Predictive performance of ten equations for estimating creatinine clearance in cardiac patients. Iohexol Cooperative Study Group

Assessment of kidney function using inulin-based and estimated glomerular filtration rates before and after allogeneic hematopoietic stem cell transplantation in pediatric patients

BACKGROUND

Accurate evaluation of kidney function before and after allogeneic hematopoietic stem cell transplantation (allo-HSCT) is important for both informed decision making and detection of chronic kidney disease. However, to the best of our knowledge, no report has evaluated the glomerular filtration rate (GFR) in pediatric patients who underwent HSCT using the gold standard GFR measurement, as well as inulin-based GFR (iGFR).

METHODS

We assessed iGFR before and after allo-HSCT to evaluate the impact of allo-HSCT on GFR in a prospective cohort study of 17 pediatric patients. We also assessed the accuracy and bias of the values of estimated GFR (eGFR) calculated using serum creatinine (Cr), cystatin C (CysC), beta-2 microglobulin (β₂ MG), 24-h creatinine clearance (24hCcr), and the full chronic kidney disease in children (CKiD) index that combines Cr, CysC, and blood urea nitrogen-based equations with iGFR as a reference to identify the most reliable equation for GFR.

RESULTS

There was no significant difference between the values before and after allo-HSCT. CKiD CysC-, 24hCcr-, and full CKiD-based values showed good within 30% (P30) accuracy (80.6%, 79.3%, and 80.6%, respectively), but only 24hCcr and full CKiD had good mean bias (8.5% and 8.9%, respectively) and narrow 95% limits of agreement (-32.2 to 52.7 mL/min/1.73 m² and -29.3 to 47.4 mL/min/1.73 m² , respectively) compared with the corresponding iGFR.

CONCLUSION

There was no significant impact of allo-HSCT on GFR in our cohort. The most reliable equations for pediatric patients with allo-HSCT were eGFR-24hCcr and eGFR-full CKiD.

Performance of Glomerular Filtration Rate Estimating Equations Before and After Bariatric Surgery

Rationale & Objective

Evaluation of glomerular filtration rate (GFR) is challenging in adults undergoing bariatric surgery because creatinine and cystatin C levels are influenced by changes in muscle and fat mass. Additionally, indexing of GFR by body surface area (BSA) may by affected by decreases in BSA.

Study Design

Prospective observational study.

Setting & Participants

27 adults with body mass index (BMI) ≥ 35 kg/m² who underwent measurement of GFR before and after bariatric surgery.

Outcomes

Indexed and nonindexed GFRs measured (mGFRs) using plasma iohexol clearance, indexed and nonindexed estimated GFR (eGFR) based on levels of creatinine, cystatin C, or both from Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations.

Analytic Approach

Bias and percent of estimates within 20% and 30% of mGFR (P₂₀ and P₃₀) for estimating equations were examined.

Results

Mean presurgery BMI was 49.5 (SD, 9.4) kg/m², BSA was 2.42 (SD, 0.27) m², nonindexed mGFR was 117.3 (SD, 34.1) mL/min, and indexed mGFR was 84.1 (SD, 22.0) mL/min/1.73 m². After 6 months, mean BMI changed by –13.8 (95% CI, −15.9 to −11.8) kg/m², BSA by −0.30 (95% CI, −0.33 to −0.27) m², and nonindexed mGFR by −9.2 (95% CI, −17.2 to −1.1) mL/min, while indexed mGFR was unchanged at 5.1 (95% CI, −0.1 to 10.4) mL/min/1.73 m². Nonindexed eGFR_cr was unbiased (median bias, 5.0 [95% CI, −4.3 to 11.6] mL/min) before surgery, but overestimated mGFR (8.8 [95% CI, 1.8 to 16.9] mL/min) after surgery. Nonindexed eGFR_cys underestimated mGFR before (median bias, −12.1 [95% CI, −21.4 to −1.2] mL/min) and after surgery (−11.2 [95% CI, −21.8 to −7.3] mL/min). Nonindexed eGFR_cr-cys was unbiased before (median bias, −6.0 [95% CI, −11.0 to 1.0] mL/min) and after surgery (−2.0 [95% CI, −8.8 to 4.9] mL/min). Findings were similar for indexed eGFR compared with indexed mGFR.

Limitations

Small, mostly white sample.

Conclusions

Changes in indexed and nonindexed GFRs may be discordant after bariatric surgery in adults because of decreases in BSA. Indexed and nonindexed eGFR_cr-cys may be less biased than indexed or nonindexed eGFR_cr or eGFR_cys because of opposite biases in estimating mGFR.

Concordance of Vancomycin Population-Predicted Pharmacokinetics with Patient-Specific Pharmacokinetics in Adult Hospitalized Patients: A Case Series

BACKGROUND

Vancomycin empiric therapy is commonly dosed using clinical algorithms adapted from population-predicted pharmacokinetic parameters. However, precise dosing of vancomycin can be designed using patient-specific pharmacokinetic calculations.

OBJECTIVE

The objective of this study is to assess the correlational fit between vancomycin population-predicted and patient-specific pharmacokinetic parameters [elimination rate constant (K_e) and half-life (t_1/2)] in a case series of adult hospitalized patients.

METHODS

This is a single-center case series of hospitalized adult patients who received vancomycin, had creatinine clearance calculation for derivation of population-predicted pharmacokinetic parameters, and had two vancomycin concentrations for calculation of patient-specific pharmacokinetic parameters. The primary objective of this case series is to evaluate the correlation between population-predicted and patient-specific pharmacokinetic parameters. The secondary objectives of this study are to evaluate the mean bias and precision between the population-predicted and patient-specific pharmacokinetic parameters and to assess the correlation between population-predicted and patient-specific pharmacokinetic parameters in special population subgroups (obese patients with body mass index ≥ 30 kg/m² and patients with renal dysfunction). All correlation analyses were performed on the population-predicted pharmacokinetics using diverse methods of estimating renal function (Salazar-Corcoran and Cockcroft-Gault methods using either ideal, actual, or adjusted body weights). All significance testing was set at an α of < 0.05. IBM SPSS Statistics version 25 and SAS version 9.4 were used to conduct all statistical analyses.

RESULTS

A total of 30 patients were included in the study; 33.3% (10/30) of the patients were obese and 56.7% (17/30) had renal dysfunction. In all patients in the study, the calculated population-predicted K_e and t_1/2 using all four creatinine clearance estimation methods were each significantly correlated with patient-specific K_e and t_1/2 (all Pearson correlation coefficients [r]: > + 0.7, p < 0.001). The population-predicted K_e and t_1/2 calculated using Cockcroft-Gault creatinine clearance using adjusted body weight showed the strongest association with patient-specific K_e and t_1/2. In the subgroup analyses, all the population-predicted K_e and t_1/2 using four creatinine clearance estimation methods were each significantly correlated with patient-specific K_e and t_1/2. The exception was the population-predicted t_1/2 derived from Cockcroft-Gault creatinine clearance using actual body weight that did not show a significant correlation with patient-specific t_1/2 in obese patients.

CONCLUSIONS

In this case series, population-predicted pharmacokinetic parameters were strongly correlated with patient-specific pharmacokinetic parameters. The vancomycin population-predicted pharmacokinetic formula can be used safely to predict a patient's vancomycin pharmacokinetic disposition and can be maintained as an empiric dosing strategy in various hospitalized adult patients.

Comparison of methods to estimate glomerular filtration rate in paediatric oncology patients

AIMS

Glomerular filtration rate (GFR) is estimated daily in paediatric oncology patients; however, few equations, particularly ones that do not include serum creatinine, have been evaluated in this population. We aimed to compare the predictive performance of different equations available to estimate GFR in paediatric oncology patients.

METHODS

GFR was measured (mGFR) in paediatric oncology patients based on a chromium 51-labeled ethylene diamine tetraacetic acid excretion test. GFR was estimated (eGFR) in these same patients using equations identified from the literature. mGFR and eGFR values were compared, and the predictive performance of various eGFR equations was assessed in terms of their bias, precision and accuracy.

