Stability-indicating methods for the determination of linezolid in the presence of its alkaline-induced degradation products.

Three methods are presented for the determination of linezolid in the presence of its alkaline-induced degradation products. The first method was based on separation of linezolid from its alkaline degradation product by TLC followed by densitometric measurement of the spots of intact drug at 244 nm. The separation was carried out on silica gel 60 F(254) using isobutanol:ammonia (9:1 v/v) as a mobile phase. The second method was based on first derivative (1)D ultraviolet spectrophotometry with zero crossing point and peak to base measurement. The (1)D value at 251.4 nm was selected for the assay of linezolid in the presence of degradation product. The third method was depended on the first derivative of the ratio spectra (1)DD by measurement of the value at 263.6 nm. The proposed methods were successfully applied to the determination of the drug in bulk powder, in laboratory prepared mixtures with its degradation product and in commercial tablets.