From Separation to Safety Prediction: Validated RP-HPLC Method for Simultaneous Estimation of Sitagliptin and...

Diabetes mellitus is a global health burden, necessitating effective combination therapies. The fixed-dose formulation of sitagliptin phosphate (SGP, 100 mg) and lobeglitazone sulfate (LGS, 0.5 mg) offers synergistic benefits by enhancing insulin sensitivity and glucose-dependent insulin secretion. However, simultaneous quantification remains challenging due to their dosage disparity and the narrow therapeutic index of LGS. This study reports a validated, stability-indicating RP-HPLC method for concurrent estimation of SGP and LGS in a synthetic mixture. Separation was achieved on a Pursuit 5 Diphenyl column (150 × 4.6 mm, 5 μm) using a gradient of 0.1% formic acid and acetonitrile at 1.0 mL/min, with PDA detection at 254 nm. The method complied with ICH Q2(R2) guidelines, showing specificity, linearity, accuracy, precision, and robustness. Forced degradation studies revealed marked instability of SGP under acidic and alkaline conditions, whereas LGS remained stable. LC-MS/MS analysis identified a major degradation product at m/z 234, and probable fragmentation pathways were proposed. In silico ADMET and toxicity profiling predicted high gastrointestinal absorption for all degradation products, with PI-1 and PI-2 flagged for carcinogenicity and all except PI-3 showing nephrotoxicity. This integrated analytical-computational approach provides a reliable tool for quality control and safety assessment of this antidiabetic formulation.