RESULTS

In total, 124 mGFR values ranging from 7 to 146 mL/min were available for analysis from 73 children. Twenty-two equations were identified from the literature. The Flanders metadata equation displayed the lowest absolute bias (mean error of 0.9 mL/min) and the greatest precision (root mean square error of 13.1 mL/min). The univariate Schwartz equation predicted the highest percentage (81.5%) of eGFR values within 30% of mGFR values, and the Rhodin fat-free mass equation predicted the highest percentage (37.1%) of eGFR values within 10% of mGFR values.

CONCLUSIONS

A number of equations were identified that could be used to estimate renal function in paediatric oncology patients; however, none was found to be highly accurate. The Flanders metadata equation and univariate Schwartz performed the best in this study, and we would suggest that these two equations may be used cautiously in paediatric oncology patients for clinical decision making, understanding their limitations.

Kidney Function in Obesity-Challenges in Indexing and Estimation

As the prevalence of obesity continues to increase worldwide, an increasing number of people are at risk for kidney disease. Thus, there is a critical need to understand how best to assess kidney function in this population, and several challenges exist. The convention of indexing glomerular filtration rate (GFR) to body surface area (BSA) attempts to normalize exposure to metabolic wastes across populations of differing body size. In obese individuals, this convention results in a significantly lower indexed GFR than unindexed GFR, which has practical implications for drug dosing. Recent data suggest that "unindexing" estimated GFR (multiplying by BSA/1.73 m2) for drug dosing may be acceptable, but pharmocokinetic data to support this practice are lacking. Beyond indexing, biomarkers commonly used for estimating GFR may induce bias. Creatinine is influenced by muscle mass, whereas cystatin C correlates with fat mass, both independent of kidney function. Further research is needed to evaluate the performance of estimating equations and other filtration markers in obesity, and determine whether unindexed GFR might better predict optimal drug dosing and clinical outcomes in patients whose BSA is very different than the conventional normalized value of 1.73 m2.

No role for patient body weight on renal function assessment for drug dosing

Objectives

To evaluate the ability of body-weight-driven renal function assessment (RFA) formulae to predict on-target elimination rate ranges for gentamicin in patients with varying degrees of renal function.

Methods

A 6 year retrospective pharmacokinetic study was conducted at a university teaching hospital.

Results

A total of 85 patients met the inclusion criteria and 127 pharmacokinetic files were analysed from patients on medical-surgical wards (53%) and medical-surgical ICUs (13%) receiving intravenous gentamicin for treatment, as well as those for patients receiving it for surgical prophylaxis (34%). Each RFA formula was examined against standard dosing tables for gentamicin. A table of acceptable elimination rates was generated using a traditional peak of 8 mg/L and trough between 0.5 and 2 mg/L associated with each of the dosing interval extensions. The ability of each RFA formula to select on-target elimination rates was evaluated. The RFA formula assuming a normalized body weight of 72 kg and a modified creatinine reagent adjustment factor of 90% provided the most accurate on-target elimination rate selection. This method was superior to dosing interval selection based on the Modification in Diet Renal Disease (MDRD) formula, Sanford's guide method, as well as the Cockcroft-Gault formulae using total body weight, ideal body weight or lean body weight ( P  <   0.0001).

Conclusions

Based on the use of gentamicin as a surrogate guide for renally adjusted drugs, these results support dosing interval selection based on a normalized body weight method and a formula reagent adjustment factor of 90% within the Cockcroft-Gault formula.

Applicability of the Schwartz Equation and the Chronic Kidney Disease in Children Bedside Equation for Estimating Glomerular Filtration Rate in Overweight Children

STUDY OBJECTIVE

To determine if significant correlations exist between glomerular filtration rate (GFR) prediction equation values, derived by using the original Schwartz equation and the Chronic Kidney Disease in Children (CKiD) bedside equation with a 24-hour urine creatinine clearance (Clcr ) value normalized to a body surface area of 1.73 m(2) in overweight and obese children.

DESIGN

Prospective analysis (20 patients) and retrospective analysis (43 patients).

SETTING

Pediatric inpatient ward and pediatric nephrology clinic at a comprehensive academic medical center.

PATIENTS

Sixty-three pediatric patients (aged 5-17 years), of whom 27 were overweight (body mass index [BMI] at the 85th percentile or higher) and 36 were not overweight (BMI lower than the 85th percentile [controls]) between 2007 and 2012.

METHODS AND MAIN RESULTS

Data from the overweight patients were compared with nonoverweight controls. GFR values were calculated by using the original Schwartz equation and the CKiD bedside equation. Each patient's 24-hour urine Clcr value normalized to a body surface area of 1.73 m(2) served as the index value. A Pearson correlation coefficient model was used to determine association between the 24-hour urine Clcr value (index value) with the Schwartz and CKiD GFR estimations. Significant correlation was found to exist between the Schwartz and CKiD bedside GFR estimations relative to the 24-hour urine Clcr in the control subjects (r = 0.85, p<0.0001, and r = 0.85, p<0.0001, respectively). Significant correlation was also found to exist between the Schwartz and CKiD bedside GFR values with the 24-hour urine Clcr value in overweight subjects (r = 0.86, p<0.0001, and r = 0.86, p<0.0001, respectively). The Schwartz equation estimated average GFR 21.75 ml/minute/1.73 m(2) higher than 24-hour urine Clcr (p<0.0001) in overweight children with a kidney disorder. The CKiD bedside GFR estimations were not significantly different compared with 24-hour urine Clcr values for the overweight group with kidney disorder (p=0.85).

CONCLUSION

The Schwartz and CKiD bedside estimations of GFR correlated with 24-hour urine Clcr values in both overweight and nonoverweight children. Compared with the Schwartz equation, which tended to overestimate renal function, the CKiD bedside equation appeared to approximate 24-hour urine Clcr more closely in overweight children with kidney disorder.

Hematological toxicity of carboplatin for gynecological cancer according to body mass index

PURPOSE

The aim of the present study was to analyze how patient weight affects the hematological toxicity of carboplatin and whether this toxicity is more prevalent in overweight patients.

METHODS

We performed a retrospective 2-year study of patients diagnosed with a gynecological cancer and whose treatment regimen contained carboplatin (AUC dose = 5 or 6) and paclitaxel (dose = 175 mg/m(2)) every 3 weeks (CP scheme). We recorded all severe hematological events (thrombocytopenia, neutropenia, and/or anemia grade III/IV) according to the CTCAE v4.03, as well as treatment modifications and the need for granulocyte colony-stimulating factors (G-CSF) and/or erythropoietin (EPO) or packed red blood cells (PRBC). Patients with a body mass index (BMI) ≥27 kg/m(2) were considered as overweight (OW) and those with a BMI <27 kg/m(2) were considered as normal weight (NW).

RESULTS

Fifty-two patients met the inclusion criteria (21 patients in the OW group, 31 patients in the NW group). The OW group showed a higher incidence of thrombocytopenia (95% confidence intervals (CI) 1.51-27.72; p < 0.02) and anemia (95% CI 1.06-33.63; p < 0.05). Moreover, this was reflected in a greater number of changes in the usual CP regimen (95% CI 2.19-44.32; p < 0.01). The need for G-CSF and/or EPO/PRBC was also significantly higher in the OW group (95% CI 1.08-12.16; p < 0.04).

CONCLUSIONS

Carboplatin dosing based on real weight in obese patients resulted in increased hematologic toxicity, mainly thrombocytopenia. Dose adjustment based on other descriptors of weight, such as adjusted weight, may be better tolerated by patients. However, future studies are needed to demonstrate not only better safety of carboplatin but also improved survival rates.

Accuracy of GFR estimating equations combining standardized cystatin C and creatinine assays: a cross-sectional study in Sweden

BACKGROUND

The recently established international cystatin C calibrator makes it possible to develop non-laboratory specific glomerular filtration rate (GFR) estimating (eGFR) equations. This study compares the performance of the arithmetic mean of the revised Lund-Malmö creatinine and CAPA cystatin C equations (MEANLM-REV+CAPA), the arithmetic mean of the Chronic Kidney Disease Epidemiology Collaboration equation (CKD-EPI) creatinine and cystatin C equations (MEANCKD-EPI), and the composite CKD-EPI equation (CKD-EPICREA+CYSC) with the corresponding single marker equations using internationally standardized calibrators for both cystatin C and creatinine.

