Thomas C. Dowling

Nesiritide does not improve renal function in patients with chronic heart failure and worsening serum creatinine

Background—Nesiritide (synthetic human brain natriuretic peptide) is approved for the treatment of symptomatic heart failure. However, studies of brain natriuretic peptide in patients with heart failure have come to conflicting conclusions about effects on glomerular filtration rate (GFR), effective renal plasma flow, natriuresis, and diuresis. Methods and Results—To identify a population at high risk of renal dysfunction with conventional treatment, we selected patients with a creatinine level increased from baseline (within 6 months). We examined the effects of nesiritide on GFR (measured by iothalamate clearance), renal plasma flow (measured by para-amino hippurate clearance), urinary sodium excretion, and urine output in a double-blind, placebo-controlled, crossover study. Patients received nesiritide (2 &mgr;g/kg IV bolus followed by an infusion of 0.01 &mgr;g/kg per minute) or placebo for 24 hours on consecutive days. Nesiritide and placebo data were compared by repeated-measures analysis and Student t test. We studied 15 patients with a recent mean baseline creatinine of 1.5±0.4 mg/dL and serum creatinine of 1.8±0.8 mg/dL on admission to the study. There were no differences in GFR, effective renal plasma flow, urine output, or sodium excretion for any time interval or for the entire 24-hour period between the nesiritide and placebo study days. For 24 hours, urine output was 113±51 mL/h with placebo and 110±56 mL/h with nesiritide. GFR during placebo was 40.9±25.9 mL/min and with nesiritide was 40.9±25.8. Conclusions—Nesiritide did not improve renal function in patients with decompensated heart failure, mild chronic renal insufficiency, and renal function that had worsened compared with baseline. The lack of effect may be related to renal insufficiency, hemodynamic alterations, sodium balance, severity of heart failure, or drug dose. Understanding the importance of these issues will permit effective and appropriate use of nesiritide.

A Randomized, Controlled Trial of the Renal Effects of Ultrafiltration as Compared to Furosemide in Patients With Acute Decompensated Heart Failure

OBJECTIVES This study was designed to evaluate the consequences of ultrafiltration (UF) and standard intravenous diuretic (furosemide) therapy on glomerular filtration rate (GFR) and renal plasma flow in patients with acute decompensated heart failure. BACKGROUND It has been hypothesized that treatment with diuretics may worsen renal function as the result of systemic neurohormonal activation and direct renal vascular effects. UF also removes fluid, but its actions on intrarenal hemodynamics, and therefore renal function, are unknown. METHODS Patients hospitalized for acute decompensated heart failure with an ejection fraction less than 40% and two or more signs of hypervolemia were randomized to receive UF or intravenous diuretics. Urine output, GFR (as measured by iothalamate), and renal plasma flow (as measured by para-aminohippurate) were assessed before fluid removal and after 48 hours. RESULTS Nineteen patients (59 +/- 16 years, 68% were male) were randomized to receive UF (n = 9) or intravenous diuretics (n = 10). The change in GFR (-3.4 +/- 7.7 mL/min vs. -3.6 +/- 11.5 mL/min; P = .966), renal plasma flow (26.6 +/- 62.7 mL/min vs. 16.1 +/- 42.0 mL/min; P = .669), and filtration fraction (-6.9 +/- 13.6 mL/min vs. -3.9 +/- 13.6 mL/min; P = .644) after treatment were not significantly different between the UF and furosemide treatment groups, respectively. There was no significant difference in net 48-hour fluid removal between the groups (-3211 +/- 2345 mL for UF and -2725 +/- 2330 mL for furosemide, P = .682). UF removed 3666 +/- 2402 mL. Urine output during 48 hours was significantly greater in the furosemide group (5786 +/- 2587 mL) compared with the UF group (2286 +/- 915 mL, P < .001). CONCLUSIONS During a 48-hour period, UF did not cause any significant differences in renal hemodynamics compared with the standard treatment of intravenous diuretics.

