Alanine aminopeptidase and beta 2-microglobulin excretion in patients receiving vancomycin and gentamicin

The renoprotective effect of concomitant fosfomycin in the treatment of pulmonary exacerbations in cystic fibrosis

Background

Fosfomycin, effective in Cystic Fibrosis (CF), competes with aminoglycosides at renal binding sites and may therefore afford a renoprotective effect when used in combination therapy. We explored this by using markers of acute renal tubular damage [N-acetyl-β-d-glucose-aminidase (NAG), alanine amino-peptidase (AAP) and β₂-microglobulin].

Methods

Using a prospective randomized crossover trial design, at an acute pulmonary exacerbation, 18 adult CF patients received either 14 days of intravenous (IV) tobramycin or IV tobramycin and IV fosfomycin, both in combination with a second IV antibiotic (colomycin).

Results

Urinary NAG (P = 0.003) and AAP (P = 0.03) following treatment with concomitant fosfomycin were lower than those after treatment with tobramycin and colomycin alone. Fosfomycin attenuated the total 24-h urinary protein leak (P = 0.0001). The 14-day improvements in all surrogate markers of exacerbation resolution (FEV₁% predicted, FVC, white cell count and C-reactive protein) were similar for both treatment regimens.

Conclusion

The addition of fosfomycin reduces acute renal injury caused by IV aminoglycoside therapy in CF pulmonary exacerbations.

Urinary clusterin, cystatin C, beta2-microglobulin and total protein as markers to detect drug-induced kidney injury

Earlier and more reliable detection of drug-induced kidney injury would improve clinical care and help to streamline drug-development. As the current standards to monitor renal function, such as blood urea nitrogen (BUN) or serum creatinine (SCr), are late indicators of kidney injury, we conducted ten nonclinical studies to rigorously assess the potential of four previously described nephrotoxicity markers to detect drug-induced kidney and liver injury. Whereas urinary clusterin outperformed BUN and SCr for detecting proximal tubular injury, urinary total protein, cystatin C and beta2-microglobulin showed a better diagnostic performance than BUN and SCr for detecting glomerular injury. Gene and protein expression analysis, in-situ hybridization and immunohistochemistry provide mechanistic evidence to support the use of these four markers for detecting kidney injury to guide regulatory decision making in drug development. The recognition of the qualification of these biomarkers by the EMEA and FDA will significantly enhance renal safety monitoring.

Biomarkers of nephrotoxic acute kidney injury

Acute kidney injury (AKI) is a common condition with significant associated morbidity and mortality. Epidemiologic data suggest that a significant proportion of AKI cases is at least partially attributable to nephrotoxin exposure. This is not surprising given intrinsic renal susceptibility to toxicant-induced injury, a consequence of the unique physiologic and biochemical properties of the normally functioning kidney. A number of pathophysiologic mechanisms have been identified that mediate toxic effects on the kidney, resulting in a variety of clinical syndromes ranging from subtle changes in tubular function to fulminant renal failure. Unfortunately, standard metrics used to diagnose and monitor kidney injury, such as blood urea nitrogen and serum creatinine, are insensitive and nonspecific, resulting in delayed diagnosis and intervention. Considerable effort has been made to identify biomarkers that will allow the earlier diagnosis of AKI. Further characterization of these candidate biomarkers will clarify their utility in the setting of acute nephrotoxicity, define new diagnostic and prognostic paradigms for kidney injury, facilitate clinical trials, and lead to novel effective therapies.

Nephrotoxicity due to Combination Antibiotic Therapy with Vancomycin and Aminoglycosides in Septic Critically Ill Patients

The aim of this prospective observational study was to evaluate the incidence of nephrotoxicity due to combination therapy with vancomycin and aminoglycosides in septic critically ill patients admitted to the intensive care unit.

METHODS

Thirty consecutive critically ill patients were treated with vancomycin concurrent with aminoglycosides for sepsis. Inclusion criteria were: the need for mechanical ventilation and the presence of severe infection due to bacteria susceptible to vancomycin and aminoglycosides. Exclusion criteria were: age <18 years, impaired renal function (24-hour creatinine clearance <90 ml/min) or previous adverse reaction to either drug. Serum creatinine and urea concentrations, creatinine clearance, 24-hour urinary excretion of proteins, beta2-microglobulin and enzymes were measured immediately before starting therapy and at different times thereafter.

RESULTS

Eleven of the 30 patients had a transient and modest increase in serum urea, 15 patients presented with urinary excretion of beta2-microglobulin and tubular enzymes, and 14 patients had urinary proteins. In the only patient with severe acute renal failure (serum creatinine 8.2 mg/dl), the clinical course was complicated by prolonged hypotension.

