Novel tool for vancomycin dosing could provide multiple benefits

Abstract

Pharmacists at Detroit Medical Center (DMC) led a research study that could help patients achieve targeted trough concentrations of vancomycin while at the same time reducing a pharmacist's workload. The research team wanted to validate a novel vancomycin dosing table for adult patients on continuous renal replacement therapy (CRRT). CRRT is commonly used to provide renal support in hemodynamically unstable, critically ill patients with renal failure. Their study found that for CRRT patients who were scheduled on vancomycin using the dosing tool, 58% were in the targeted range of achieving trough level concentrations of 15 to 20 mcg/mL, whereas only 37% of the patients who were dosed by levels were in that targeted range. When levels within 1 standard deviation of the target range were included, the trough levels for patients on scheduled vancomycin within target range increased to 89%. “The patients who were scheduled on vancomycin achieved the target level of 15 to 20 mcg/mL of vancomycin more than the patients who were dosed by levels,” said Merna Azuz, PharmD, who helped lead the research at Harper-Hutzel Hospital, which is part of DMC. “This was a very important conclusion since patients who were scheduled did not have to get as many levels drawn and they didn’t have to have as many notes entered by a pharmacist.” Consequently, the tool was saving pharmacists time because every level that is drawn has to be entered into the record. Azuz said they also found that CRRT patients should be given a loading dose of 25 mg/kg and not 20 mg/kg, as was the case previously. “Patients who are critically ill do have a higher volume of distribution, so giving a loading dose of 20 mg/kg was not achieving adequate levels,” she said. “In our new dosing table, we recommend patients be given a loading dose of 25 mg/kg.” Guidelines for dosing vancomycin prior to the study in this particular patient population suggest using a loading dose for patients of approximately 20 mg/kg, which targets a peak concentration of 25 to 30 mcg/mL. After that initial dose, the protocol at DMC is to base subsequent dosing on vancomycin serum monitoring every 12 to 48 hours. Different institutions have different protocols and different modalities. “This research was meant to provide guidance for pharmacists for dosing vancomycin in critically ill patients that are on CRRT,” said Azuz. Limited literature is available to guide clinicians on dosing antimicrobials during CRRT. Patients on CRRT experience life threatening infections with high mortality rates and require optimal dosing of antimicrobials. “This vancomycin table that we came up with actually looked at patient parameters, including patients’ weight, and it looked at the continuous fluid replacement rate that was being used for the patient,” Azuz said. “What we found out was that patients who had a higher replacement fluid rate were clearing the vancomycin more quickly than patients who had a lower replacement fluid rate. Based on that ultra-filtration rate, we came up with the vancomycin dose as well as the frequency at which the doses should be given.” The research provides valuable information for clinicians and more guidance on dosing patients on vancomycin therapy, said Azuz. “However, it is very important to note that this vancomycin dosing guide is solely a guide, it should not be mandatory, and it should not supersede the pharmacist's clinical judgement,” she said. The research is a testament to how pharmacists can be involved in potential policy changes at their respective institutions. Azuz was a resident at DMC from 2019 to 2020 and helped complete the second phase of the research project. Results have been presented to various committees at DMC with the ultimate goal of implementing the tool into hospital policy. Azuz is currently a clinical pharmacist at Ascension St. John Hospital in Detroit. The research was also presented at last year's American College of Clinical Pharmacy's virtual annual meeting.