Characterization of hepatic cytochrome P4503A activity in patients with end‐stage renal disease

The cytochrome P450 (CYP) oxidative enzyme system, located primarily in the liver and small intestine, is responsible for metabolism and detoxification of numerous endogenous and exogenous substances. The most abundant CYP enzyme, CYP3A, is known to be involved in the metabolism of more than 200 commonly used medications. In experimental models of renal failure, both hepatic function and CYP enzyme content are reduced; however, direct evidence in humans is lacking. Evaluation of drug metabolism in patients with end‐stage renal disease is important because these patients use a large number of medications and are at risk of adverse reactions and drug‐drug interactions.

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 1 0–40% 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.

Performance of chronic kidney disease epidemiology collaboration creatinine‐cystatin C equation for estimating kidney function in cirrhosis

Conventional creatinine‐based glomerular filtration rate (GFR) equations are insufficiently accurate for estimating GFR in cirrhosis. The Chronic Kidney Disease Epidemiology Collaboration (CKD‐EPI) recently proposed an equation to estimate GFR in subjects without cirrhosis using both serum creatinine and cystatin C levels. Performance of the new CKD‐EPI creatinine‐cystatin C equation (2012) was superior to previous creatinine‐ or cystatin C‐based GFR equations. To evaluate the performance of the CKD‐EPI creatinine‐cystatin C equation in subjects with cirrhosis, we compared it to GFR measured by nonradiolabeled iothalamate plasma clearance (mGFR) in 72 subjects with cirrhosis. We compared the “bias,” “precision,” and “accuracy” of the new CKD‐EPI creatinine‐cystatin C equation to that of 24‐hour urinary creatinine clearance (CrCl), Cockcroft‐Gault (CG), and previously reported creatinine‐ and/or cystatin C‐based GFR‐estimating equations. Accuracy of CKD‐EPI creatinine‐cystatin C equation as quantified by root mean squared error of difference scores (differences between mGFR and estimated GFR [eGFR] or between mGFR and CrCl, or between mGFR and CG equation for each subject) (RMSE = 23.56) was significantly better than that of CrCl (37.69, P = 0.001), CG (RMSE = 36.12, P = 0.002), and GFR‐estimating equations based on cystatin C only. Its accuracy as quantified by percentage of eGFRs that differed by greater than 30% with respect to mGFR was significantly better compared to CrCl (P = 0.024), CG (P = 0.0001), 4‐variable MDRD (P = 0.027), and CKD‐EPI creatinine 2009 (P = 0.012) equations. However, for 23.61% of the subjects, GFR estimated by CKD‐EPI creatinine‐cystatin C equation differed from the mGFR by more than 30%. Conclusion: The diagnostic performance of CKD‐EPI creatinine‐cystatin C equation (2012) in patients with cirrhosis was superior to conventional equations in clinical practice for estimating GFR. However, its diagnostic performance was substantially worse than reported in subjects without cirrhosis. (Hepatology 2014;59:1532‐1542)

Evaluation of Renal Drug Dosing: Prescribing Information and Clinical Pharmacist Approaches

Study Objective. To characterize renal function parameters reported in United States Food and Drug Administration‐approved prescribing information (package inserts), to compare dosage recommendations for patients with impaired renal function between prescribing information and tertiary drug dosing references, and to evaluate renal function quantification methods most commonly used by clinical pharmacists to develop dosage regimens.

Peginterferon Pharmacokinetics in African American and Caucasian American Patients with Hepatitis C Virus Genotype 1 Infection

BACKGROUND & AIMS The relationship between serum peginterferon pharmacokinetics and pharmacodynamics and the early virologic response (EVR) to peginterferon and ribavirin therapy was assessed in patients with chronic hepatitis C virus (HCV) genotype 1 infection. METHODS A total of 333 patients (160 African Americans [AA] and 173 Caucasian Americans [CA]) who received peginterferon alpha-2a (180 microg/wk) without a dose modification during the initial 4 weeks of therapy were analyzed. Peginterferon and 2,5-oligoadenylate synthetase (2,5-OAS) serum levels were measured on days 0, 1, 2, 3, 7, 14, 28, 56, 84, and 168 of treatment. The EVR (>or=2-log(10) decline in HCV RNA levels by week 12 of therapy) was the primary virologic end point. RESULTS Peginterferon pharmacokinetics after the first dose were similar in AA and CA, but AA had greater peginterferon concentrations at days 1, 3, 14, and 28 (P < .05). AA had higher absolute serum 2,5-OAS levels on days 0, 1, 2, 3, 7, 14, 28, and 56 (P < .05), but the magnitude of 2,5-OAS induction during treatment were similar. AA patients showed a smaller decline in serum HCV RNA during the first 28 days of treatment (P < .001) and a lower EVR (65% vs 83%). AA and CA with EVR had significantly higher serum peginterferon concentrations and serum 2,5-OAS induction during the first 12 weeks than patients without an EVR. CONCLUSIONS Peginterferon alpha-2a pharmacokinetic and pharmacodynamic variability is associated with EVR in both AA and CA with HCV infection, but do not explain the racial disparity in combination treatment efficacy.

