Assessment of the enzymuria resulting from gentamicin alone and combinations of gentamicin with various beta-lactam antibiotics

The Diagnostic Role of Urinary N-Acetyl-β-D-glucosaminidase (NAG) Activity in the Detection of Renal Tubular Impairment

The kidney function can be assessed by a number of methods. The urinary excretion of enzymes, in particular N-acetyl-β-D-glucosaminidase (NAG), is considered a relatively simple, cheap, fast and non-invasive method in the detection and follow-up of renal tubular function under various conditions. The determination of urinary NAG provides a very sensitive and reliable indicator of renal damage, such as injury or dysfunction due to diabetes mellitus, nephrotic syndrome, inflammation, vesicoureteral reflux, urinary tract infection, hypercalciuria, urolithiasis, nephrocalcinosis, perinatal asphyxia, hypoxia, hypertension, heavy metals poisoning, treatment with aminoglycosides, valproate, or other nephrotoxic drugs. This paper gives an overview of the current use of urinary NAG in the detection of renal injury.

Serum cystatin C level for better assessment of glomerular filtration rate in cystic fibrosis patients treated by amikacin

BACKGROUND AND OBJECTIVE

Monitoring of renal function in cystic fibrosis (CF) patients is essential. The dosage regimen of amikacin is regularly modified according to the patient's glomerular filtration rate (GFR). The aim of the study was to evaluate the use of cystatin C (CyC) for monitoring amikacin therapy along with other markers of renal tubular and glomerular function, and damage [N-acetyl-beta-d glucosaminidase (NAG), creatinine level and creatinine clearance].

METHODS

We compared the GFR, estimated from the serum concentrations of creatinine (Cockcroft-Gault formula) and CyC (Grubb's formula). Seventy-one patients (mean age 12 years; range 4-28 years) with CF were treated by intermittent intravenous infusion of amikacin. Tubular nephrotoxicity was investigated by measurement of urine NAG/urine creatinine ratio (U-NAG/U-creatinine). Concentrations of all markers were measured before starting amikacin therapy and at days 3, 5, 7, 10 and 12. Fluorescence polarization analysis, turbidimetry, enzymatic phototometric creatinine deaminase method and fluorimetry were used for determination of serum amikacin, serum CyC, creatinine and urine NAG activity. Receiver operating characteristic (ROC) analysis was performed to assess the influence of GFR estimated from serum creatinine and serum CyC for the prediction of amikacin clearance during aminoglycoside therapy.

RESULTS

Significant differences in the rate of U-NAG/U-creatinine were noted before and after treatment with amikacin (P < 0.001). Serum creatinine levels and creatinine clearance at the end of amikacin therapy (12th day) did not show any significant differences in comparison with the levels measured before the start of therapy (0th day). At days 5, 7, 10 and 12, serum CyC levels showed a significant elevation (P < 0.001), and CyC clearance showed a significant decrease (P < 0.001) in comparison with the levels measured at day 0. The ratio of amikacin clearance/creatinine clearance decreased with therapy whereas the amikacin clearance/CyC and amikacin clearance/CyC clearance increased.

CONCLUSION

We showed that the rate of U-NAG/U-creatinine is a suitable marker for monitoring tubular nephrotoxicity in CF patients. Serum creatinine and estimated creatinine clearance are modest predictors of GFR in CF patients. CyC appears to be a better marker of GFR than serum creatinine concentration or creatinine clearance in our study. Serum CyC levels and CyC clearance showed greater ability to predict amikacin clearance during therapy than creatinine clearance.

Diagnosis, epidemiology and outcomes of acute kidney injury

Acute kidney injury is an increasingly common and potentially catastrophic complication in hospitalized patients. Early observational studies from the 1980s and 1990s established the general epidemiologic features of acute kidney injury: the incidence, prognostic significance, and predisposing medical and surgical conditions. Recent multicenter observational cohorts and administrative databases have enhanced our understanding of the overall disease burden of acute kidney injury and trends in its epidemiology. An increasing number of clinical studies focusing on specific types of acute kidney injury (e.g., in the setting of intravenous contrast, sepsis, and major surgery) have provided further details into this heterogeneous syndrome. Despite our sophisticated understanding of the epidemiology and pathobiology of acute kidney injury, current prevention strategies are inadequate and current treatment options outside of renal replacement therapy are nonexistent. This failure to innovate may be due in part to a diagnostic approach that has stagnated for decades and continues to rely on markers of glomerular filtration (blood urea nitrogen and creatinine) that are neither sensitive nor specific. There has been increasing interest in the identification and validation of novel biomarkers of acute kidney injury that may permit earlier and more accurate diagnosis. This review summarizes the major epidemiologic studies of acute kidney injury and efforts to modernize the approach to its diagnosis.

Antibiotic-related renal failure and cystic fibrosis

Recently published reports suggest that the combination of aminoglycosides with ceftazidime may increase the risk of renal disease in cystic fibrosis. We describe a case of unusually severe acute tubular necrosis occurring in an adolescent with cystic fibrosis receiving i.v. gentamicin plus ceftazidime and discuss the possible mechanisms.

