In vitro evaluation of a vancomycin radioimmunoassay and observations on vancomycin pharmacokinetics in dialysis patients

A recently marketed radioimmunoassay (RIA) for vancomycin (Monitor Science Corp.) was evaluated in vitro and in vivo. The RIA and bioassay results on 15 spiked serum samples found no significant difference between the two assays, although RIA results were significantly less variable. The coefficient of variation (RIA) was 5.5%. Vancomycin showed no significant degradation in plasma at 4 degrees C and -20 degrees C for up to 36 days. Five dialysis patients had a total of 62 serum levels determined. When vancomycin 1 g was given weekly to two anuric adults, marked accumulation occurred. This finding was consistent with vancomycin's long terminal half-life (19.8 and 17.8 days) obtained from a new computer subroutine which obtains least square estimators of model parameters from multiple dose data. Despite serum levels well above the MIC, two patients remained bacteremic. Peritoneal levels of vancomycin in two patients with suspected peritonitis equalled corresponding serum levels.