Development and Validation of a Simultaneous HPLC Stability-Indicating Method for Atorvastatin and Apigenin in a Novel SMEDDS Formulation Using Quality by Design (QbD) Approach

Atorvastatin (ATV), a widely used statin, exhibits both cholesterol-lowering and anti-inflammatory effects. Apigenin (API), a natural flavonoid, also demonstrates potent anti-inflammatory activity. This study aimed to develop and validate a novel stability-indicating reverse-phase HPLC method for the simultaneous quantification of ATV and API in standard solutions and dual ATV–API-loaded self-microemulsifying drug delivery system (SMEDDS). Quality by Design (QbD) approach was used to define the quality target product profile (QTPP), critical quality attributes (CQAs), and identify critical method parameters (CMPs) through risk assessment. A central composite design (CCD) evaluated the effects of organic phase ratio, buffer pH, and flow rate on chromatographic responses, including retention time, tailing factor, and resolution. Separation was achieved using an Agilent Eclipse XDB C-18 column (5 µm, 4.6 × 150 min) with a mobile phase of acetonitrile and 0.1 M ammonium acetate buffer (pH 7.0) in a 40:60 (v/v) ratio, UV detection at 266 nm, and a flow rate of 0.4 mL/ min. The method met ICH and USP (2021) validation criteria, showing excellent linearity (0.1–10 µg/mL), precision, accuracy, and specificity. No interference from SMEDDS excipients or degradation products during stability studies was observed. This validated method offers a reliable tool for formulation development and routine analysis of ATV and API combinations