Determination of roxythromycin in blood serum by liquid chromatography with mass spectrometric detection

A procedure has been developed for the determination of a macrolide antibiotic roxythromycin (RX) in blood serum using HPLC with mass spectrometric detection using clarithromycin (CL) as the internal standard. RX and CL have been extracted from the samples by solid-phase extraction in a cartridge filled with a polar adsorbent, cyanopropylsilyl silica gel. The absolute recoveries of RX and CL are 89.6 and 92.5%, respectively. Chromatographic separation has been performed on a Nucleodur C₁₈ Isis column with the mobile phase composed as follows: water-methanol-acetonitrile-formic aid (499: 250: 250: 1 by volume). Registration has been performed in the mode of selected ion monitoring with m/z 837.7 (RX) and m/z 748.7 (CL). The analytical range for RX is 0.097–14.81 μg/mL, the quantification limit is 0.097 μg/mL, the detection limit is 0.03 μg/mL, and the intraday and interday relative standard deviation are 2–6 and 4–8% respectively. The procedure has been applied to the pharmacokinetic studies of the Rulid pharmaceutical preparation.