Api 4000 triple quadrupole mass spectrometer

Gamithromycin concentrations in serum were determined by a validated HPLC-MS/MS method using an Agilent 1200 HPLC system linked to an API 4000 triple quadrupole mass spectrometer as previously reported [8 (link), 31 (link)]. In brief, serum samples (0.5 mL) were mixed with 0.5 mL of acetonitrile, followed by vortex and centrifugation at 12,000×g for 10 min. The resulting supernatant was filtered through a 0.22 μm nylon syringe filter. Matrix matched calibration standards gave linear responses from 0.001 to 0.5 mg/L (R² > 0.996), with limits of quantification (LOQ) of 0.0005 mg/L. All samples with drug levels > 0.5 mg/L were diluted proportionally with control serum prior to extraction with acetonitrile. Recoveries of gamithromycin from serum ranged from 95.9 to 106.2%, and both the intraday and interday variations were < 9.27% (data not shown).
All PK parameters were measured using a non-compartmental model in WinNonlin software Version 5.2.1 (Pharsight, St. Louis, MO, USA). The absolute bioavailability (F) of gamithromycin in piglets was calculated from the following equation [21 (link), 32 (link)]:
$$\mathrm{F}\%=\frac{{\mathrm{AUC}}_{0-\infty \mathrm{IM}\text{or}\mathrm{SC}}}{{\mathrm{AUC}}_{0-\infty \mathrm{IV}}}\times 100\%$$