METHODS

The study included 1200 examinations in 1112 adult Swedish patients referred for measurement of GFR (mGFR) 2008-2010 by plasma clearance of iohexol (median 51 mL/min/1.73 m2). Bias, precision (interquartile range, IQR) and accuracy (percentage of estimates ±30% of mGFR; P30) were compared.

RESULTS

Combined marker equations were unbiased and had higher precision and accuracy than single marker equations. Overall results of MEANLM-REV+CAPA/MEANCKD-EPI/CKD-EPICREA+CYSC were: median bias -2.2%/-0.5%/-1.6%, IQR 9.2/9.2/8.8 mL/min/1.73 m2, and P30 91.3%/91.0%/91.1%. The P30 figures were about 7-14 percentage points higher than the single marker equations. The combined equations also had a more stable performance across mGFR, age and BMI intervals, generally with P30 ≥90% and never <80%. Combined equations reached P30 of 95% when the difference between eGFRCREA and eGFRCYSC was <10% but decreased to 82% at a difference of ≥40%.

CONCLUSIONS

Combining cystatin C and creatinine assays improves GFR estimations with P30 ≥90% in adults. Reporting estimates of both single and combined marker equations in clinical settings makes it possible to assess the validity of the combined equation based on the agreement between the single marker equations.

Creatinine-based equations for the adjustment of drug dosage in an obese population

AIM

For drug dosing adaptation, the Kidney Disease: Improving Global Outcomes (KDIGO) guidelines recommend using estimated glomerular filtration rate (eGFR) by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation, after 'de-indexation' by body surface area (BSA). In pharmacology, the Cockcroft-Gault (CG) equation is still recommended to adapt drug dosage. In the context of obesity, adjusted ideal body weight (AIBW) is sometimes preferred to actual body weight (ABW) for the CG equation. The aim of the present study was to compare the performance of the different GFR-estimating equations, non-indexed or de-indexed by BSA for the purpose of drug-dosage adaptation in obese patients.

METHODS

We analysed data from patients with a body mass index (BMI) higher than 30 kg m(-2) who underwent a GFR measurement. eGFR was calculated using the CKD-EPI and Modification of Diet in Renal Disease (MDRD) equations, de-indexed by BSA, and the CG equation, using either ABW, AIBW or lean body weight (LBW) for the weight variable and compared with measured GFR, expressed in ml min(-1).

RESULTS

In our population of obese patients, use of the AIBW instead of the ABW in the CG equation, markedly improved the overall accuracy of this equation [57% for CGABW and 79% for CGAIBW (P < 0.05)]. For high BMI (over 40 kg m(-2)), the accuracy of the CG equations is no different when using LBW than when using AIBW. The MDRD and CKD-EPI equations de-indexed by the BSA also performed well, with an overall higher accuracy for the MDRD de-indexed equation [(80% and 76%, respectively (P < 0.05)].

CONCLUSIONS

The de-indexed MDRD equation appeared to be the most suitable for estimating the non-indexed GFR for the purpose of drug dosage adaptation in obese patients.

Glomerular filtration rate (GFR) during and after STEMI: a single-centre, methodological study comparing estimated and measured GFR

OBJECTIVES

To validate the performance of the most commonly used formulas for estimation of glomerular filtration rate (GFR) against measured GFR during the index hospitalisation for ST-elevation myocardial infarction (STEMI).

SETTING

Single centre, methodological study.

PARTICIPANTS

40 patients with percutaneous coronary intervention-treated STEMI were included between November 2011 and February 2013. Patients on dialysis, cardiogenic shock or known allergy to iodine were excluded.

OUTCOME MEASURES

Creatinine and cystatin C were determined at admission and before discharge in 40 patients with STEMI. Clearance of iohexol was measured (mGFR) before discharge. We evaluated and compared the Cockcroft-Gault (CG), the Modification of Diet in Renal Disease (MDRD-IDMS), the Chronic Kidney Disease Epidemiology (CKD-EPI) and the Grubb relative cystatin C (rG-CystC) with GFR regarding correlation, bias, precision and accuracy (P30). Agreement between eGFR and mGFR to discriminate CKD was assessed by Cohen's κ statistics.

RESULTS

MDRD-IDMS and CKD-EPI demonstrated good performance to estimate GFR (correlation 0.78 vs 0.81%, bias -1.3% vs 1.5%, precision 17.9 vs 17.1 mL/min 1.73 m(2) and P30 82.5% vs 82.5% for MDRD-IDMS vs CKD-EPI). CKD was best classified by CKD-EPI (κ 0.83). CG showed the worst performance (correlation 0.73%, bias -1% to 3%, precision 22.5 mL/min 1.73 m(2) and P30 75%). The rG-CystC formula had a marked bias of -17.8% and significantly underestimated mGFR (p=0.03). At arrival, CKD-EPI and rG-CystC had almost perfect agreement in CKD classification (κ=0.87), whereas at discharge agreement was substantially lower (κ=0.59) and showed a significant discrepancy in CKD classification (p=0.02). Median cystatin C concentration increased by 19%.

CONCLUSIONS

In acute STEMI, CKD-EPI showed the best CKD-classification ability followed by MDRD-IDMS, whereas CG performed the worst. STEMI altered the performance of the cystatin C equation during the acute phase, suggesting that other factors might be involved in the rise of cystatin C.

New standardized cystatin C and creatinine GFR equations in children validated with inulin clearance

BACKGROUND

This study compares glomerular filtration rate (GFR) equations in children based on standardized cystatin C (CYSC) and creatinine (CREA) and their combinations with renal clearance of inulin (C-inulin).

METHODS

A total of 220 children with different renal disorders were referred for C-inulin (median 84 ml/min/1.73 m(2)). Bias, precision (interquartile range, IQR), and accuracy (percentage of estimates ±30 % of C-inulin; P30) were evaluated for two cystatin C equations, CAPACYSC and BergCYSC, for creatinine equations, SchwartzCREA and GaoCREA, the arithmetic mean of CAPACYSC and SchwartzCREA (MEANCAPA+Schwartz), BergCYSC and SchwartzCREA (MEANBERG+SCHWARTZ) and the composite equation ChehadeCYSC+CREA.

RESULTS

Overall results of CAPACYSC, BergCYSC, SchwartzCREA, GaoCREA, MEANCAPA+Schwartz, MEANBERG+SCHWARTZ and ChehadeCYSC+CREA were: median bias -7.6/-4.9/-3.7/-2.3/-4.6/-4.0/-10.1 %, IQR 20.0/19.9/21.7/22.4/21.0/20.9/23.3 ml/min/1.73 m(2) and P30 86/86/80/83/89/91/83 %. The cystatin C equations, MEANCAPA+Schwartz and MEANBERG+SCHWARTZ had a more stable performance across subgroups compared with SchwartzCREA, GaoCREA and ChehadeCYSC+CREA.

CONCLUSIONS

Cystatin C was the preferred filtration marker for GFR estimation in children, while the benefit of combining cystatin C and creatinine deserves further investigations.

Accuracy of the estimation of glomerular filtration rate within a population of critically ill patients

BACKGROUND

Accuracy of glomerular filtration rate (GFR) estimates has been questioned and several authors recommend routine use of measured renal creatinine clearance (CLCR) as a surrogate of GFR in the intensive care unit (ICU). Our purpose was to compare estimates of GFR using Cockroft-Gault (CG), Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) and Modification of Diet in Renal Disease Study (MDRD) equations with 8h-CLCR, within a population of critically ill patients with a wide range of measured CLCR.

METHODS

Through a prospective, observational study of 54 patients with normal serum creatinine (sCr) admitted to ICU, daily 8h-CLCR (reference method) and GFR estimates (644 paired samples) were matched and compared. Augmented renal clearance (ARC) was defined as 8h-CLCR >130 ml/min/1.73 m(2).

