Introduction:
Vancomycin is of clinical importance because it is the last line of defence against bacteria.
Aim of the research: To compare serum levels of vancomycin before and after therapeutic drug monitoring (TDM) by a pharmacist in hospitalized patients.

Material and methods:
This prospective interventional study was performed on 30 patients admitted to the Infectious Disease Ward of Ahvaz Razi Hospital in 2019. In order to determine serum levels, peripheral blood samples were taken from patients in 2 stages (2 ml each time) before and 3 days after changing dose of vancomycin. For the patients, a checklist including demographic and clinical information (case number, gender, age, weight, underlying disease, site of infection, prescription dose, serum level, and type of microorganism) was completed.

Results:
The mean age of patients was 44.67 years and 53.3% were female. Serum level of the drug in 86.66% of patients did not correspond to the therapeutic range. In 33.33% of patients the dose based on weight and GFR did not correspond to the optimum dose, and in 86.66% of patients the serum was not at the desirable level. Overall, 26 patients recovered and were discharged, and 4 patients, who had an undesirable level of serum, died. The results of the study showed that by calculating the dose according to the initial criteria, it did not reach the desired level, and the presence of different diseases in patients receiving vancomycin and different drugs makes TDM necessary.

Conclusions:
Because there is not much time to intervene due to discharging patients or discontinuation of medication, designing a system to accelerate the TDM process is suggested.