Relationship between vancomycin trough concentration and 24-h area under the curve concentration in Tunisian patients

The 24-h area under the curve concentration (AUC24 h) is associated with better clinical and bacteriological response to vancomycin in patients with methicillin-resistant Staphylococcus aureus who achieve the target AUC24 h between 400 and 700 mg×h/L. Recent consensus recommends maintaining trough concentrations between 15 and 20 mg/mL as a convenient target to reach an AUC/minimum inhibitory concentration (MIC) ≥ 400. The aim of this study was to determine the correlation between a calculated AUC24 h and a measured trough vancomycin concentration (C0). We conducted a retrospective observational study. Hospitalized patients prescribed vancomycin for a presumed or documented invasive staphylococcal infections were evaluated. A formula based on the relationship between dose, vancomycin clearance and creatinine clearance was used to determine each patient's AUC24 h. 161 patients were included in the study. Median age was 34 years. The mean daily dose of vancomycin was 28 mg/kg/day. The median vancomycin C0 was 12.2 mg/mL, 17.3% were in the therapeutic range. The median AUC was 246.84 mg×h/L, only 8% achieved the target AUC24 h between 400 and 700 mg×h/L. Of these, 3 patients had C0 between 15 and 20 mg/mL and 9 patients had C0> 20 mg/mL. A poor correlation was found between C0 and AUC24 h = 0.37; r2 = 0.14; p<0.0001. In conclusion, vancomycin C0 correlated poorly with AUC24/MIC targets. C0 seems to underestimate AUC24 h. So, a patient specific AUC24/MIC may serve to predict efficacy while C0 can be used as indicators of possible nephrotoxicity and development of resistance. Key words: Vancomycin, area under the curve (AUC), trough concentration, minimum inhibitory concentration, therapeutic drug monitoring.