Background:
Accurate and validated bioanalytical methods are essential for drug quantification in biological matrices to support pharmacokinetic and therapeutic drug monitoring studies. Palbociclib, Ribociclib and Letrozole are clinically relevant drugs; however, to date, no simultaneous bioanalytical method has been reported for their estimation in human plasma using HPLC-UV.

Materials and Methods:
A simple and sensitive high-performance liquid chromatography with ultraviolet detection (HPLC-UV) method was developed and validated for simultaneous determination of Palbociclib, Ribociclib and Letrozole in spiked human plasma. Sample preparation was performed using protein precipitation with acetonitrile. Separation was achieved on an Orochemorosil C18 column (250 × 4.6 mm, 5 µm) using a mobile phase of phosphate buffer (pH 3.0, 10 mM) and acetonitrile (60:40, v/v) at a flow rate of 1.0 mL/min. Detection was carried out at 260 nm.

Results:
The method was linear over the ranges of 10–300 ng/mL (Palbociclib), 10–1000 ng/mL (Ribociclib ), and 10–600 ng/mL (Letrozole ) with correlation coefficients meeting ICH M10 acceptance criteria. Accuracy, precision, recovery, and selectivity were within acceptable limits. Stability studies in plasma and stock solutions confirmed analyte stability under all tested conditions, with negligible degradation observed. The optimized method demonstrated a short chromatographic runtime and simple sample preparation, enabling rapid analysis of multiple samples.

Conclusion:
The validated HPLC-UV method is simple, precise, and robust. It offers the first reported simultaneous quantification of Palbociclib, Ribociclib and Letrozole in human plasma and is suitable for pharmacokinetic studies, bioequivalence testing, and therapeutic drug monitoring in clinical trails