Liquid chromatographic determination of levodopa and levodopa-carbidopa in solid dosage forms: collaborative study

Area of Science:

• Analytical Chemistry
• Pharmaceutical Analysis

Background:

• Levodopa and carbidopa are crucial active pharmaceutical ingredients (APIs) for Parkinson's disease treatment.
• Accurate quantification of these APIs in pharmaceutical formulations is essential for patient safety and therapeutic efficacy.
• Existing analytical methods may require validation for diverse dosage forms.

Purpose of the Study:

• To collaboratively study and validate a liquid chromatographic method for determining levodopa and levodopa-carbidopa in pharmaceutical products.
• To assess the method's performance for both single-component levodopa and combination levodopa-carbidopa formulations.
• To evaluate the method's suitability for content uniformity testing of levodopa-carbidopa tablets.

Main Methods:

• A collaborative study involving 6 laboratories.
• Analysis of synthetic formulations, commercial tablets, and capsules containing levodopa and levodopa-carbidopa.
• Determination of repeatability (CVo) and reproducibility (CVx) coefficients of variation.
• Calculation of recovery values and pooled coefficients of variation (CVDo, CVDx) for tablet assays.

Main Results:

• Low coefficients of variation were observed for both repeatability and reproducibility across all tested formulations.
• Levodopa single component: CVo 0.48%, CVx 0.87%.
• Levodopa in combination: CVo 0.50%, CVx 0.90%.
• Carbidopa: CVo 0.77%, CVx 1.20%.
• High recovery rates for levodopa (100.4%) and carbidopa (99.5%) from synthetic formulations.
• Pooled CVDo/CVDx for individual tablet assays: Levodopa 2.07%/2.30%, Carbidopa 1.80%/2.24%.

Conclusions:

• The liquid chromatographic method is highly precise and accurate for quantifying levodopa and carbidopa in tablets and capsules.
• The method is suitable for routine quality control and content uniformity testing of these critical medications.
• The validated method has been adopted as official first action for the analysis of levodopa and levodopa-carbidopa formulations.