Impact of Serum Cystatin C-Based Glomerular Filtration Rate Estimates on Drug Dose Selection in Hospitalized Patients

Drug stewardship in chronic kidney disease to achieve effective and safe medication use

People living with chronic kidney disease (CKD) often experience multimorbidity and require polypharmacy. Kidney dysfunction can also alter the pharmacokinetics and pharmacodynamics of medications, which can modify their risks and benefits; the extent of these changes is not well understood for all situations or medications. The principle of drug stewardship is aimed at maximizing medication safety and effectiveness in a population of patients through a variety of processes including medication reconciliation, medication selection, dose adjustment, monitoring for effectiveness and safety, and discontinuation (deprescribing) when no longer necessary. This Review is aimed at serving as a resource for achieving optimal drug stewardship for patients with CKD. We describe special considerations for medication use during pregnancy and lactation, during acute illness and in patients with cancer, as well as guidance for the responsible use of over-the-counter drugs, herbal remedies, supplements and sick-day rules. We also highlight inequities in medication access worldwide and suggest policies to improve access to quality and essential medications for all persons with CKD. Further strategies to promote drug stewardship include patient education and engagement, the use of digital health tools, shared decision-making and collaboration within interdisciplinary teams. Throughout, we position the person with CKD at the centre of all drug stewardship efforts.

Toward Equitable Kidney Function Estimation in Critical Care Practice: Guidance From the Society of Critical Care Medicine's Diversity, Equity, and Inclusion in Renal Clinical Practice Task Force

OBJECTIVES

Accurate glomerular filtration rate (GFR) assessment is essential in critically ill patients. GFR is often estimated using creatinine-based equations, which require surrogates for muscle mass such as age and sex. Race has also been included in GFR equations, based on the assumption that Black individuals have genetically determined higher muscle mass. However, race-based GFR estimation has been questioned with the recognition that race is a poor surrogate for genetic ancestry, and racial health disparities are driven largely by socioeconomic factors. The American Society of Nephrology and the National Kidney Foundation (ASN/NKF) recommend widespread adoption of new "race-free" creatinine equations, and increased use of cystatin C as a race-agnostic GFR biomarker.

DATA SOURCES

Literature review and expert consensus.

STUDY SELECTION

English language publications evaluating GFR assessment and racial disparities.

DATA EXTRACTION

We provide an overview of the ASN/NKF recommendations. We then apply an Implementation science methodology to identify facilitators and barriers to implementation of the ASN/NKF recommendations into critical care settings and identify evidence-based implementation strategies. Last, we highlight research priorities for advancing GFR estimation in critically ill patients.

DATA SYNTHESIS

Implementation of the new creatinine-based GFR equation is facilitated by low cost and relative ease of incorporation into electronic health records. The key barrier to implementation is a lack of direct evidence in critically ill patients. Additional barriers to implementing cystatin C-based GFR estimation include higher cost and lack of test availability in most laboratories. Further, cystatin C concentrations are influenced by inflammation, which complicates interpretation.

CONCLUSIONS

The lack of direct evidence in critically ill patients is a key barrier to broad implementation of newly developed "race-free" GFR equations. Additional research evaluating GFR equations in critically ill patients and novel approaches to dynamic kidney function estimation is required to advance equitable GFR assessment in this vulnerable population.

Retrospective Evaluation of Cystatin C as a Measure of Renal Function in Pediatric Hematopoietic Stem Cell Transplant Patients Receiving Foscarnet for Cytomegalovirus Reactivation

BACKGROUND

Cytomegalovirus (CMV) infection following allogeneic hematopoietic cell transplantation has considerable morbidity and mortality, and foscarnet is a treatment option that requires renal dose adjustment. Serum creatinine (SCr)-based estimated glomerular filtration rate (eGFR) equations are used to estimate renal function for patients receiving foscarnet, but cystatin C (cysC) has been shown as a possible alternative. Data examining cysC-based eGFR in this population is sparse. Our primary objective was to evaluate outcomes of patients treated with foscarnet dosed utilizing cysC-based eGFR versus SCr-based eGFR.

