De-indexed estimated glomerular filtration rates: A simple step towards improving accuracy of drug dosing of renally excreted medications in moderate to severe obesity

De-indexed estimated glomerular filtration rates for the dosing of oral antidiabetic drugs in patients with chronic kidney disease

Introduction: Adjusting drug dose levels based on equations that standardize the estimated glomerular filtration rate (eGFR) to a body surface area (BSA) of 1.73 m2 can pose challenges, especially for patients with extremely high or low body mass index (BMI). The objective of the present study of patients with CKD and diabetes was to assess the impact of deindexing creatinine-based equations on estimates of kidney function and on the frequency of inappropriate prescriptions of oral antidiabetic drugs (OADs). Methods: The prospective CKD-REIN cohort is comprised of patients with eGFR <60 mL/min/1.73 m2. The inclusion criteria for this study were the use of OADs and the availability of data on weight, height and serum creatinine. We compared data for three BMI subgroups (group 1 <30 kg/m2; group 2 30-34.9 kg/m2; group 3 ≥35 kg/m2). Inappropriate prescriptions (contraindicated or over-dosed drugs) were assessed with regard to the summary of product characteristics and the patient's kidney function estimated with the 2009 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, the 2021 CKD-EPI equation, the Modification of Diet in Renal Disease (MDRD) equation, the European Kidney Function Consortium (EKFC) equation, their deindexed estimates, and the Cockcroft-Gault (CG) formula. The impact of deindexing the equations was evaluated by assessing 1) the difference between the indexed and deindexed eGFRs, and 2) the difference in the proportion of patients with at least one inappropriate OAD prescription between the indexed and deindexed estimates. Results: At baseline, 694 patients were receiving OADs. The median BMI was 30.7 kg/m2, the mean BSA was 1.98 m2, and 90% of patients had a BSA >1.73 m2. Deindexing the kidney function estimates led to higher eGFRs, especially in BMI group 3. The proportion of patients with at least one inappropriate prescription differed greatly when comparing indexed and deindexed estimates. The magnitude of the difference increased with the BMI: when comparing BMI group 1 with BMI group 3, the difference was respectively -4% and -10% between deindexed 2021 CKD-EPI and indexed CKD-EPI. Metformin and sitagliptin were the most frequent inappropriately prescribed OADs. Conclusion: We highlight significant differences between the BSA-indexed and deindexed versions of equations used to estimate kidney function, emphasizing the importance of using deindexed estimates to adjust drug dose levels - especially in patients with an extreme BMI.

Obesity Pillars Roundtable: Body mass index and body composition in Black and Female individuals. Race-relevant or racist? Sex-relevant or sexist?

Background

Body mass index (BMI or weight in kilograms/height in meters2) is the most common metric to diagnose overweight and obesity. However, a body composition analysis more thoroughly assesses adiposity, percent body fat, lean body mass (i.e., including skeletal muscle), and sometimes bone mineral density. BMI is not an accurate assessment of body fat in individuals with increased or decreased muscle mass; the diagnostic utility of BMI in individuals is also influenced by race and sex.

Methods

Previous Obesity Pillars Roundtables addressed the diagnostic limitations of BMI, the importance of android and visceral fat (especially among those with South and East Asian ancestry), and considerations of obesity among individuals who identify as Hispanic, diverse in sexual-orientation, Black, Native American, and having ancestry from the Mediterranean and Middle East regions. This roundtable examines considerations of BMI in Black and female individuals.

Results

The panelists agreed that body composition assessment was a more accurate measure of adiposity and muscle mass than BMI. When it came to matters of race and sex, one panelist felt: "race is a social construct and not a defining biology." Another felt that: "BMI should be a screening tool to prompt further evaluation of adiposity that utilizes better diagnostic tools for body composition." Regarding bias and misperceptions of resistance training in female individuals, another panelist stated: "I have spent my entire medical career taking care of women and have never seen a woman unintentionally gain 'too much' muscle mass and bulk up from moderate strength training."

Conclusions

Conveying the importance of race and sex regarding body composition has proven challenging, with the discussion sometimes devolving into misunderstandings or misinformation that may be perceived as racist or sexist. Body composition analysis is the ultimate diagnostic equalizer in addressing the inaccuracies and biases inherent in the exclusive use of BMI.

Entering the Third Decade After Kidney Transplantation: Excellent Graft Function Refers to Superior Graft but Not Patient Survival

Kidney transplant recipients (KTRs) with ultralong-term survival represent a growing, yet insufficiently studied patient cohort. In this single-center retrospective study, we analyzed 248 ultralong-term survivors (≥20 years). KTRs were classified into those with superior graft function (defined as eGFR ≥45 ml/min + proteinuria ≤300 mg/day + eGFR-slope ≤ 2 ml/min/1.73 m2/year) and inferior graft function regarding the risk of CKD progression. 20 years post-transplant, median eGFR was 54 ml/min (11-114), proteinuria 200 mg/24 h (0-7,620), eGFR decline 0.45 ml/min/1.73 m2/year (11.7 6.5) and DSA had been detected in 19.7% of KTRs. We identified 96 KTRs (38.7%) with superior (group 1) and 152 KTRs (61.3%) with inferior graft function (group 2). Donation after cardiac death, female sex, glomerulonephritis as primary disease, and early TCMR were independently associated with inferior graft function. Graft survival was significantly better in group 1 compared to group 2 (LogRank, p < 0.001). Besides group affiliation (HR 20.515, p = 0.003), multivariable analysis identified DSA development (HR 3.081, p = 0.023) and donor age (HR 1.032, p = 0.024) as independent factors. Interestingly, there was no significant difference in patient survival (LogRank, p = 0.350). In ultralong-term survivors, excellent graft function refers to superior graft survival but does not extend ultimate patient survival. DSA-formation should be taken seriously even in the ultralong-term.

