Pharmacists are at the forefront of dosing and monitoring medications eliminated by or toxic to the kidney. To evaluate the effectiveness and safety of these medications, accurate measurement of kidney function is paramount. The mainstay of kidney assessment for drug dosing and monitoring is serum creatinine (SCr)-based estimation equations. Yet, SCr has known limitations including its insensitivity to underlying changes in kidney function and the numerous non-kidney factors that are incompletely accounted for in equations to estimate glomerular filtration rate (eGFR). Serum cystatin C (cysC) is a biomarker that can serve as an adjunct or alternative to SCr to evaluate kidney function for drug dosing. Pharmacists must be educated about the strengths and limitations of cysC prior to applying it to medication management. Not all patient populations have been studied and some evaluations demonstrated large variations in the relationship between cysC and GFR. Use of eGFR equations incorporating cysC should be reserved for drug management in scenarios with demonstrated outcomes, including to improve pharmacodynamic target attainment for antibiotics or reduce drug toxicity. This article provides an overview of cysC, discusses evidence around its use in medication dosing and in special populations, and describes practical considerations for application and implementation.

The use of the kidney function biomarker cystatin C (cysC) can improve the accuracy of vancomycin dosing for target trough attainment in non-obese patients. It is unknown whether cysC can also improve vancomycin target trough attainment in overweight and obese patients. We conducted a retrospective observational study of overweight or obese hospitalized adults with stable renal function administered intravenous vancomycin between January 2011 and July 2019. Linear regression models were used to predict initial steady-state vancomycin troughs using several factors, including various cysC- and serum creatinine (SCr)-based estimates of kidney function. We compared the predicted proportion of patients within the target trough range (10-20mg/L) using the derived models to that observed from usual care. Of the 200 included patients, the mean trough level was 15 ± 6.3 mg/L. The optimal model to predict the initial trough included both cysC and SCr (R²= 0.48) rather than either biomarker alone. This model predicted 79% (95% CI: 73%-85%) of troughs could be between 10 - 20mg/L compared to the 62% observed in clinical practice (p < 0.001), a 1.3-fold increase. This study is the first to examine the role of cysC in predicting vancomycin levels in an exclusively overweight or obese population. While dosing models based on cysC appear promising in this setting, prospective validation is needed.

Objective: The primary objective was to determine the rate of clinical actions taken post-discharge on updated microbiology results by an ID pharmacist-led team. Secondary objectives were to describe the microbiology results requiring intervention, characterize interventions by type and severity, and determine time from result to clinical review. Design: Retrospective cohort study. Setting: Four hospitals within Mayo Clinic, including two large academic centers and two Mayo Clinic Health System sites. Participants: Adult patients at four sites within Mayo Clinic from 1/1/2019 to 2/28/2023. Eligible patients had a hospitalization with an ID consult and an updated microbiology result reported after discharge. Intervention: Pharmacists reviewed a report of selected patients with microbiology tests that resulted post-discharge within the last 24–96 hours. Interventions were recorded electronically in real-time by the pharmacist. Of those patient encounters with an intervention, a sample of 200 patient encounters was randomly selected for detailed chart abstraction. Results: A total of 6,792 encounters with at least one microbiology result reviewed post-discharge were identified. Of these encounters, 1977 (29%) had at least one resulting intervention. Median time from test update to clinical review was 27.2 hours (IQR 21.6–69.6). The highest severity ratings, in which failure to intervene may have resulted in patient harm, were assigned to the intervention in 28% of cases. Conclusions: For patients seen by an inpatient ID consult service, a post-hospital discharge microbiology result review process performed by ID-trained pharmacists effectively addressed abnormal results during the transition of care. Similar processes may be considered at other institutions.