RESULTS

No significant difference was found between mean 8h-CLCR (135.5 ml/min/1.73 m(2)) and CG equation (135.7 ml/min/1.73 m(2)), but significant differences (p < 0.01) were found for the MDRD (124.4 ml/min/1.73 m(2)) and CKD-EPI (107.6 ml/min/1.73 m(2)) equations. Correlation between 8h-CLCR and all estimates was weak (R = 0.2, 0.19 and 0.34, respectively). We observed poor agreement in terms of precision (40.9, 39.8 and 33.4%, respectively). Analysing subgroups, we observed that all equations significantly underestimated 8h-CLCR >120 ml/min/1.73 m(2) and overestimated 8h-CLCR <120 ml/min/1.73 m(2) (p < 0.05). The incidence of ARC patients was 55.6%.

CONCLUSIONS

Estimates of GFR using CG, CKD-EPI and MDRD formulae are flawed in the critically ill with normal sCr, significantly underestimating renal function in those with ARC and overestimating it in those with normal or decreased 8h-CLCR. Globally, the population exhibited ARC on more than half of the ICU admission days.

Evaluation of extended interval dosing aminoglycosides in the morbidly obese population

Aminoglycoside dosing has been studied in the obese population, typically recommending an adjusted weight utilizing a 40% dosing weight correction factor (IBW + 0.4 × (TBW-IBW)). These studies included limited numbers of morbidly obese patients and were not done in the era of extended interval aminoglycoside dosing. Here, we report a retrospective evaluation of morbidly obese patients receiving gentamicin or tobramycin at our hospital. The objective of this study was to evaluate the accuracy of the commonly recommended adjusted weight for weight-based dosing. There were 31 morbidly obese patients who received gentamicin or tobramycin 5-7 mg/kg every 24 hours using a 40% dosing weight correction factor. Our institution utilizes 16-hour postdose concentrations to monitor extended interval aminoglycosides. Twenty-two of the 31 patients (71%) achieved an appropriate serum drug concentration. Four patients (13%) were found to be supratherapeutic and 5 patients (16%) subtherapeutic. The only variable that correlated with supratherapeutic levels was older age (P = 0.0378). Our study helps to validate the current dosing weight correction factor (40%) in the morbidly obese population. We recommend caution when dosing aminoglycosides in morbidly obese patients who are of older age.

Functional range of creatinine clearance for renal drug dosing: a practical solution to the controversy of which weight to use in the Cockcroft-Gault equation

OBJECTIVE

To describe a practical solution for addressing body weight when using the Cockcroft-Gault equation to determine drug dosing.

DATA SOURCES

A literature search was conducted using PubMed MEDLINE (1980-April 2013) using creatinine clearance, Cockcroft and Gault, Cockcroft-Gault, body weight, and obesity as search terms. Reference citations from publications reviewed were included.

STUDY SELECTION AND DATA EXTRACTION

All English-language articles identified by the search were reviewed. Studies comparing the accuracy and bias of the Cockcroft-Gault equation using a variety of body weight designations in adult populations were included in the analysis.

DATA SYNTHESIS

Study results indicated that, for obese patients, ideal body weight (IBW) underestimates creatinine clearance (CrCl) and total body weight (TBW) overestimates CrCl. Some studies suggest that adjusted body weight with a factor of 0.4 is most accurate, while others suggest the use of lean body weight. These studies have failed to produce a definitive resolution to the controversy. Despite many well-designed studies, the Cockcroft-Gault body weight controversy remains unresolved and uncertainty continues to exist as to which form of weight should be used in the equation. A different perspective is warranted. Since renal dosing guidelines are generally based on ranges of CrCl, applying a CrCl range to describe a patient's renal function might be more practical than relying on a specific CrCl value. Ultimately, CrCl-based drug dosing involves the use of an imperfect mathematical approximation, which is then applied as precisely as possible to the benefit versus risk analysis for a specific patient.

CONCLUSIONS

We propose the use of a CrCl range for drug dosing purposes, with the lower boundary defined by using IBW in the Cockcroft-Gault equation and the upper boundary by using TBW.

Impact of renal function on treatment options and outcomes in advanced non-small cell lung cancer

INTRODUCTION

Certain chemotherapeutic agents commonly used for advanced non-small cell lung cancer (NSCLC) require minimum threshold renal function for administration. To determine how such requirements affect treatment options, we evaluated renal function patterns in this population.

METHODS

We performed a single-center retrospective analysis of patients treated for stage IV NSCLC from 2000 to 2007. Associations between patient characteristics, calculated creatinine clearance (CrCl), and clinical outcomes were determined using univariate and multivariate analyses, Cox proportional hazard models, and mixed model analysis.

RESULTS

298 patients (3930 creatinine measurements) were included in the analysis. Patients had a median of 5 (interquartile range [IQR] 4-18) Cr measurements. Median baseline CrCl was 96 mL/min (IQR 74-123 mL/min); median nadir CrCl was 78 mL/min (IQR 56-100mL/min). Renal function was associated with age (P<0.001), race (P=0.009), and gender (P=0.001). 23% of patients had a recorded CrCl<60 mL/min (threshold for cisplatin), with median onset 83 days after diagnosis and median time to recover to ≥60 mL/min of 27 (IQR 3-85) days; 11% of patients had a recorded CrCl<45 mL/min (threshold for pemetrexed), with median onset 122 days after diagnosis and median recovery time of 36 (IQR 3-73) days. For both thresholds, approximately 35% of patients had no documented recovery.

CONCLUSIONS

In this cohort of patients treated for stage IV NSCLC, renal function falls below commonly used thresholds for cisplatin and for pemetrexed in fewer than a quarter of patients. However, these declines may preclude administration of these drugs for prolonged periods.

Pharmacokinetics and monte carlo simulations of doripenem in patients with febrile neutropenia

BACKGROUND

Doripenem is a group 2 carbapenem with enhanced in vitro activity against gram-negative bacteria including Pseudomonas aeruginosa. There is a paucity of pharmacokinetic/pharmacodynamic data on doripenem in patients with febrile neutropenia.

OBJECTIVE

To conduct a pharmacokinetic evaluation of 2 doses of doripenem in patients with febrile neutropenia and provide probability estimates of attaining effective drug exposure against common gram-negative pathogens.

METHODS

We obtained multiple blood samples from 12 adults with febrile neutropenia who were receiving either 500 mg or 1000 mg of intravenous doripenem over 4 hours every 8 hours. Following at least 2 doses, serum concentrations were measured in each subject at 1, 4, 6, and 8 hours after initiation of a dose by a validated high-performance liquid chromatography assay. The derived pharmacokinetic parameters from these serum levels were used to perform a 5000-patient Monte Carlo simulation against bacteria with minimal inhibitory concentrations (MICs) of 0.008-64 mg/L to determine probability estimates of the time in which unbound drug concentrations remain above the MIC (fT(>MIC)).

RESULTS

The mean pharmacokinetic parameters in these patients were a volume of distribution of 43.9 L, an elimination rate constant of 0.37 h(-1), a total clearance of 14.4 L/h, and an area under the concentration-time curve of 57.6 mg•h/L. An optimal probability of target attainment (40% fT(>MIC)) of 90% was obtained against bacteria with MICs ≤2 mg/L and ≤4 mg/L with 500-mg and 1000-mg doses, respectively. Adverse events associated with doripenem were not observed.

CONCLUSIONS

The findings from this analysis of doripenem suggest that higher doses, as well as prolonged infusions, may be necessary to optimally treat selected gram-negative bacteria (eg, P. aeruginosa) in patients with febrile neutropenia.

Impact of various body weights and serum creatinine concentrations on the bias and accuracy of the Cockcroft-Gault equation

STUDY OBJECTIVE

To evaluate the impact of various body weights and serum creatinine (S(c) (r) ) concentrations on the bias and accuracy of the Cockcroft-Gault creatinine clearance (C-G Cl(c) (r) ) equation compared with measured 24-hour Cl(c) (r) .

DESIGN

Retrospective analysis.

SETTING

Tertiary care hospital.

PATIENTS

A total of 3678 patients with stable renal function and who underwent a 24-hour urine collection between July 1, 1996, and June 30, 2010.