CONCLUSION

Concurrent administration of vancomycin and aminoglycosides to critically ill septic patients with normal renal function at baseline induced mainly slight and transient toxic tubular effects. The only clinically significant nephrotoxic event occurred in a patient with septic shock.

Pharmacodynamic characterization of nephrotoxicity associated with once-daily aminoglycoside

STUDY OBJECTIVE

To characterize nephrotoxicity associated with an individualized serum concentration target-specific, once-daily aminoglycoside (ODA) program.

DESIGN

Concurrent and retrospective study.

SETTING

University-affiliated trauma hospital.

PATIENTS

Two hundred patients treated with ODA and 100 treated with individualized traditional dosing (TDA).

INTERVENTIONS

Empiric dosing for both groups was based on patient-specific pharmacokinetics and severity of infection. Regimens were modified according to predetermined target maximum and minimum serum concentrations for both groups.

MEASUREMENTS AND MAIN RESULTS

Nephrotoxicity occurred in 7.5% patients treated with ODA and 14.7% receiving TDA (p=0.05). Minimum serum concentrations, length of aminoglycoside therapy, and cumulative area under the curve (AUC) were all dependently related to nephrotoxicity, and concomitant vancomycin and other nephrotoxic drugs were independently related to the disorder. The cumulative AUC was greatest in patients receiving TDA (p=0.03), and the modeled probability of becoming toxic at any given cumulative AUC was significantly greater with TDA than with ODA (p<0.01). Clinical and microbiologic outcomes were similar between groups. Maximum concentration:minimum inhibitory concentration ratios were higher (p<0.01) and number of days to organism eradication was shorter in the ODA group (p=0.04).

CONCLUSION

The trend was toward decreased nephrotoxicity in patients treated with ODA compared with TDA, and at any given cumulative AUC, the risk of toxicity was lower for ODA.

Low molecular weight proteins in children with renal disease

Low molecular weight proteins are of interest in children because their increased urinary excretion is a sign of renal tubular disease and their increased plasma concentration is inversely related to glomerular filtration rate. These proteins include beta 2-microglobulin (B2M), retinol-binding protein (RBP), alpha 1-microglobulin (A1M) and lysozyme. B2M is unstable in acid urine, in contrast to RBP and A1M which are more stable. Any increase in the urinary excretion of B2M or RBP is highly specific for tubular disease, whereas increased excretion of A1M may be seen with glomerular proteinuria. Areas of clinical application include tubular and glomerular diseases, detection of drug toxicity, reflux nephropathy, birth asphyxia and insulin-dependent diabetes mellitus. Methods of sample collection and analysis of these proteins are discussed.

Chrononephrotoxicity in Rat of a Vancomycin and Gentamicin Combination

The effect of time of administration on excretion of two brush border enzymes--alanine aminopeptidase (AAP) and gamma-glutamyl transferase (gamma GT), and a lysosomal enzyme, N-acetyl-beta-D-glucosaminidase (NAG) with a single high dose of vancomycin, gentamicin or a combination of vancomycin and gentamicin was studied in male Wistar rats and compared with elimination of a control group. The rats received vancomycin intraperitoneally (200 mg.kg-1), gentamicin intramuscularly (100 mg.kg-1) or the combination of the drugs by the same route. A control group received isotonic NaCl solution. The four groups of animals received a single injection at 8 a.m., 2 p.m., 8 p.m., and 2 a.m. and urine excretion values for AAP, gamma GT and NAG were determined 24 hr later. The results show that the nephrotoxicity of gentamicin + vancomycin is greater than that observed with gentamicin, which again is greater than that observed with vancomycin. Furthermore, circadian variations in renal toxicity were observed, the least occurring at 8 a.m.

Enzymuria in neonates receiving continuous intravenous infusion of gentamicin

Urinary excretion of the tubular enzymes NAG and AAP was investigated during gentamicin treatment of 105 newborn infants. The values found for NAG and AAP show a significant positive correlation. The urinary excretion of NAG was on the average 92% higher during gentamicin treatment as compared with non-treatment periods in the same newborn infant (33 infants). The same tendency applied to AAP. Newborn infants receiving continuous intravenous infusion of gentamicin were not found to be at greater risk of nephrotoxicity than those receiving intermittent gentamicin treatment, using NAG and AAP as an index of nephrotoxicity. The changes in NAg and AAP within treatment periods were studied. During gentamicin treatment an insignificant average increase in the urinary excretion of NAG occurred, whereas a significant decrease was found during non-treatment periods. A significant negative correlation was found between urinary excretion of NAG and birth weight/gestational age. The long-term effect of the higher excretion of NAG and AAP in newborn and adult patients during aminoglycoside treatment is unknown.