METHODS

We analyzed patients on the transplantation and cellular therapies service at Memorial Sloan Kettering Kids from January 2011 to September 2021 who received allogeneic hematopoietic cell transplantation and ≥14 days of foscarnet for CMV infection. Patients with cysC-based eGFR were compared to a historical cohort of patients who only had SCr-based eGFR. Outcomes included time to CMV clearance, death or change in anti-CMV therapy. Cumulative incidence curves and cause-specific hazards model were used for analysis.

RESULTS

In 61 analyzed patients, no differences were found between the cohorts in cumulative incidence of change in anti-CMV therapy ( P = 0.17) or death ( P = 0.69). After adjustment for multiple confounders, patients in the SCr cohort seemed to have a higher chance of CMV clearance compared with the cysC cohort, but the difference was not statistically significant (hazard ratio = 2.42, P = 0.089). Patients who received corticosteroids appeared to have lower incidence of CMV clearance ( P = 0.056).

CONCLUSIONS

We did not find differences in outcomes when dosing foscarnet using cysC versus SCr for treatment of CMV infection.

Population pharmacokinetic model of cefepime for critically ill adults: a comparative assessment of eGFR equations

Cefepime exhibits highly variable pharmacokinetics in critically ill patients. The purpose of this study was to develop and qualify a population pharmacokinetic model for use in the critically ill and investigate the impact of various estimated glomerular filtration rate (eGFR) equations using creatinine, cystatin C, or both on model parameters. This was a prospective study of critically ill adults hospitalized at an academic medical center treated with intravenous cefepime. Individuals with acute kidney injury or on kidney replacement therapy or extracorporeal membrane oxygenation were excluded. A nonlinear mixed-effects population pharmacokinetic model was developed using data collected from 2018 to 2022. The 120 included individuals contributed 379 serum samples for analysis. A two-compartment pharmacokinetic model with first-order elimination best described the data. The population mean parameters (standard error) in the final model were 7.84 (0.24) L/h for CL1 and 15.6 (1.45) L for V1. Q was fixed at 7.09 L/h and V2 was fixed at 10.6 L, due to low observed interindividual variation in these parameters. The final model included weight as a covariate for volume of distribution and the eGFRcr-cysC (mL/min) as a predictor of drug clearance. In summary, a population pharmacokinetic model for cefepime was created for critically ill adults. The study demonstrated the importance of cystatin C to prediction of cefepime clearance. Cefepime dosing models which use an eGFR equation inclusive of cystatin C are likely to exhibit improved accuracy and precision compared to dosing models which incorporate an eGFR equation with only creatinine.

Sepsis-associated acute kidney injury: consensus report of the 28th Acute Disease Quality Initiative workgroup

Sepsis-associated acute kidney injury (SA-AKI) is common in critically ill patients and is strongly associated with adverse outcomes, including an increased risk of chronic kidney disease, cardiovascular events and death. The pathophysiology of SA-AKI remains elusive, although microcirculatory dysfunction, cellular metabolic reprogramming and dysregulated inflammatory responses have been implicated in preclinical studies. SA-AKI is best defined as the occurrence of AKI within 7 days of sepsis onset (diagnosed according to Kidney Disease Improving Global Outcome criteria and Sepsis 3 criteria, respectively). Improving outcomes in SA-AKI is challenging, as patients can present with either clinical or subclinical AKI. Early identification of patients at risk of AKI, or at risk of progressing to severe and/or persistent AKI, is crucial to the timely initiation of adequate supportive measures, including limiting further insults to the kidney. Accordingly, the discovery of biomarkers associated with AKI that can aid in early diagnosis is an area of intensive investigation. Additionally, high-quality evidence on best-practice care of patients with AKI, sepsis and SA-AKI has continued to accrue. Although specific therapeutic options are limited, several clinical trials have evaluated the use of care bundles and extracorporeal techniques as potential therapeutic approaches. Here we provide graded recommendations for managing SA-AKI and highlight priorities for future research.

Traditions and innovations in assessment of glomerular filtration rate using creatinine to cystatin C

PURPOSE OF REVIEW

Glomerular filtration rate (GFR) is the best index for kidney function and estimated GFR (eGFR) calculated from endogenous filtration markers like serum creatinine and cystatin C is widely used in clinical practice for chronic kidney disease diagnosis and prognostication. We sought to review the evolution of GFR estimating equations, nuances of eGFR interpretation, and utility of eGFR in drug dosing.