MEASUREMENTS AND MAIN RESULTS

For each patient, C-G Cl(c) (r) was calculated and compared with a measured 24-hour Cl(c) (r) . Body weight adjustments to the calculation were performed based on the following weight classifications: underweight, normal weight, overweight, obese, and morbidly obese. In addition, C-G Cl(c) (r) was calculated by using rounded S(c) (r) values based on two S(c) (r) thresholds-0.8 mg/dl and 1 mg/dl-for patients with measured S(c) (r) values below those thresholds. Those patients were then evaluated after stratification into two age groups: all ages and a subgroup of patients aged 65 years or older. The S(c) (r) -rounded C-G Cl(c) (r) values were compared with the C-G Cl(c) (r) values using actual S(c) (r) values. Mean differences were calculated, and accuracy was evaluated. Use of actual body weight in the calculations for underweight patients resulted in an unbiased Cl(c) (r) of -0.22 ml/minute (p=0.898). Use of ideal body weight in the calculations of patients of normal weight returned an unbiased Cl(c) (r) of -1.3 ml/minute (p=0.544). An unbiased C-G Cl(c) (r) could not be calculated for other weight categories. In those patients, adjusted body weight using a factor of 0.4 (ABW(0.4) ) was the least biased and most accurate. In patients aged 65 years or older with an S(c) (r) less than 0.8 mg/dl and less than 1 mg/dl, actual S(c) (r) was unbiased (-3 ml/min [p=1] and -9 ml/min [p=0.279], respectively) and more accurate than rounded S(c) (r) . In patients of all ages with an S(c) (r) less than 0.8 mg/dl and less than 1 mg/dl, actual S(c) (r) proved less biased (-4.5 ml/min [p=0.038] and -5.5 ml/min [p<0.001], respectively) and more accurate than rounded S(c) (r) .

CONCLUSION

An unbiased C-G Cl(c) (r) can be calculated using actual body weight in underweight patients and ideal body weight in patients of normal weight. Using ABW(0.4) for overweight, obese, and morbidly obese patients appears to be the least biased and most accurate method for calculating their C-G Cl(c) (r) . Rounding S(c) (r) in patients with low S(c) (r) did not improve accuracy or bias of the Cl(cr) calculations.

Adjusting Eptifibatide Doses for Renal Impairment: A Model of Dosing Agreement Among Various Methods of Estimating Creatinine Clearance

Background:

Because of the renal elimination and increased risk for bleeding events at supratherapeutic doses of eptifibatide, the manufacturer recommends dosing adjustment in patients with renal dysfunction. Methods commonly used to estimate renal dysfunction in hospital settings may be inconsistent with those studied and recommended by the manufacturer

Objective:

To compare hypothetical renal dosing adjustments of eptifibatide using both the recommended method and several other commonly used formulas for estimating kidney function.

Methods:

Sex, age, weight, height, serum creatinine, and estimated glomerular filtration rate (eGFR) were obtained retrospectively from the records of patients who received eptifibatide during a 12-month period. Renal dosing decisions were determined for each patient based on creatinine clearance (CrCI) estimates via the Cockcroft-Gault formula (CG) with actual body weight (ABW), ideal body weight (IBW) or adjusted weight (ADJW), and eGFR from the Modification of Diet in Renal Disease formula. Percent agreement and Cohen κ were calculated comparing dosing decisions for each formula to the standard CG-ABW.

Results:

In this analysis of 179 patients, percent agreement as compared to CG-ABW varied (CG-IBW: 90.50%, CG-ADJW: 95.53%, and eGFR: 93.30%). All κ coefficients were categorized as good. In the 20% of patients receiving an adjusted dose by any of the methods, 68.6% could have received a dose different from that determined using the CG-ABW formula.

Conclusions:

In the patients with renal impairment (CrCI <50 mL/min) in this study, two thirds would have received an unnecessary 50% dose adjustment discordant from the manufacturer's recommendation. Because failure to adjust eptifibatide doses in patients with renal impairment has led to increased bleeding events, practitioners may be inclined to err on the side of caution. However, studies have shown that suboptimal doses of eptifibatide lead to suboptimal outcomes. Therefore, correct dosing of eptifibatide is important to both patient safety and efficacy.

Comparative evaluation of the Cockcroft-Gault Equation and the Modification of Diet in Renal Disease (MDRD) study equation for drug dosing: an opinion of the Nephrology Practice and Research Network of the American College of Clinical Pharmacy

Accurate assessment of kidney function is an important component of determining appropriate drug dosing regimens. Nearly all manufacturer-recommended dosage adjustments are based on creatinine clearance ranges derived from clinical pharmacokinetic studies performed during the drug development process. The Cockcroft-Gault (CG) equation provides an estimate of creatinine clearance and is the equation most commonly used to determine drug dosages in patients with impaired kidney function. The Modification of Diet in Renal Disease (MDRD) study equation has also been proposed for this purpose. Published studies report that drug dosages determined by the two equations do not agree in 10-40% of cases. However, interpretation and comparison of these studies are complicated by the variable creatinine methods used for calculating CG and MDRD estimates, the patient populations studied, and a lack of outcomes data demonstrating the clinical significance of dosing discrepancies. Moreover, the impact of reporting standardized serum creatinine values on the accuracy of the CG equation and corresponding drug dosing regimens have been questioned. Currently, no prospective pharmacokinetic studies have been conducted with use of the MDRD equation to generate dosing recommendations, and limited data are available to support its use in some patient populations representing demographic extremes. Collectively, these issues have resulted in considerable confusion among clinicians and have fueled a healthy debate on whether or not to use the MDRD equation to determine drug dosages. Each of these issues is reviewed, and a proposed algorithm for using creatinine-based kidney function assessments in drug dosing is provided. Knowledge of the advantages, limitations, and clinical role of each equation will facilitate their safe and effective use in drug dosing.

Validation of the Lund-Malmö, Chronic Kidney Disease Epidemiology (CKD-EPI) and Modification of Diet in Renal Disease (MDRD) equations to estimate glomerular filtration rate in a large Swedish clinical population

OBJECTIVE

The aim of this study was to validate externally the Swedish Lund-Malmö revised creatinine-based glomerular filtration rate (GFR) equations (LM Revised) in a Swedish cohort in comparison with the North American Modification of Diet in Renal Disease (MDRD) and Chronic Kidney Disease Epidemiology (CKD-EPI) equations.

MATERIAL AND METHODS

The study included 1397 examinations [median age 61 years, median body mass index (BMI) 26 kg/m(2)] in 996 patients referred for iohexol clearance (median 44 ml/min/1.73 m(2)). Bias, precision [interquartile range (IQR)], accuracy expressed as percentage of estimates ± 10% (P(10)) and ± 30% (P(30)) of measured GFR, and classification ability for five GFR stages (<15, 15-29, 30-59, 60-89 and ≥90 ml/min/1.73 m(2)) were compared.

RESULTS

Overall, all three equations performed satisfactorily: LM Revised, MDRD, CKD-EPI showed, respectively, a median bias of -5.8%, -2.2% and 1.7%, IQR 11.9, 12.3 and 11.7 ml/min/1.73 m(2), P(10) 35%, 34% and 38%, P(30) 84%, 79% and 79% and correctly classified GFR stages 68%, 65% and 69%. LM Revised was at least as accurate in terms of P(30) as the other equations at GFR intervals <90, while CKD-EPI was the only unbiased and the most accurate equation at ≥90 ml/min/1.73 m(2). LM Revised was more stable in terms of bias and accuracy across age and BMI groups than MDRD and CKD-EPI. Both MDRD and CKD-EPI overestimated measured GFR among elderly patients and in the small group of underweight men.

CONCLUSION

The ideal all-purpose GFR prediction equation does not exist. LM Revised should be preferred in patients with suspected or known renal insufficiency, while CKD-EPI is most useful in settings where patients with no a priori suspicion of renal impairment are evaluated. Differences in creatinine measurements between laboratories may limit the generalizability of the present validation.

