A validated, stability-indicating HPLC method for the determination of dexamethasone related substances on dexamethasone-coated drug-eluting stents

An HPLC method was developed and validated to determine trace amounts of dexamethasone related substances on dexamethasone-coated drug-eluting stents. Separation of dexamethasone from its major process impurities and degradation products was achieved on a Zorbax Eclipse XDB C8 column using gradient elution and UV detection at 239 nm. The method was validated according to ICH guideline requirements. In addition, stent extraction efficiency, solution stability and method robustness were evaluated. The method was determined to be linear in the range of 0.01-0.30 microg ml(-1) for the quantitation of major dexamethasone related substances. Method accuracy was assessed by spiking dexamethasone acetate at three levels over the range of 0.025-0.175 microg ml(-1). The dexamethasone acetate recovery ranged from 89.6 to 105.8%. The intermediate precision over the three levels was less than 6% (n=9). The method was also shown to be repeatable at concentration levels of 0.025, 0.125 and 0.175 microg ml(-1) dexamethasone with relative standard deviation values of 4.1, 1.7 and 1.6%, respectively. The method was found to be specific, stability-indicating, and sensitive with a detection limit of 0.008 microg ml(-1) and a quantitation limit of 0.025 microg ml(-1) dexamethasone. Finally, the method was demonstrated to be robust, resistant to small variations of chromatographic variables such as pH, mobile phase organic/aqueous composition and column temperature. Identifying unknown dexamethasone degradation products in dexamethasone-coated drug-eluting stents was of critical interest to ensure product quality, since degradants have a significant impact on safety, efficacy, and product storage and handling. The developed chromatographic method was designed to be compatible with mass spectrometric detection. This paper also discusses using this chromatographic method coupled to an ion-trap LCQ mass spectrometer to elucidate proposed structures for four major dexamethasone degradants.