ABSTRACT
Aims: To evaluate the value of therapeutic drug monitoring (TDM) of vancomycin in clinical practice. Methods: To review retrospectively on 292 hospital cases (111 females, 181 males) treated with vancomycin, July to October 2014, at ChoRay Hospital. The main evaluating parameters were TDM criteria for vancomycin (dose, dosing interval, times of monitoring), trough level, dose adjustment, renal function follow-up, minimum inhibitory concentration of infectious agents, clinical response. Results: Two hundred seventy-five patients (94.2%) received routine dose of 1 g vancomycin per IV infusion time. Dosing interval was given correctly to estimated glomerular filtration rate (eGFR) level 80.8% (235/291). The 1st monitoring after 9th dose was in 139 cases (47.6%). Trough level was lower than 10 mg/L in 86 patients (29.5%), higher than 20 mg/L in 96 (32.9%), and 110 in optimal range 10-20 mg/L (37.7%). Age and eGFR were 2 independent predictors for trough level. Dose adjustment were done in 6.9% (6/86) patients ≤ 10 mg/L, 20.8% (20/96) ones >20 mg/L, and 11.8% (13/110) ones 10-20 mg/L. Vancomycin concentrations in young patients were lower than those in elderly ones with OR = 5.9 [95%CI: 2.6 – 14.0], p = 0.0001. Response sensitivity was 69.3% (13/19) for dose reduction, and 83.3% (5/6) for dose increase. Dose adjustment did not make change in trough level compared to unadjusted ones. Nephrotoxicity rate was found as 8.4%. Treatment failure was 50% in patients with trough concentration/minimum inhibition concentration ratio ≤ 10 compared to 15% in ones with higher ratio > 10, p = 0.034. The failure rate was highest in patients received vancomycin ≤ 7 days (22/70: 31.4%), OR: 4 (2.0-7.7) p=0.002. The clinical AUC/MIC ratio cut-off, 190 mg/L/day, had 75.9% and 66.7%, respectively for sensitivity and specificity to predict the success result in treatment. Conclusion: The criteria of TDM on vancomycin were not applied strictly, especially for dosing intervals, dosing adjustment and follow-up thereafter. The clinical pharmacodynamics of vancomycin is dependent on both concentration and duration of treatment.