Interpreting different measures of glomerular filtration rate in obesity and weight loss: pitfalls for the clinician

To combat the increasing incidence of obesity, much research has been devoted to devising successful strategies for weight loss, including manipulation of diet and gastric surgery. Obesity itself can be associated with renal dysfunction, and the degree of reversibility of this with weight loss has being studied. However, there are significant limitations and flaws in the methods we have available to measure glomerular filtration rate (GFR) in overweight and obese subjects. Obesity is associated with changes in body composition including lean and fat mass. This has implications for assumptions that underpin creatinine-based measures such as creatinine clearance, estimated GFR and other equations devised for obesity including the Salazar-Corcoran equation. These changes in body composition also affect measures of glomerular filtration such as cystatin C and nuclear medicine isotope scans. This article will review the accuracy of these current measures of renal function in the obese and consider the evidence for adjusting for body surface area or adjusting for lean body mass. Finally, the effect of weight loss itself on serial measurements of renal function in a given individual, independent of a true change in renal function, will be reviewed. Ultimately using the Cockcroft-Gault equation with an adjustment for lean body mass seems to be the best measure for renal function in obesity. No method for measuring renal function in situations of weight loss has been shown to be unequivocally superior.

Predictive performance of 12 equations for estimating glomerular filtration rate in severely obese patients

ABSTRACT Objective: Considering that the Cockcroft-Gault formula and the equation of diet modification in renal disease are amply used in clinical practice to estimate the glomerular filtration rate, although they seem to have low accuracy in obese patients, the present study intends to evaluate the predictive performance of 12 equations used to estimate the glomerular filtration rate in obese patients. Methods: This is a cross-sectional retrospective study, conducted between 2007 and 2008 and carried out at a university, of 140 patients with severe obesity (mean body mass index 44 ± 4.4 kg/m2). The glomerular filtration rate was determined by means of 24-hour urine samples. Patients were classified into one or more of the four subgroups: impaired glucose tolerance (n = 43), diabetic (n = 24), metabolic syndrome (n = 76), and/or hypertension (n = 66). We used bias, precision, and accuracy to assess the predictive performance of each equation in the entire group and in the subgroups. Results: In renal disease, Cockcroft-Gault's formula and the diet modification equation are not precise in severely obese patients (precision: 40.9 and 33.4, respectively). Sobh's equation showed no bias in the general group or in two subgroups. Salazar-Corcoran's and Sobh's equations showed no bias for the entire group (Bias: −5.2, 95% confidence interval (CI) = −11.4, 1.0, and 6. 2; 95%CI = −0.3, 12.7, respectively). All the other equations were imprecise for the entire group. Conclusion: Of the equations studied, those of Sobh and Salazar-Corcoran seem to be the best for estimating the glomerular filtration rate in severely obese patients analyzed in our study.

Use of Recalibrated Serum Creatinine Concentrations for Adjustment of Drug Dosages: Determination of Values Compatible with Conventional Dosing Recommendations

BACKGROUND:

Measurement of serum creatinine concentration is central to evaluation of kidney function. Recent efforts to increase the accuracy of this evaluation have led to recalibration of laboratory instruments. Recalibrated creatinine concentrations often are lower than previously reported.

OBJECTIVES:

To derive a method for converting recalibrated serum creatinine (R-SCr) concentrations into values that are compatible with recommended equations for calculation of estimated creatinine clearance.

METHODS:

Beginning with a proprietary array of recalibrated and corresponding non-recalibrated serum creatinine (NR-SCr) numerical data provided by the instrument manufacturer, relationships were examined with exponential and linear regression analyses. The validity of derived values for NR-SCr obtained through these analyses was tested by comparison of proprietary and derived serum creatinine concentrations and calculated creatinine clearance values.

RESULTS:

Analyses revealed that relationships between R-SCr and NR-SCr creatinine were essentially linear. Rearranging and solving the equation for a straight line described this relationship as x = (y - b)/m, where x is the derived creatinine value, y is the R-SCr concentration, and, for our laboratory instrument, best parameters for m and b equal to 0.987 and −0.07, respectively. Use of these parameters to derive NR-SCr values was shown to significantly decrease positive bias in subsequent creatinine clearance calculations.

CONCLUSIONS:

As compared to R-SCr concentrations, use of derived NR-SCr values can improve the predictive performance of conventional equations used to calculate estimated creatinine clearance.

Pharmacokinetics of intravenous levofloxacin administered at 750 milligrams in obese adults

The physiochemical properties of levofloxacin suggest that it is an agent which may exhibit altered pharmacokinetics in obese individuals. The purpose of this study was to describe the pharmacokinetics of a single 750-mg intravenous dose of levofloxacin in both hospitalized and ambulatory obese individuals. The hypothesis was that a standard dose of levofloxacin in obese individuals would achieve serum concentrations likely to be therapeutic. A single levofloxacin dose of 750 mg was infused over 90 min, and seven serial serum samples were subsequently obtained to evaluate the pharmacokinetics after the first dose. The peak concentrations of levofloxacin were comparable to those seen with normal-weight individuals. However, the area under the concentration-time curve and clearance were quite variable. Accelerated clearance was evident in the ambulatory obese individuals. Further investigation of the effects of obesity on the pharmacokinetics of levofloxacin is necessary to ensure optimal dosing.

Postoperative renal function in patients is unaltered after robotic-assisted radical prostatectomy

Background

Pneumoperitoneum with an intra-abdominal pressure (IAP) of 14 mmHg is known to decrease renal function. Robotic-assisted radical prostatectomy (RARP) requires an IAP of more than 15 mmHg for operation. Therefore, we retrospectively investigated whether patients who underwent RARP experienced renal insufficiency during the postoperative period (at postoperative days 7 and 30).

Methods

One hundred patients who underwent RARP were enrolled in this study. Preoperative serum blood urea nitrogen (BUN) and serum creatinine (Cr) levels were measured. Creatinine clearance (CrCl) was calculated using the Cockcroft and Gault formula. CrCl was calculated at 1 day before surgery (baseline), 2 hr postoperatively, and at 1, 3, 7, and 30 days postoperatively (POD 1, POD 3, POP 7, and POD 30). Patients were assigned to abnormal CrCl (n = 52) or normal CrCl groups (n = 48) on the basis of these measurements.

Results

Significant inter-group differences in BUN, Cr, and CrCl were observed at all postoperative time points. BUN and Cr decreased significantly at postoperative 2 hr and POD 1, 3, and 7 versus baseline in both groups, whereas CrCl increased significantly at postoperative 2 hr and POD 1, 3, and 7 versus baseline in both groups. However, BUN, Cr, and CrCl were similar at POD 30 and preoperatively in the two groups.

Conclusions

RAPR, which requires an IAP of 15-20 mmHg for more than 4 hr, does not induce renal dysfunction during the postoperative period, and even in those patients with an abnormal CrCl.

Measurement of glomerular filtration rate in obese patients: pitfalls and potential consequences on drug therapy

Epidemiological studies have shown that obesity is associated with chronic kidney disease and end stage renal disease. These studies have used creatinine derived equations to estimate glomerular filtration rate (GFR) and have indexed GFR to body surface area (BSA). However, the use of equations using creatinine as a surrogate marker of glomerular filtration and the indexation of GFR for BSA can be questioned in the obese population. First, these equations lack precision when they are compared to gold standard GFR measurements such as inulin clearances; secondly, the indexation of GFR for 1.73 m(2) of BSA leads to a systematic underestimation of GFR compared to absolute GFR in obese patients who have BSA that usually exceed 1.73 m(2). Obesity is also associated with pathophysiological changes that can affect the pharmacokinetics of drugs. The effect of obesity on both renal function and drug pharmacokinetics raises the issue of correct drug dosage in obese individuals. This may be particularly relevant for drugs known to have a narrow therapeutic range or excreted by the kidney.

Methods to evaluate renal function in elderly patients: a systematic literature review

CONTEXT

multiple studies of elderly patients show that the prevalence of chronic renal failure in people aged 65 years and older is dependent on the method used to calculate the glomerular filtration rate. We performed a systematic literature search with research question: What is the best method that could be applicable in clinical practice for evaluating renal function in the elderly? Studies using inulin, Cr-51-EDTA, Tc-DTPA or iohexol assays as the gold standard were included.

METHODS

we searched the PubMed and EMBASE databases. Articles found were screened first by title and abstract and then by five criteria. Retained articles were scored using an adapted version of QUADAS.

