A Stability Indicating RP‐HPLC Method for Determination of Foslevodopa and Foscarbidopa in Bulk and Formulation

ABSTRACT The recently approved combination of foslevodopa and foscarbidopa by the United States Food and Drug Administration provides a major advancement in treatment of Parkinson's disease. This therapy helps to maintain consistent plasma levels of levodopa, thereby minimizing overall symptom in patients. A robust and validated RP‐HPLC method has been developed due to novelty of the drug combination and its recent approval by the regulatory agencies. The optimized chromatographic conditions included the use of a C18 column (250 × 4.6 mm, 5 µm), an isocratic mobile phase of acetonitrile: 0.1% formic acid (30:70), a flow rate of 1.0 mL/min, an injection volume of 10 µL, detection at 272 nm, and an ambient temperature of 25°C, with a total runtime of 6 min. Under these conditions, foslevodopa eluted at 2.087 min and foscarbidopa at 4.166 min. System suitability parameters, including plate count, tailing factor, and %RSD, were within acceptable limits. The method exhibited high precision, with %RSD values below 2%, and excellent linearity over a concentration range of 30–180 µg/mL for foslevodopa and 1.5–9 µg/mL for foscarbidopa. Sensitivity analysis determined LOD and LOQ values of 0.480 and 1.700 µg/mL for foslevodopa and 0.024 and 0.084 µg/mL for foscarbidopa, respectively. Degradation studies confirmed the stability indicating capability of the method under various stress conditions, with oxidative stress causing the highest degradation. The validated method was applied for assay of pharmaceutical formulation confirming compliance with label claims.