Green analytical chemistry and quality by design: A combined approach towards simultaneous determination of Letrozole with its co-administered Zoledronic Acid for cancer patients

Nowadays, breast cancer is the most affecting and globally diagnosed malignancy among women, yet Letrozole (LTZ) was considered the first-line treatment as hormonal anticancer drug. Unfortunately, LTZ develops osteoporosis as a main side effect which was overcome by using the co-administered; Zoledronic Acid (ZDA). Thus, there was a crucial need for this simultaneous quantification innovation, especially there were no any previously reported methods regarding both drugs together. In this study, an integrated framework was conducted between the experimental analytical quality-by-design (AQbD) approach and green analytical chemistry (GAC), emerging sensitive and robust RP-HPLC method. Box-Behnken Design was the developed model for optimizing an isocratic chromatographic separation on C₁₈ Equisil® ODS (4.6 × 250 mm, 5.0 μm) column at ambient temperature, using the mobile phase of 0.1 % aqueous trifluroacetic acid (pH 2.8): acetonitrile (54.5:45.5, v/v), at 1.0 mL/min flow rate with PDA detection at 254.0 nm and 210.0 nm for LTZ and ZDA, respectively. Model statistical and residual plots analysis was significant and normally distributed. Method was fully validated as per ICH guidelines, where good linearity was 0.20–10.00 µg/mL for both drugs in presence of Tadalafil (TDF) as an internal standard, obtaining adequate correlation coefficients (r) values. Calculated LOD results were 0.058 and 0.040 µg/mL while calculated LOQ results were 0.175 and 0.122 µg/mL for LTZ and ZDA, respectively. The proposed method was effectively applied on bulk, pharmaceutical dosage forms, and spiked human plasma. Statistical comparison of the anticipated results with the reported ones was performed. Greenness assessment was evaluated using Green Analytical Procedure Index (GAPI) and Analytical Greenness (AGREE) tools; where superiority results were achieved relative to other reported methods. Finally, an EVG method evaluation tool was assessed, and the attained results were represented through its radar chart.