Overestimation of vancomycin concentrations utilizing fluorescence polarization immunoassay in patients on peritoneal dialysis.

During a study of vancomycin pharmacokinetics in patients undergoing continuous ambulatory peritoneal dialysis (CAPD), a discrepancy was noted when serum concentrations were determined by high performance liquid chromatography (HPLC) in comparison to a fluorescence polarization immunoassay (FPI) technique. Following three weekly intraperitoneal doses (30 mg/kg/2 L), peak serum concentrations (at the end of the 6-h dwell) by FPI were 42.1 +/- 9.1, 43.1 +/- 8.7, and 45.6 +/- 7.4 micrograms/ml. In comparison, the same samples when analyzed by HPLC yielded 36.3 +/- 9.4, 32.2 +/- 8.9, and 31.6 +/- 9.1 micrograms/ml, respectively. A subsequent in vitro study of vancomycin (40 micrograms/ml) in serum indicated a degradation half-life of 693 (FPI) compared with 210 (HPLC) h. These data suggest that vancomycin degradation products accumulate in CAPD patients and lead to an overestimation of vancomycin serum concentrations when measured by FPI.