A stability indicating UPLC method development and validation for the simultaneous estimation of nateglinide and metformin hydrochloride in bulk and tablet dosage form

Background Nateglinide and metformin HCl are used in combination for the treatment of type 2 diabetes. A simple, sensitive and reliable UPLC method was developed for simultaneous estimation of nateglinide and metformin HCl using Phenomenox C 18 (50*2.1 mm, 3.5 µm) column at ambient temperature as stationary phase in addition to mobile phase containing 75 volumes of ammonium formate buffer (pH = 3) along with 25 volumes of acetonitrile with a flow rate of 0.2 mL/min with UV detection at 260 nm and a run time of 3 min. The developed method was validated as per ICH Q2(R1) guidelines. Results The separation of metformin HCl and nateglinide was done at retention times of 1.014 min and 1.435 min, respectively. The mean % recovery for nateglinide and metformin HCl in the accuracy study was observed to be 99.9% and 99.2%, respectively. LOD and LOQ values were determined considering the S/N ratio and were found to be 0.09 µg/mL and 0.3 µg/mL, respectively, for nateglinide and 0.75 µg/mL and 2.5 µg/mL, respectively, for metformin HCl. The method was found to be precise with % RSD values of 0.58 and 0.45, respectively, for repeatability and intermediate precision of nateglinide and 0.43 and 0.43, respectively, for repeatability and intermediate precision of metformin HCl which were within acceptance criteria. The method was found to be linear in the range of 7.5–45 µg/mL and 62.5–375 μg/mL for nateglinide and metformin HCl, respectively. The regression equations for nateglinide and metformin HCl were found to be y = 17377 x + 6543.4 and y = 18439 x + 43,537, respectively. The method was found to be robust by deliberate changes in the method parameters like flow rate and mobile phase composition. Forced degradation studies were performed as per ICH Q1A(R2) and Q1B guidelines, and peak purity was observed in all types of degradation studies for both the drugs. Conclusion The developed method was found to be satisfactory as it is simple, sensitive, accurate, precise, robust, rapid, economical and yet stability indicating and can be applied successfully in the routine laboratory analysis for the simultaneous estimation of nateglinide and metformin HCl in the bulk and pharmaceutical dosage forms.