Determination of total cefozopran concentrations in human peritoneal fluid by HPLC with cefepime as an internal standard: Comparative pharmacokinetics in the fluid and plasma

A simple, rapid and precise HPLC method using ultrafiltration to remove protein was developed to determine total cefozopran concentrations in human peritoneal fluid in the same manner as in human plasma, irrespective of the amount of protein. The recovery of cefozopran after ultrafiltration in peritoneal fluid was higher than that in plasma, because the protein content in peritoneal fluid was lower than that in plasma. Furthermore, it was found that an internal standard with a similar protein-binding ratio to cefozopran could revise the cefozopran loss by ultrafiltration in plasma and peritoneal fluid samples irrespective of the amount of protein. Therefore, it was concluded that cefepime may be used as an internal standard. Cefozopran and cefepime were detected by measuring their ultraviolet absorbances at 235 nm. The calibration curve obtained for cefozopran in peritoneal fluid was linear from 0.2 to 200 μg/ml. The intraday and interday precisions were less than 5.77% (CV), and the accuracy was between 96.3% and 108% above 0.2 μg/ml. The lower limit of detection was 0.05 μg/ml in peritoneal fluid, which was the same as that in plasma. The assay has been applied to therapeutic drug monitoring of cefozopran in both plasma and peritoneal fluid and has contributed to peritoneal pharmacokinetic studies in patients.