Illustration of why a trough level of 15 mg/L guarantees an AUC>400 . The area within the shaded green rectangle alone contributes an AUC of 15x24=360. The additional area under the peaks (the blue shaded area) will invariably push the AUC over 400. Time Vancomycin concentration - @PulmCrit 24 hours 15 mg/L Trough level = 15 mg/L