Therapeutic drug monitoring of vancomycin: A retrospective cross-sectional study of blood draw timing and clinical outcomes

Therapeutic drug monitoring (TDM) is key to optimizing vancomycin therapy, as accurate sampling timing ensures valid drug levels and supports safe, effective clinical decisions. This study aimed to assess the timing accuracy of blood draws for vancomycin TDM, evaluate its clinical implications, and identify predictors of timing errors. A cross-sectional study was conducted at King Saud University Medical City, involving 103 patients from October 2023 to December 2023. The primary outcome was adherence to the blood sampling timing guidelines. Secondary outcomes included clinical cure rates, acute kidney injury incidence, and in-hospital mortality. Of the analyzed samples, 80.6% were improperly timed. Clinical cure rates were significantly higher among patients with correctly timed samples (75%) compared to those with incorrectly timed samples (57.83%). Timely sampling improved cure rates for pulmonary and skin infections (85.71%), while improper timing reduced them to 72.22% and 62.5%, respectively. Improper timing was linked to higher in-hospital mortality (30.12%) and acute kidney injury (15.66%). Multivariate analysis revealed that bacteremia significantly reduced the likelihood of clinical cure (odds ratio = 0.387, 95% confidence interval [0.160, 0.933], P = .035), while 3 times daily dosing significantly increased the odds of correctly timed samples (odds ratio = 5.1, 95% confidence interval [1.125, 23.11], P = .035). This study highlights the critical role of accurate timing in vancomycin TDM for achieving favorable patient outcomes and reducing adverse events. Strengthened institutional protocols and targeted training programs are essential to improve adherence to sampling guidelines and enhance patient safety.