Comparative Plasma and Interstitial Tissue Fluid Pharmacokinetics of Meropenem Demonstrate the Need for Increasing Dose and Infusion Duration in Obese and Non-obese Patients

BACKGROUND AND OBJECTIVES

A quantitative evaluation of the PK of meropenem, a broad-spectrum β-lactam antibiotic, in plasma and interstitial space fluid (ISF) of subcutaneous adipose tissue of obese patients is lacking as of date. The objective of this study was the characterisation of meropenem population pharmacokinetics in plasma and ISF in obese and non-obese patients for identification of adequate dosing regimens via Monte-Carlo simulations.

METHODS

We obtained plasma and microdialysate concentrations after administration of meropenem 1000 mg to 15 obese and 15 non-obese surgery patients from a prospective clinical trial. After characterizing plasma- and microdialysis-derived ISF pharmacokinetics via population pharmacokinetic analysis, we simulated thrice-daily (TID) meropenem short-term (0.5 h), prolonged (3.0 h), and continuous infusions. Adequacy of therapy was assessed by the probability of pharmacokinetic/pharmacodynamic (PK/PD) target attainment (PTA) analysis based on time unbound concentrations exceeded minimum inhibitory concentrations (MIC) on treatment day 1 (%fT _{> MIC}) and the sum of PTA weighted by relative frequency of MIC values for infections by pathogens commonly treated with meropenem. To avoid interstitial tissue fluid concentrations below MIC for the entire dosing interval during continuous infusions, a more conservative PK/PD index was selected (%fT _{> 4 × MIC}).

RESULTS

Adjusted body weight (ABW) and calculated creatinine clearance (CLCR_{CG_ABW}) of all patients (body mass index [BMI] = 20.5-81.5 kg/m²) explained a considerable proportion of the between-patient pharmacokinetic variability (15.1-31.0% relative reduction). The ISF:plasma ratio of %fT _{> MIC} was relatively similar for MIC ≤ 2 mg/L but decreased for MIC = 8 mg/L over ABW = 60-120 kg (0.50-0.20). Steady-state concentrations were 2.68 times (95% confidence interval [CI] = 2.11-3.37) higher in plasma than in ISF, supporting PK/PD targets related to four times the MIC during continuous infusions to avoid suspected ISF concentrations constantly below the MIC. A 3000 mg/24 h continuous infusion was sufficient at MIC = 2 mg/L for patients with CLCR_{CG_ABW} ≤ 100 mL/min and ABW < 90 kg, whereas 2000 mg TID prolonged infusions were adequate for those with CLCR_{CG_ABW} ≤ 100 mL/min and ABW > 90 kg. For MIC = 2 mg/L and %fT_{> MIC} = 95, PTA was adequate in patients over the entire investigated range of body mass and renal function using a 6000 mg continuous infusion. A prolonged infusion of meropenem 2000 mg TID was sufficient for MIC ≤ 8 mg/L and all investigated ABW and CLCR_{CG_ABW} when employing the PK/PD target %fT _{> MIC} = 40. Short-term infusions of 1000 mg TID were sufficient for CLCR_{CG_ABW} ≤ 130 mL/min and distributions of MIC values for Escherichia coli, Citrobacter freundii, and Klebsiella pneumoniae but not for Pseudomonas aeruginosa.

CONCLUSIONS

This analysis indicated a need for higher doses (≥ 2000 mg) and prolonged infusions (≥ 3 h) for obese and non-obese patients at MIC ≥ 2 mg/L. Higher PTA was achieved with prolonged infusions in obese patients and with continuous infusions in non-obese patients.

TRIAL REGISTRATION

EudraCT: 2012-004383-22.

Assessment of Kidney Function in Patients With Extreme Obesity: A Narrative Review

Objectives:

To discuss the evidence and caveats associated with estimated and measured creatinine clearance (eClCr and mClCr) and glomerular filtration rate (eGFR and mGFR) assessments of kidney function in patients with more extreme forms of obesity.

Data Sources:

PubMed (1976 to mid-May 2020) was used, with bibliographies of retrieved articles searched for additional articles.

Study Selection and Data Extraction:

Articles using gold standard mGFR to evaluate eClCr, mClCr, and eGFR assessments of kidney function in patients with more extreme forms of obesity were included.

Data Synthesis:

The overestimation of GFR by mClCr is well established, but mClCr is an alternative to mGFR assessments for determining medication dosing in patients with extremes of body size or muscle mass, or in patients receiving narrow therapeutic index medications when eGFR is likely to be inaccurate. The vast majority of studies comparing eGFR assessments with gold standard indicators of kidney function were attempts to validate eGFR equations for diagnosing and staging chronic kidney disease (CKD).

Relevance to Patient Care and Clinical Practice:

For dosing medications in patients with stable kidney function and extreme obesity, a deindexed 4-variable Modification of Diet in Renal Disease or CKD Epidemiology Collaboration equation is an alternative to Cockcroft-Gault. Consistent use of the same equation by provider and between providers within any given setting is of paramount importance.

Conclusions:

In patients with extreme obesity and stable kidney function, eClCr or eGFR using deindexed values provides estimates of function for dosing adjustments of medications with elimination by the kidneys, but more research is needed with respect to the best size descriptor to use with estimating equations.