RESULTS

twelve articles had an identified population or subpopulation aged 65 years and older. The studies were heterogeneous with regard to the population investigated and the statistical procedures used to compare the methods and equations with the gold standard. The Cockcroft-Gault (CG) and MDRD equations and the serum cystatin C concentration produced the highest correlations with the gold standard.

CONCLUSIONS

no accurate method to evaluate renal function in the elderly was found. Serum cystatin C concentration and the CG and MDRD formula might be valuable parameters, although there is insufficient evidence.

Standardization of p‐creatinine assays and use of lean body mass allow improved prediction of calculated glomerular filtration rate in adults: A new equation

OBJECTIVE

To evaluate the Cockcroft-Gault (CG) equation, using various body weight expressions, and the Sawyer equation in predicting glomerular filtration rate (GFR) using an enzymatic and zero-calibrated Jaffe plasma-creatinine assay, and to derive a new robust equation in adults.

MATERIAL AND METHODS

The CG weight measures included total, ideal and adjusted body weight (ABW; lowest of total and ideal) and two lean body mass (LBM) expressions, while the Sawyer equation is based primarily on LBM. Iohexol clearance was used to measure GFR. One derivation set (n = 436; enzymatic assay) was used to evaluate and bias-adjust existing equations when indicated, and to derive a new equation based on plasma-creatinine, age, gender and the body weight measure yielding the best adjusted R2. All equations were then validated in a separate set (n = 414; Jaffe assay).

RESULTS

The existing equations all performed similarly in both sets. Prediction errors of equations based on LBM showed no correlation with BMI. The CGABW and Sawyer equations performed best. The new equation with LBM yielded the highest adjusted R2. In the combined set (n = 850), its accuracy (86 %/98 % of estimates within 30 %/50 % of measured GFR) was significantly better than for the CGABW (79 %/95 %) and Sawyer equations (79 %/93 %) (p<0.001) for each 30 mL/min GFR subgroup within +/-30 % and +/-50 %, except within +/-30 % >120 mL/min. Prediction error did not correlate with BMI, age or gender.

CONCLUSION

A new creatinine-based equation derived in a mainly Caucasian patient sample is a better predictor of GFR than CG-type equations irrespective of the body weight measure used or, if bias-adjusted, when using zero-calibrated creatinine assays.

Comparison of drug dosing recommendations based on measured GFR and kidney function estimating equations

BACKGROUND

Kidney disease alters the pharmacokinetic disposition of many medications, requiring dosage adjustment to maintain therapeutic serum concentrations. The Cockcroft-Gault (CG) equation is used for pharmacokinetic studies and drug dosage adjustments, but the Modification of Diet in Renal Disease (MDRD) Study equation is more accurate and more often reported by clinical laboratories than the CG equation.

STUDY DESIGN

Diagnostic test study.

SETTINGS & PARTICIPANTS

Pooled data set for 5,504 participants from 6 research studies and 4 clinical populations with measured glomerular filtration rate (GFR).

INDEX TEST

Estimated kidney function using the MDRD Study and CG equations incorporating actual (CG) or ideal body weight (CG(IBW)) and standardized serum creatinine concentrations.

REFERENCE TEST

Measured GFR assessed by using iodine-125-iothalamate urinary clearance.

OUTCOME

Concordance of assigned kidney function categories designated by the Food and Drug Administration (FDA) Guidance for Industry for pharmacokinetic studies and recommended dosages of 15 medications cleared by the kidneys.

RESULTS

Concordance of kidney function estimates with measured GFR for FDA-assigned kidney function categories was 78% for the MDRD Study equation compared with 73% for the CG equation (P < 0.001) and 66% for the CG(IBW) equation (P < 0.001). Concordance between the MDRD Study equation and CG and CG(IBW) equations was 78% and 75%, respectively (P < 0.001). Concordance of kidney function estimates with measured GFR for recommended drug dosages was 88% for MDRD Study equation compared with 85% for the CG equation (P < 0.001) and 82% for the CG(IBW) equation (P < 0.001), with lower concordance when dosing recommendations for drugs included narrow GFR ranges. Concordance rates between the CG and CG(IBW) equations and MDRD Study equation were 89% and 88%, respectively (P < 0.05).

LIMITATIONS

Results based on simulation rather than pharmacokinetic studies. Outcome was drug dosage recommendations, rather than observed drug efficacy and safety.

CONCLUSIONS

The MDRD Study equation can also be used for pharmacokinetic studies and drug dosage adjustments. As more accurate GFR-estimating equations are developed, they should be used for these purposes.

Validation of a new plasma cystatin C-based formula and the Modification of Diet in Renal Disease creatinine-based formula for determination of glomerular filtration rate

OBJECTIVE

New proposed definitions of chronic kidney disease necessitate the development and use of simple and accurate methods for estimating glomerular filtration rate (GFR). Plasma cystatin C has been shown to be a more reliable GFR marker than creatinine and formulae for estimating GFR have been reported. The purpose of this study was to validate a cystatin C-based GFR prediction equation in a different population from the derivation set but using the cystatin C assay of a single laboratory, and to compare the results with that of the creatinine-based Modification of Diet in Renal Disease (MDRD) Study equation.

MATERIAL AND METHODS

A newly presented formula based on plasma cystatin C and gender and the MDRD formula based on creatinine for estimation of GFR were validated in an unselective patient material. Single sample iohexol clearance was used as the GFR reference method in 406 consecutive patients with GFR varying from normal to poor renal function. The creatinine assay used was standardized to express true plasma creatinine.

RESULTS

Median bias (1.1%) and accuracy (79.1% of the estimates within +/-30% of iohexol clearance) of the cystatin C formula were close to the derivation set. The accuracy was significantly higher than that of the original four-variable MDRD equation (73.2%; median bias 9.8%). However, the accuracy did not differ significantly from that of the re-expressed MDRD formula (79.6%; median bias 3.2%) based on true creatinine. Both formulae performed with a low bias and acceptable accuracy up to a GFR of 90 ml/min/1.73 m(2).

CONCLUSIONS

GFR estimation based on plasma cystatin C performed equally well in the validation as in the derivation set, and was as accurate as the re-expressed MDRD creatinine-based equation.

Estimation of creatinine clearance in morbidly obese patients

PURPOSE

Estimates of creatinine clearance (CL(cr)) based on equations and various body-size descriptors were compared with 24-hour measured CL(cr) values in morbidly obese patients.

METHODS

Patients age 18-75 years with a body mass index (BMI) of >/=40 kg/m(2) with stable serum creatinine values were enrolled. Covariates known to contribute to alteration in CL(cr) were used to exclude patients. Twenty-four-hour urine collection was performed to measure CL(cr). Bioelectric impedance analysis was used to estimate fat-free weight (FFW). Glomerular filtration rate was estimated using the four-variable Modification of Diet in Renal Disease (MDRD4) equation. CL(cr) was estimated using the Cockcroft-Gault and Salazar-Corcoran methods using total body weight (TBW). Body-size descriptors, such as ideal body weight (IBW), adjusted body weight (ABW), and lean body weight (LBW), and FFW were substituted in the Cockcroft-Gault equation to generate additional estimates of CL(cr).

RESULTS

Fifty-four patients (mean +/- S.D. age, 48.4 +/- 12.9 years; TBW, 142.3 +/- 41.7 kg; BMI, 50.5 +/- 12.6 kg/m(2)) completed the study. All three equations were biased in their estimation of CL(cr). Use of MDRD4 and IBW in the Cockcroft-Gault equation underestimated CL(cr), while the Salazar-Corcoran equation and use of TBW or ABW in the Cockcroft-Gault equation overestimated this value. Substitution of fat-free weight or LBW in the Cockcroft-Gault equation provided unbiased estimates of CL(cr).

CONCLUSION

An LBW estimate, based on TBW and BMI, incorporated into the Cockcroft-Gault equation provided an unbiased, relatively precise, accurate, and clinically practical estimate of 24-hour measured CL(cr) in morbidly obese patients.

Comparison of drug dosing recommendations based on measured GFR and kidney function estimating equations

BACKGROUND

Kidney disease alters the pharmacokinetic disposition of many medications, requiring dosage adjustment to maintain therapeutic serum concentrations. The Cockcroft-Gault (CG) equation is used for pharmacokinetic studies and drug dosage adjustments, but the Modification of Diet in Renal Disease (MDRD) Study equation is more accurate and more often reported by clinical laboratories than the CG equation.

