TROUGH SERUM VANCOMYCIN LEVELS PREDICT THE RELAPSE OF GRAM-POSITIVE PERITONITIS IN PERITONEAL-DIALYSIS PATIENTS

We reviewed 31 episodes of gram-positive peritonitis that occurred in our peritoneal dialysis population between 1990 and 1993 in an attempt to identify the risk factor(s) for peritonitis relapse. All patients were treated with 4 weekly doses of intravenous vancomycin. Vancomycin doses no. 1 and 2 were based on body weight (15 mg/kg with a 1-g minimum); vancomycin doses no. 3 and 4 were adjusted in an attempt to maintain the trough serum vancomycin level at greater than 12 mg/L. Nine peritonitis episodes complicated by a relapse were identified. Peritonitis episodes preceding a relapse were similar to relapse-free episodes with respect to patient age, diabetes, peritoneal dialysis modality, duration of peritoneal dialysis treatment, residual urea clearance, peritoneal fluid cell count, causative organism, and weekly vancomycin dose. However, cumulative 4-week mean trough vancomycin levels were consistently lower during peritonitis episodes preceding a relapse (7.8 +/- 0.6 mg/L during relapse-prone episodes v 13.7 +/- 0.9 mg/L during relapse-free episodes; P = 0.0004). Furthermore, relapses developed during nine of 14 peritonitis episodes demonstrating a 4-week mean trough vancomycin level less than 12 mg/L compared with zero of 17 episodes with a 4-week trough level greater than 12 mg/L (P < 0.05). The detection of a low initial 7-day trough vancomycin level also was a useful marker for subsequent peritonitis relapse. In 13 peritonitis episodes associated with an initial trough level less than 9 mg/L, nine were complicated by a relapse. The mean trough vancomycin level persisted below 9 mg/L over the final 3 weeks of therapy in all nine relapse-prone episodes as opposed to only one of four relapse-free episodes. All peritonitis relapses were treated successfully with 4 weeks of intravenous vancomycin therapy. This coincided with a significantly higher 4-week mean trough vancomycin level during treatment of the relapses (14.7 +/- 0.7 mg/L during the relapse v 7.8 +/- 0.6 mg/L immediately preceding the relapse; P < 0.05) despite similar mean weekly vancomycin dosages during both periods (19.4 +/- 1.0 mg/kg during the relapse v 17.8 +/- 1.2 mg/kg prior to the relapse; P = NS). In patients with uncomplicated peritoneal dialysis-related gram-positive peritonitis treated with weekly intravenous vancomycin, we conclude that (1) a suboptimal trough serum vancomycin level (cumulative 4-week trough serum vancomycin level <12 mg/L or an initial 7-day trough serum level <9 mg/L) is the only clinical parameter that identified peritonitis episodes at risk for relapse, and that (2) on detection of a suboptimal initial trough level (<9 mg/L), prevention of a subsequent peritonitis relapse may be possible if adequate trough vancomycin levels (>9 mg/L and preferably >12 mg/L) can be maintained for the remainder of therapy. (C) 1995 by the National Kidney Foundation, Inc.