oa Development of RP-UPLC method for the assay and stability evaluation of letrozole in pharmaceutical emulgels

Purpose: The main objective of this study was to develop and validate a simple, rapid and stability-indicating ultra-performance liquid chromatography (UPLC) method for the determination of Letrozole in pharmaceutical gels. Methods: Chromatographic separation was achieved using Aquity UPLC BEH C-18 (2.1 x 50 mm, 1.7µm particle size) with an isocratic mobile phase consisting of acetonitrile: water (35:65, v/v). The flow rate was set to 0.3 ml/min, injection volume was set to 1µl, and the UV detection was carried out at λ= 240 nm. The method was validated as per ICH guidelines. Letrozole was subjected to different stress conditions (acidic, basic, oxidative, thermal, UV-radiation) to assess the stability indicating power of the developed UPLC method. Letrozole was also analyzed in different emulgel formulations containing a mixture of oil, surfactants, co-surfactants and gelling polymers. Furthermore, the stability of letrozole was assessed in the presence of different emulgel ingredients , where the mixtures of the saturated solubility studies were kept at 50°C, and then analyzed by the proposed method at predetermined time intervals. Results: The retention time of Letrozole was 1.80 min (RSD=0.12%). The method was linear over the concentration range of 2.5-200 µg/ml (R2 = 0.9999). The limit of detection (LOD) and the limit of quantitation (LOQ) were found to be 0.025 µg/ml and 0.125 µg/ml, respectively. The inter-day and intra-day precisions (% RSD) were less than 2%. All validation parameters were in the acceptable range. Neither the degradation products, nor the emulgel components interfere with the analysis of letrozole peak. Percentage recovery in emulgels were in agreement with the labeled spiked amounts. Letrozole was found unstable in the presence of PEG400, diethylene gycolmonoethyl ether, oleic acid, glycerylmonooleate when stored at high temperature of 50°C. Conclusions: The proposed method is simple, rapid, accurate, and can be successfully used for the analysis of letrozole's content and its stability in the pharmaceutical emulgels. Acknowledgements: This work has been financially supported by a grant to HM Younes and AA Sallam provided by Qatar National Research Foundation through the National Priorities Research Program grant # 4 - 496 - 3 - 157. Ahmed Abu Helwa is a research assistant financially supported by the same grant.