Effect of once-daily dosing vs. multiple daily dosing of tobramycin on enzyme markers of nephrotoxicity

OBJECTIVE

To determine the incidence of nephrotoxicity of once-daily dosing (ODD) and multiple daily dosing (MDD) regimens of tobramycin in critically ill patients.

DESIGN

Randomized, prospective clinical trial.

SETTING

: Adult intensive care units at two university hospitals.

PATIENTS

Fifty-eight critically ill patients with a suspected or documented aerobic Gram-negative infection.

INTERVENTIONS

Patients were randomized to receive tobramycin by ODD (7 mg/kg) or MDD. Baseline urine aliquots and 24-hr urine collections were collected on days 3, 7, and 11 during therapy and on days 3, 7, and 11 following discontinuation of therapy for measurement of alanine aminopeptidase (AAP), N-acetyl-beta-d-glucosaminidase (NAG), and creatinine.

MEASUREMENTS AND MAIN RESULTS

Fifty-four patients were evaluable (ODD n = 25; MDD n = 29). The groups were similar with regard to demographic and clinical variables. The tobramycin dose was higher in the ODD group compared with the MDD group (425 +/- 122.5 mg vs. 312.8 +/- 116.6 mg, p <.001). Patients in the MDD group received a mean of 3.89 +/- 1.14 mg.kg(-1)day(-1) at intervals of 11.92 +/- 3.12 hrs. In the ODD group, patients had a higher measured creatinine clearance at the end of therapy compared with MDD group (70 +/- 18.6 vs. 64.8 +/- 17.5 mL/min, p =.047). Fewer patients in the ODD group developed nephrotoxicity than the MDD group (5 vs. 12, p =.142). Although there were increases in urinary enzymes in both treatment groups (AAP, 8.7 +/- 2.9 vs. 5.2 +/- 2.1 units/24 hrs, p <.01 MDD vs. ODD; NAG, 14.7 +/- 4.9 vs. 6.8 +/- 3.1, p <.01 MDD vs. ODD), the increases in the ODD group were significantly lower than in the MDD group.

CONCLUSIONS

: The ODD tobramycin regimen appeared to be less nephrotoxic than the MDD regimen despite significantly higher doses. Tobramycin administered by ODD may be the preferred dosing method in selected critically ill medical patients to reduce the incidence and extent of renal damage.

Urinary N-acetyl-beta-D-glucosaminidase activity in healthy children

AIM

The principal aim was to establish paediatric reference data for the urinary N-acetyl-beta-D-glucosaminidase (U-NAG) activity.

METHOD AND RESULTS

Two hundred and sixty-two healthy children aged 0-18 years (0-1 month, n = 38; 1 month-1 year, n = 50; 1-3 years, n = 50; 3-6 years, n = 46; 6-10 years, n = 29; 10-18 years, n = 49) had a urine sample collected and the U-NAG activity was evaluated by using fluorimetry and related to urinary creatinine as a nkat/mmol ratio. A strong age dependence of the U-NAG/creatinine ratio and its high interindividual variability in children was observed; the highest values of upper reference range being in the 0-1 month and 1 month-1 year groups (134.8 and 50, respectively), which dropped gradually to 7.25 in the oldest age group (10-18 years).

CONCLUSION

The establishment of urinary NAG reference paediatric values is a potentially useful tool for the proper evaluation of renal tubular impairment in children.

Pneumoperitoneum does not potentiate the nephrotoxicity of aminoglycosides in rats

OBJECTIVES

Pneumoperitoneum is associated with transient renal dysfunction. To our knowledge, the safety of administering nephrotoxins such as aminoglycosides during pneumoperitoneum has not been studied. Our hypothesis was that pneumoperitoneum potentiates the nephrotoxicity of aminoglycosides.

METHODS

From 29 rats we obtained preprocedure 24-hour urine collections. In the pneumoperitoneum group (n = 7), carbon dioxide was insufflated intra-abdominally at 15 mm Hg pressure for 2 hours. In the gentamicin group (n = 7), 10 mg/kg gentamicin was administered intravenously. In the combined pneumoperitoneum/gentamicin group (n = 8), the same dose of gentamicin was administered 10 minutes before pneumoperitoneum. Sham rats (n = 7) received anesthesia only. Urine was collected for the 24 hours after the procedure, and 1 week later blood for creatinine determination and final 24-hour urine collections were obtained. All urine samples were assayed for creatinine and N-acetyl-beta-glucosaminidase (NAG).

RESULTS

Only the gentamicin and combined pneumoperitoneum/gentamicin groups presented day 1 values for NAG excretion that were significantly greater than same day sham or paired preprocedure values; the rest of the urinary creatinine and NAG day 1 levels and all the day 7 levels were not significantly different from same day sham or paired preprocedure levels. Day 7 serum creatinine and creatinine clearance did not differ significantly among the groups.

CONCLUSIONS

We found that intravenous gentamicin transiently increased urinary excretion of NAG in rats, which resolved within 1 week. Pneumoperitoneum for 2 hours at 15 mm Hg did not increase urinary NAG, either alone or in gentamicin-treated rats. Moreover, our data are sufficient to refute with 95% certainty the possibility that gentamicin plus pneumoperitoneum decreases creatinine clearance more than approximately 60%. These results do not support the hypothesis that pneumoperitoneum potentiates the nephrotoxicity of aminoglycosides.