Background <p>Despite numerous studies on safety, acute kidney injury (AKI) caused by vancomycin and/or gentamicin remains a persistent medical issue. However, it remains unclear whether vancomycin AUC below 600&#xa0;mg·h/L in combination with gentamicin trough level at least below 2&#xa0;µg/mL are reliable indices to reduce the risk of AKI in patients treated with concomitant vancomycin and gentamicin.</p> Objective <p>The aim was to elucidate the pharmacokinetic factors associated with AKI development in patients receiving concomitant use of vancomycin and gentamicin in the setting of therapeutic drug monitoring (TDM).</p> Methods <p>A retrospective study was conducted in 15 patients treated with concomitant vancomycin and gentamicin with TDM. The patients were classified into AKI group and no-AKI group. Vancomycin area under the curve (AUC), gentamicin trough levels, and duration of concomitant duration of vancomycin and gentamicin were investigated.</p> Results <p>Six (40%) of 15 patients developed AKI during the study period. In AKI group (<i>n</i> = 6), vancomycin AUC was significant higher [median (range) 561 (543‒712) mg·h/L compared to no-AKI group (<i>n</i> = 9), 380 (185‒600) mg·h/L, <i>p</i> = 0.026)], although no significant differences in gentamicin trough level and duration of concomitant vancomycin and gentamicin treatment were found between the two groups. Receiver operating characteristic analysis showed that the best cut-off vancomycin AUC for predicting AKI was 523&#xa0;mg·h/L, with AUC of 0.852, sensitivity of 1.000 and specificity of 0.778 (<i>p</i> = 0.025).</p> Conclusions <p>In patients treated with concomitant vancomycin and gentamicin with trough level below 1–2&#xa0;µg/mL, vancomycin AUC 530 − 600&#xa0;mg·h/L is associated with AKI risk.</p>