Stability-indicating LC-analytical method development and validation for the simultaneous estimation of flucloxacillin and amoxicillin in pharmaceutical dosage form

A simple and rapid stability-indicating LC-analytical method was developed for the simultaneous determination of flucloxacillin (fluc) and amoxicillin (amox) in bulk and pharmaceutical dosage form. A chromatographic separation of the two drugs was achieved with a Thermosil C18 (4.6 mm × 250 mm, 5 μm) analytical column using potassium dihydrogen phosphate buffer (adjusted to pH 3 by ortho phosphoric acid):methanol (70:30%, v/v) in isocratic mode at a flow rate of 1 mL/min and column at ambient temperature. The detection was monitored at 225 nm using a PDA detector. The stressed samples were analyzed for the degradation study in acid, base, peroxide, thermal, photolytic and validated as per ICH guideline. This proposed method was found to be specific and stability-indicating as no interfering peaks of degradation compounds and excipients were noticed. The described method shows excellent linearity over a range of 20–100 μg/mL for both drugs. The correlation coefficient for fluc and amox was 0.9992 and 0.9993, respectively. The mean recovery value for fluc and amox was 99.9% and 99.7%, respectively. The limit of detection for fluc and amox was 0.018 and 0.009 μg/mL and the limit of quantification was 0.06 and 0.03 μg/mL, respectively. The retention time was observed at 2.582 and 3.407 min for amox and fluc, respectively. The robustness study and percentage of assay of the formulation were found within limit as per ICH guidelines. The proposed method was suitable for quantitative determination and it can be applied in quality control department in industries, approved testing laboratories, bio-pharmaceutics and bio-equivalence and clinical pharmacokinetic studies.