"RP-HPLC METHOD DEVELOPMENT AND VALIDATION FOR SIMULTANEOUS ESTIMATION OF LINEZOLID AND DAPTOMYCIN AND THEIR IMPURITIES."

ABSTRACT
The present study was aimed at the development and validation of a simple, accurate, precise,
and stability-indicating gradient RP-HPLC method for the simultaneous estimation and
impurity profiling of Linezolid and Daptomycin in pharmaceutical formulations. Both
antibacterial agents are therapeutically important in the treatment of resistant Gram-positive
bacterial infections such as Methicillin-Resistant Staphylococcus aureus (MRSA) and
Vancomycin-Resistant Enterococci (VRE). Due to significant differences in molecular weight,
polarity, and chromatographic behavior between Linezolid and Daptomycin, simultaneous

estimation using conventional analytical methods is challenging. Therefore, a gradient RP-
HPLC method was developed using a C18 column (250 mm × 4.6 mm, 5 μm) with phosphate

buffer (pH 4.0) and acetonitrile as the mobile phase in gradient mode. Detection was carried
out at 230 nm with a flow rate of 1.0 mL/min and total run time of 20 minutes.
The developed method provided satisfactory separation with retention times of 4.28 minutes
for Linezolid and 10.62 minutes for Daptomycin. The method was validated according to ICH
Q2(R1) guidelines for parameters including specificity, linearity, accuracy, precision,
robustness, ruggedness, limit of detection, and limit of quantitation. The calibration curves for
both drugs showed excellent linearity over the concentration range of 10–100 μg/mL with
correlation coefficients greater than 0.999. Recovery studies demonstrated high accuracy with
percentage recovery within acceptable limits of 98–102%. Precision studies showed low
%RSD values below 2%, indicating excellent reproducibility of the analytical method.
Forced degradation studies under acidic, alkaline, oxidative, thermal, and photolytic conditions
confirmed the stability-indicating capability of the method. Degradation products were

effectively separated from the parent drug peaks without interference. The developed RP-
HPLC method was successfully applied for assay of marketed formulations and was found

suitable for routine pharmaceutical quality control, stability studies, and impurity profiling of
Linezolid and Daptomycin.