Clinical practice guidelines for initiation and therapeutic drug monitoring, but not timing, of vancomycin dosing exist at many institutions. Scheduling vancomycin trough measurements and doses around the morning blood sample collection could yield more interpretable troughs and increase patient safety.To evaluate the appropriateness of blood sample collection times for vancomycin trough measurements before and after an initiative to change the timing of blood sampling to determine vancomycin doses and trough levels in a medical intensive care unit.A retrospective cohort study was conducted of patients in a medical intensive care unit who received intravenous vancomycin at a scheduled interval. Differences in continuous and categorical data were compared between pre- and postintervention groups. The primary outcome was proportion of blood samples collected for vancomycin trough measurements within 30 minutes of the next scheduled vancomycin dose.Baseline characteristics were similar between the preintervention (n = 68) and postintervention (n = 176) groups except for the percentage of blood samples drawn for trough measurements and morning laboratory tests (6% vs 81%; < .001). Frequency of loading doses was similar between patients in the pre- and postintervention groups, as was weight-based maintenance dosing. There was no significant difference in the percentage of blood samples collected to measure vancomycin trough levels appropriately at 30, 60, or 75 minutes from the next scheduled dose.Measuring vancomycin trough levels in morning blood samples did not affect the percentage of inappropriately collected blood samples used to measure vancomycin trough levels.