Implications of Vancomycin Troughs Drawn Earlier Than Current Guidelines

Potentially eligible patients were identified via a Computerized Patient Records System (CPRS) search for laboratory vancomycin level measurements. The search supplied the researcher with the patient name, vancomycin level date and time, type of vancomycin level (trough or random), and vancomycin concentration. With this information, further data were gathered through CPRS: demographics, type of clinical infection, desired trough level (inferred if not listed in CPRS note), and vancomycin administration time (through the bar code medication administration system [BCMA] in CPRS). This analysis was of troughs, and multiple troughs may have originated from the same patient.

An early trough was defined as a trough taken more than 2 hours earlier than the next theoretical administration time or anytime before the third dose. After a trough was determined to be early or on time, the clinical actions taken during the dosing interval following sample collection were documented. A dose was considered to be held if stated in the BCMA or in a CPRS provider note. A dose was considered to be decreased with a change in frequency or strength that resulted in an overall daily dose decrease. A recollected vancomycin trough was counted within 24 hours of the trough or per a note in CPRS. Finally, observations that noted trends in vancomycin trough management were recorded.

The chi-square test with a significance criterion of 0.05 was used to compare early and on time troughs. Based on the results from the Boston, Massachusetts, study and 1 other study, about 780 vancomycin troughs would be required to meet significance in the primary outcome. ^5,6

Results

A total of 474 patient charts were reviewed, and 278 met inclusion criteria (196 were excluded). Of the included patients, 799 trough levels were analyzed. Of these, 377 (42.2%) were drawn early. There was no significant difference in the baseline characteristics of the early group vs the correctly timed group (Table 1). Of the early troughs, 190 (56.3%) were drawn prior to the third dose of vancomycin. It was observed that a large portion of these troughs occurred after a vancomycin dose adjustment.

Clinical actions taken after sampling occurred at a rate of 14.5% in the early group and 22.9% in the correctly timed group ( P = .003; Table 2). Early troughs led to a 7.7% rate of trough recollection, which was significantly greater than the 1.5% rate in the correctly timed group ( P < .001). An analysis of each factor resulting in a clinical action illustrated that the rates of daily dose decrease and discontinued dose were similar between the groups (Table 3). However, the rate of held doses was 8.3% in the early group and 17.1% in the correctly timed group.

This research process yielded some observations. Occasionally a trough was drawn after vancomycin therapy was discontinued and when there was no concern for nephrotoxicity. After the guidelines were published, providers continued to document in CPRS notes to check troughs before the third dose. This incidence decreased over time. Troughs were taken often in patients who were receiving a short course of therapy or who were hemodynamically stable. Finally, documentation of vancomycin regimen changes occasionally did not match the record in the BCMA (in these situations, the BCMA record was used for this study).