Renal Interaction Between Itraconazole and Cimetidine

Renal drug interactions can result from competitive inhibition between drugs that undergo extensive renal tubular secretion by transporters such as P‐glycoprotein (P‐gp). The purpose of this study was to evaluate the effect of itraconazole, a known P‐gp inhibitor, on the renal tubular secretion of cimetidine in healthy volunteers who received intravenous cimetidine alone and following 3 days of oral itraconazole (400 mg/day) administration. Glomerular filtration rate (GFR) was measured continuously during each study visit using iothalamate clearance. Iothalamate, cimetidine, and itraconazole concentrations in plasma and urine were determined using high‐performance liquid chromatography/ultraviolet (HPLC/UV) methods. Renal tubular secretion (CLsec) of cimetidine was calculated as the difference between renal clearance (CLr) and GFR (CLioth) on days 1 and 5. Cimetidine pharmacokinetic estimates were obtained for total clearance (CLT), volume of distribution (Vd), elimination rate constant (Kel), area under the plasma concentration‐time curve (AUC0–240 min), and average plasma concentration (Cpave) before and after itraconazole administration. Plasma itraconazole concentrations following oral dosing ranged from 0.41 to 0.92 μg/mL. The cimetidine AUC0–240 min increased by 25% (p < 0.01) following itraconazole administration. The GFR and Vd remained unchanged, but significant reductions in CLT (655 vs. 486 mL/min, p < 0.001) and CLsec (410 vs. 311 mL/min, p = 0.001) were observed. The increased systemic exposure of cimetidine during coadministration with itraconazole was likely due to inhibition of P‐gp‐mediated renal tubular secretion. Further evaluation of renal P‐gp‐modulating drugs such as itraconazole that may alter the renal excretion of coadministered drugs is warranted.

Evaluation of P-glycoprotein-mediated renal drug interactions in an MDR1-MDCK model.

Study Objective. To evaluate P‐glycoprotein (P‐gp)‐mediated renal drug interactions in an in vitro model of tubular secretion.

Effect of uremic serum and uremic toxins on drug metabolism in human microsomes

There is increasing evidence that renal impairment modifies nonrenal drug clearance through drug metabolizing cytochrome P450 (CYP) enzymes. In this study, the direct inhibitory effect of serum from chronic renal failure (CRF) patients receiving dialysis was evaluated in CYP3A4 (testosterone) and CYP2B6 (bupropion) metabolism assays. Human liver microsomes were incubated with ultrafiltered serum collected pre- and post-hemodialysis from ten CRF patients. Additionally, several uremic toxins were evaluated in the CYP3A4 assay. In only three patients was there a significant decrease or increase in testosterone or bupropion metabolism post-dialysis. Urea, mannitol, guanidine, homocysteine, uridine and creatinine had no effect on CYP3A4 metabolism. CMPF, hippuric acid and p-cresol had IC50 values that fell within CRF patient plasma concentrations. The IC50 values for indoxyl sulfate and indole-3-acetic acid were greater than CRF plasma concentrations. The lack of a consistent effect on CYP3A4 or CYP2B6 metabolism by uremic serum may be due in part to the frequency of hemodialysis in these patients which reduced the accumulation of uremic toxins. CMPF, hippuric acid and p-cresol have the ability to inhibit CYP3A4 metabolism at clinical concentrations which may correspond to reports of changes in hepatic metabolism in some CRF patients.