Preferable timing of therapeutic drug monitoring in patients with impaired renal function treated with once-daily administration of vancomycin

Abstract

The aim of this study was to investigate the timing of therapeutic drug monitoring (TDM) in patients with impaired renal function treated with once-daily administration of vancomycin (VCM). Once-daily administration was selected for patients whose creatinine clearance (Ccr) was <80ml/min. TDM was conducted on day 3 or on day 4. Adult patients whose VCM dosage was not altered according to initial C min and for whom subsequent follow-up TDM was performed within 1week were entered into the study. Patients whose renal function deteriorated at follow-up TDM were excluded. One hundred sixty-five patients were eligible for analysis. Among patients with once-daily dosing, relative increases of C min at follow-up TDM compared with initial TDM were 34.5±39.2% in TDM on day 3 and 16.6±20.6% in TDM on day 4 (P=0.016). In contrast, there was no significant difference in the relative increase of C min between TDM on days 3 and 4 (26.1±39.6 vs. 18.4±25.6%, P=0.551) in the twice-daily regimen. On multivariate analysis, TDM on day 3 alone (odds ratio, 4.93; 95% confidence interval, 1.71-14.2) was selected as an independent risk factor associated with a relative increase of C min by >30% in the once-daily regimen. Steady-state VCM serum concentration was not achieved on day 3 in the once-daily regimen in patients with impaired renal function, and TDM on day 3 caused underestimation of C min.