]> Kuturu D, Usalingam AK, et al. Volume 8 Issue 2 2581-4745 10.31531/2581-4745.1000174 Ribociclib RIBO and Letrozole LETRO are chemotherapeutic agents commonly used in combination therapy In this study a novel and robust bioanalytical LCMSMS method was developed for the simultaneous quantification of both drugs in human plasma The LCMSMS system was operated in positive ionization mode using the following source parameters collision gas 20 cone gas 20 desolvation gas 700 and source temperature 150C Chromatographic separation was achieved using Mobile Phase A consisting of a mixture of 01 formic acid pH adjusted to 35 with triethylamine and methanol 8020 vv and Mobile Phase B consisting of 5 acetonitrile The gradient program was initiated at 95 A and 5 B at 08 min shifted to 5 A and 95 B at 22 min and subsequently returned to 95 A and 5 B at 24 min which was maintained until 35 min An additional gradient step was incorporated to effectively eliminate carryover The developed method was fully validated within the relevant linearity ranges that encompassed the anticipated plasma concentrations of both analytes with correlation coefficients ranging from 09999 to 09939 Interday precision CV for RIBO ranged from 353 to 544 while LETRO showed values between 612 and 1312 Intraday precision ranged from 358 to 877 for RIBO and 249 to 1414 for LETRO These results comply with the EMA and ICH guidelines for bioanalytical method validation confirming the reliability and reproducibility of the method All Published Work is Licensed under a creative commons attribution 4.0 international license 2025