulated with antioxidants (e.g., ascorbic acid) and protected from light.

How is the impurity methyldopa (an oxidative degradation product) monitored?

This impurity is quantified using a stability-indicating HPLC method with electrochemical detection, ensuring it remains below pharmacopoeial limits.