Green, innovative oral capsules of three anti-Parkinson’s drugs: formulation, <i>in vitro</i> evaluation, and robust RP-HPLC validation

Parkinson's disease (PD) remains a debilitating neurodegenerative disorder, with levodopa (LEV) as the cornerstone of its management. However, the long-term use of LEV is often complicated by motor fluctuations and dyskinesias, necessitating adjunct therapies such as carbidopa (CAR) and safinamide (SAF) to enhance efficacy and reduce side effects. Despite the promising therapeutic potential of this combination, the simultaneous analysis of the three drugs in pharmaceutical formulations poses significant analytical challenges. This study addresses this critical gap by developing and validating a sensitive and specific reversed-phase high-performance liquid chromatography (RP-HPLC) method for their simultaneous quantification in pure forms and in-house oral capsule formulations. The optimized method utilized a gradient elution using phosphate buffer (pH 3, 0.1 M) and acetonitrile as the mobile phase, a C8 stationary phase, and UV detection at 240 nm, achieving baseline separation within 11 min. Validation studies demonstrated excellent linearity, precision (RSD < 2%), accuracy (recovery 98.97-100%), and robustness, with LODs of 0.063 μg mL^-1, 0.112 μg mL^-1, and 0.058 μg mL^-1, and LOQs of 0.190 μg mL^-1, 0.341 μg mL^-1, and 0.177 μg mL^-1 for LEV, CAR, and SAF, respectively. The in-house capsule formulation exhibited uniform drug content (90-110% of label claim), rapid disintegration (<8 min), and complete dissolution of LEV and CAR within 45 min, while SAF showed sustained release over 60 min. The method is offering a reliable and sustainable approach for quality control, pharmaceutical analysis, and industrial applications. The greenness profile of the method was rigorously evaluated using the NEMI, AGP, ESA, AGREE, and MoGAPI methods. Furthermore, the blueness of the technique was studied using the BAGI method, confirming its alignment with green analytical chemistry principles.