RECENT FINDINGS

The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) serum creatinine eGFR equation was recently updated to exclude the race variable and the CKD-EPI creatinine-cystatin C equation demonstrated the highest reliability. Although calculated creatinine clearance by Cockcroft Gault has been traditionally used for drug dosing, the use of eGFR is slowly being adapted by the Food and Drug Administration for pharmacokinetic studies. However, the individual-level accuracy of eGFR using the CKD-EPI 2021 equations remained low, with the distribution of measured GFR at a given eGFR value spanning several CKD stages.

SUMMARY

Although current methods of estimating GFR have improved in population measures of reliability, all have significant individual-level inaccuracies that can be an issue when clinical decision-making is contingent on the actual level of GFR. Modern methods of GFR measurements should be made widely available to enhance individualized patient decision-making.

Kidney Function Assessment in African American Patients: A Narrative Review for Pharmacists

Recent recognitions of longstanding societal inequity in kidney function assessments have prompted the call to eliminate race as part of the algorithm to assess estimated glomerular filtration rate (eGFR). Previous equations for eGFR estimation adopted race as part of the calculation. Incorporating race within eGFR equations results in overestimating and underestimating Black and nonblack patients, respectively. The inclusion of race is controversial. In September 2021, the National Kidney Foundation (NKF) and the American Society of Nephrology (ASN) combined task force recommended estimating the kidney function without using a race variable. The task force endorsed race-free creatinine-cystatin C equations to be more accurate than the creatinine-only equations. Before the application of NKF-ASN revised recommendations, major healthcare disparities influenced daily clinical practice. Those disparities include the delay in initiating medications that have reanl or cardio-protective effects, such as sodium-glucose cotransporter–2 inhibitors (SGLT-2i) and angiotensin-converting enzyme inhibitors (ACEIs). Clinical judgment should be employed when dose adjusting medications. Combining the eGFR with other clinical assessment tools such as urinary output, the expanded use of confirmatory tests, and the eGFR trend is suggested for a better kidney function assessment. Additionally, creatinine-cystatin C is recommended when feasible, and when institutions have the laboratory abilities.

Cystatin C: A Primer for Pharmacists

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.

Creatinine: From physiology to clinical application

Estimating static kidney function accurately and detecting changes in kidney function in a timely fashion are challenging but critically important tasks. Serum creatinine is the most widely used functional biomarker of the kidney. However, its use is associated with substantial shortcomings. Understanding these shortcomings is critical in allowing accurate interpretation of creatinine values and translating them into changes in kidney function. In this review, the pathways involved in creatinine generation and metabolism as well as the techniques involved in measuring creatinine concentrations are discussed. This allows for the discussion of the value and pitfalls in using creatinine as a marker of kidney function. In addition, information regarding alternative functional biomarkers of the kidney is provided.

Differences in Kidney Function Estimates Based on Creatinine and/or Cystatin C in Non-Traumatic Amputation Patients and Their Impact on Drug Prescribing

Accurate kidney function estimates are necessary when prescribing renally-eliminated medications. Our objectives were to investigate how amputation affects estimated glomerular filtration rate (eGFR) and to determine if dosing recommendations differ among different eGFR equations. In a cohort study of non-traumatic amputation patients, eGFR based on creatinine and/or cystatin C were measured before and after amputation. Prescribed, renally-eliminated medications were compared with dosing guidelines in Renbase^®. Data from 38 patients with a median age of 75 years were analyzed. The median (range) eGFR was 65 (15⁻103), 38 (13⁻79), and 48 (13⁻86) mL/min/1.73 m² before amputation and 80 (22⁻107), 51 (13⁻95), and 62 (16⁻100) mL/min/1.73 m² after amputation for eGFR_Creatinine, eGFR_CystatinC, and eGFR_Combined, respectively (p < 0.01). From before to after amputation, eGFR increased on average by 8.5, 6.1, and 7.4 mL/min/1.73 m² for eGFR_Creatinine, eGFR_CystatinC, and eGFR_Combined (all p < 0.01), respectively. At least one renally-eliminated medication was prescribed at a higher dose than recommended in 37.8% of patients using eGFR_CystatinC, 17.6% using eGFR_Combined and 10.8% using eGFR_Creatinine. In conclusion, amputation affects eGFR regardless of the eGFR equations. The differences among equations would impact prescribing of renally-eliminated medications, particularly when switching from creatinine to cystatin C.