STUDY DESIGN

Diagnostic test study.

SETTINGS & PARTICIPANTS

Pooled data set for 5,504 participants from 6 research studies and 4 clinical populations with measured glomerular filtration rate (GFR).

INDEX TEST

Estimated kidney function using the MDRD Study and CG equations incorporating actual (CG) or ideal body weight (CG(IBW)) and standardized serum creatinine concentrations.

REFERENCE TEST

Measured GFR assessed by using iodine-125-iothalamate urinary clearance.

OUTCOME

Concordance of assigned kidney function categories designated by the Food and Drug Administration (FDA) Guidance for Industry for pharmacokinetic studies and recommended dosages of 15 medications cleared by the kidneys.

RESULTS

Concordance of kidney function estimates with measured GFR for FDA-assigned kidney function categories was 78% for the MDRD Study equation compared with 73% for the CG equation (P < 0.001) and 66% for the CG(IBW) equation (P < 0.001). Concordance between the MDRD Study equation and CG and CG(IBW) equations was 78% and 75%, respectively (P < 0.001). Concordance of kidney function estimates with measured GFR for recommended drug dosages was 88% for MDRD Study equation compared with 85% for the CG equation (P < 0.001) and 82% for the CG(IBW) equation (P < 0.001), with lower concordance when dosing recommendations for drugs included narrow GFR ranges. Concordance rates between the CG and CG(IBW) equations and MDRD Study equation were 89% and 88%, respectively (P < 0.05).

LIMITATIONS

Results based on simulation rather than pharmacokinetic studies. Outcome was drug dosage recommendations, rather than observed drug efficacy and safety.

CONCLUSIONS

The MDRD Study equation can also be used for pharmacokinetic studies and drug dosage adjustments. As more accurate GFR-estimating equations are developed, they should be used for these purposes.

The Lund-Malmö creatinine-based glomerular filtration rate prediction equation for adults also performs well in children

OBJECTIVE

To evaluate the clinical performance in a paediatric population of the Lund-Malmö creatinine-based glomerular filtration rate (GFR) prediction equations, primarily developed for adults.

MATERIAL AND METHOD

Iohexol clearance was used as the gold standard in 85 paediatric Caucasian patients (0.3-17 years; 37 F/48 M). One Lund-Malmö equation was based on age and gender (LM) and one included lean body mass (LM-LBM). Comparisons focused on correlation (adjusted R2), bias (median percent error) and accuracy (proportions of predicted GFR differing < or = 30% from measured GFR) (mL/min/1.73 m2). The performances were compared with those of the Modification of Diet in Renal Disease (MDRD) Study equation, a dedicated paediatric creatinine equation, Counahan-Barratt (CB) and a cystatin C-based equation.

RESULTS

The MDRD equation performed poorly with a median bias of 96%. Of the remaining equations, only the LM-LBM produced significant bias (+10% in median) according to line of identity regression analysis. The LM equation yielded marginally higher accuracy (76%) than the LM-LBM equation (74%) and the CB (73%), but lower than the cystatin C-based equation (82%). However, the estimated accuracy figures for these four equations were generally imprecise and none of the differences compared with the LM equation was statistically significant.

CONCLUSION

In contrast to most creatinine-based GFR prediction equations, the LM equation performs adequately for both children and adults. This may be due to the unique model-building principles used when the LM equation was established. Further validation in a larger paediatric population is necessary.

Effect of Preoperative Renal Dysfunction on Mortality and Postoperative Renal Failure Following Endovascular Abdominal Aortic Aneurysm Repair

This study was aimed to assess the effect of preoperative renal dysfunction on mortality and postoperative renal failure in patients undergoing elective endovascular repair of abdominal aortic aneurysm. A total of 155 patients with a mean age of 74.9 years (±6.4) were included. In all, 31 patients (20%) had a preoperative creatinine level of >1.5 mg/dL, whereas 66 patients (42.6%) had an estimated glomerular filtration rate of <60 mL/min. Perioperative mortality was 2.6% with no significant difference between those with and without abnormal renal indices. Long-term survival at 4 years was 30% in patients with creatinine >1.5 mg/dL compared to over 60% in those with normal creatinine ( P < .02). The difference in long-term survival was not as significant in patients with normal or reduced glomerular filtration rate ( P = .13). However, neither creatinine nor glomerular filtration rate were found to accurately predict survival even though both demonstrated strong predictivity for postoperative renal failure in patients undergoing elective endovascular repair of abdominal aortic aneurysm.

Efficacy and safety of atrasentan in patients with cardiovascular risk and early atherosclerosis

Endothelin plays an important role in the pathogenesis of atherosclerosis. The aim of the study was to evaluate the safety and hemodynamic and metabolic responses to 6 months treatment with atrasentan, the selective endothelin-A receptor antagonist. Seventy-two patients with multiple cardiovascular risk factors and nonobstructive coronary artery disease on coronary angiogram were randomly assigned in a double-blind manner to atrasentan or placebo. Mean aortic blood pressure decreased from 92+/-10 to 80+/-10 mm Hg (P<0.001) in the atrasentan group and did not change in the placebo group (93+/-10 and 92+/-11 mm Hg; P=0.84). The difference between the groups was significant (P<0.001). No effect on heart rate was observed. In a subgroup of patients not treated with angiotensin-converting enzyme inhibitor, creatinine level decreased in the atrasentan versus the placebo group (P=0.011). Fasting glucose (P=0.026), glycosylated hemoglobin level (P=0.041), triglyceride l (P=0.013), lipoprotein-A (P=0.046), and uric acid levels (P=0.048) decreased significantly in the atrasentan group compared with the placebo group. No progression of angiographic coronary disease was observed. The most common adverse effects with atrasentan were nasal stuffiness, headache, and edema. In conclusion, 6 months of treatment with atrasentan results in a reduction of blood pressure and improvement in glucose and lipid metabolism. These findings suggest the beneficial role of atrasentan in the treatment of hypertension and metabolic syndrome.

Prediction of relative glomerular filtration rate in adults: new improved equations based on Swedish Caucasians and standardized plasma-creatinine assays

OBJECTIVE

To evaluate newly developed equations predicting relative glomerular filtration rate(GFR) in adult Swedish Caucasians and to compare with the Modification of Diet in Renal Disease(MDRD) and Mayo Clinic equations using enzymatic and zero-calibrated plasma creatinine assays.

MATERIAL AND METHODS

GFR was measured with iohexol clearance adjusted to 1.73 m(2). One population sample (n=436/Lund) was used to derive an equation based on plasma-creatinine/age/gender, and a second with the addition of lean body mass (LBM). Both equations were validated in a separate sample (n=414/Malmö). The coefficients of the equations were eventually fine-tuned using all 850 patients and yielding Lund-Malmö equations without (LM) and with LBM-term (LM(LBM)). Their performance was compared with the MDRD(CC) (conventional creatinine calibration), MDRD(IDMS) (isotope dilution mass spectroscopy traceable calibration) and Mayo Clinic equations.

RESULTS

The Lund equations performed similarly in both samples. In the combined set, the Mayo Clinic/MDRD(CC) resulted in +19.0/+10.2 % median bias, while bias for the other equations was < 10 %. LM(LBM) had the highest accuracy (86 % of estimates within 30 % of measured GFR), significantly (p < 0.001) better than for MDRD(IDMS) (80 %). In men with BMI < 20 kg/m(2), MDRD(IDMS)/LM had +46 %/+19 % median bias. MDRD(IDMS) also overestimated GFR by 22 %/14 % in men/women above 80 years of age. The LM(LBM) equation had < 10 % bias irrespective of BMI, age or GFR except for a 15 % negative bias at GFR > 90 mL/min/1.73 m(2).

CONCLUSION

The newly developed Lund-Malmö equations for GFR estimation performed better than the MDRD(IDMS) and Mayo Clinic equations in a Swedish Caucasian sample. Inclusion of an LBM term improved performance markedly in certain subgroups.