Quantification of cefazolin in serum and adipose tissue by ultra high performance liquid chromatography-Tandem mass spectrometry (UHPLC–MS/MS): application to a pilot study of obese women undergoing cesarean delivery

• The first UHPLC–MS/MS assay using a stable-isotope cefazolin internal standard.
• Cefazolin is extracted from adipose tissue using a hexane/buffer solvent extraction.
• Cefazolin concentrations in adipose tissue are half the minimum inhibitory concentration.
• The concentration of cefazolin was more than 26-fold higher in serum than adipose.

Higher doses of cefazolin are required in obese patients for preoperative antibiotic prophylaxis, owing to its low lipophilicity. An ultra high performance liquid chromatography-tandem mass spectrometry method was developed to quantify cefazolin in serum and adipose tissue from 6 obese patients undergoing cesarean delivery, and using stable-isotope labeled cefazolin as an internal standard. The method has a 2 μg/g lower limit of quantitation. The concentration in adipose tissue was 3.4 ± 1.6 μg/mL, which is less than half of the reported minimum inhibitory concentration of 8 μg/mL for cefazolin. Serum cefazolin concentrations were more than 30-fold higher than in adipose tissue.