LC-MS/MS determination of Synercid injections.

Synercid is a combination of two semisynthetic pristinamycin derivatives, quinupristin and dalfopristin in 30:70 (w/w) ratio. A rapid and specific high-performance liquid chromatography-mass spectrometry was developed for the determination of quinupristin and dalfopristin using positive electrospray tandem mass spectrometry (+ESI-MS/MS). Multiple reaction monitoring transitions at 1023.05>134.34 and 691.87>166.26 were selected for the quantitation of quinupristin and dalfopristin, respectively. The assay run cycle-time was approximately 2.0 min injection-to-injection. The assay was linear up to concentration of 4000 ng x ml(-1) quinupristin and 1920 ng x ml(-1) dalfopristin. The lowest limits of quantitation of quinupristin and dalfopristin were found to be 1000 and 480 ng x ml(-1), respectively. Quantitation was based on peak area measurement of quinupristin and dalfopristin using weighed linear regression. Linear relationships with correlation coefficients (r>0.99) were automatically computed for both constituents by MASSLYNX quantify program. The ratio of the slopes of the calibration curves of quinupristin and dalfopristin was found to be 0.425, which matches the nominal ratio composition of the antimicrobial compounds in Synercid. The %RSD ranges were 2.3-4.0% for dalfopristin and 1.3-4.2% for quinupristin, whereas the %DEV ranges were (-7.5+3.7) and (-1.2+9.1%), respectively, indicating appropriate precision and accuracy. Recoveries of 99.5-103.8% and 97.8-99.0% of quinupristin and dalfopristin, respectively, were computed from Synercid injection. The described method is recommended for rapid determination of the contents and for tracking the stability and compatibility of quinupristin and dalfopristin in Synercid injection.