Characterization of dipeptidyl and tripeptidyl aminopeptidases in human kidney soluble fraction

In an attempt to identify improved biochemical markers for the diagnosis of early kidney damage via urinary analysis of kidney derived enzymes, we have undertaken the systematic identification, quantification and characterization (following purification via anion exchange and gel filtration chromatography, and preparative electrophoresis) of the dipeptidyl and tripeptidyl aminopeptidases in normal human kidney soluble extract (with which the majority of the cellular activity of these enzymes is associated). Four chromatographically separable enzyme types were identified as follows (% relative activity in parentheses): dipeptidyl aminopeptidase I (EC 3.4.14.1; 24%); dipeptidyl aminopeptidase II (EC 3.4.14.2; 8%); dipeptidyl aminopeptidase IV (EC 3.4.14.5; 61%); tripeptidyl aminopeptidase (unclassified; 7%). Comparison of the levels of activity for the above enzyme types in normal and pathological urine may lead to an improvement upon existing procedures for the early detection of renal damage.

Pathogenic factors in aminoglycoside-induced nephrotoxicity

Aminoglycoside antibiotics play an integral role in antimicrobial chemotherapy. Unfortunately, these drugs are known to cause nephrotoxicity in man and experimental animals. In fact, the incidence of renal dysfunction during the course of clinical treatment with aminoglycoside antibiotics is approximately 10%. Over the past two decades the elucidation of the pathogenesis of aminoglycoside-induced nephrotoxicity has been the subject of numerous investigations. This review describes the recent theories postulated to play a role in the pathogenesis of antibiotic-induced renal damage. In particular, the importance of amino-glycoside levels in the renal cortex or at the membrane binding site is examined in detail. The relevance of antibiotic tissue levels is reflected in the ability of other drugs to modify nephrotoxicity through an alteration in renal aminoglycoside content. The role of factors including age and diet in drug-induced nephrotoxicity is described. In clinical practice, aminoglycoside antibiotics may often be with other agents. The influence of aminoglycoside interaction with other drugs including vancomycin, cephalosporins and cytotoxic drugs is examined in the light of reports that nephrotoxicity is potentiated in these situations. In addition, this review focuses on the role of infection (pyelonephritis and septicemia) and bacterial endotoxin as pathogenic factors involved in aminoglycoside nephrotoxicity. Both the direct influence of endotoxin and the indirect effects of vasoactive mediators and inflammatory processes will be discussed. A multiplicity of factors is involved in the pathogenesis of aminoglycoside-induced nephrotoxicity and these are further amplified in the presence of infection.

Vancomycin pharmacokinetics in burn patients and intravenous drug abusers

The pharmacokinetics of vancomycin were evaluated in 34 patients (10 burn patients, 14 intravenous drug abusers [IVDA], and 10 controls). Multiple serum samples were drawn following a 1-h vancomycin infusion at steady state over an 8- to 12-h dosing interval. Pharmacokinetic parameters were derived by noncompartmental analysis. There were no significant differences among the groups with respect to age, weight, serum creatinine, volume of distribution, or protein binding. Burn patients had a significantly higher creatinine clearance than did IVDA or controls. Vancomycin clearances averaged 142.8, 98.0, and 67.7 ml/min in burn patients, IVDA, and controls, respectively. The renal clearance of vancomycin was also higher in burn patients than in the other groups. IVDA tended to have a higher vancomycin clearance (31% higher) than did controls, but the difference was not statistically significant. Vancomycin clearance was much higher in burn patients requiring dosage individualization and close monitoring. A considerable amount of vancomycin was eliminated through renal tubular secretion, making dosage predictions based on creatinine clearance more difficult. Further work with IVDA will be needed to determine if they represent a group requiring aggressive vancomycin dosages.

Characterization of aminopeptidases in human kidney soluble fraction

Fractionation of human kidney soluble extract (with which the majority of cellular aminopeptidase activity is associated) via anion exchange chromatography resolved four types of separable aminopeptidase (relative activity in parenthesis): alanyl aminopeptidase (EC 3.4.11.14; 50%); arginyl aminopeptidase (EC 3.4.11.6; 30%); leucyl aminopeptidase (EC 3.4.11.1; 18%) and pyroglutamyl aminopeptidase (EC 3.4.19.3; 2%). The further purification (via gel filtration chromatography and preparative electrophoresis) and characterization of each aminopeptidase has been described; the aminopeptidase tissue profile for human kidney was found to be similar to that previously obtained for human skeletal muscle and brain tissue using a similar experimental approach, i.e. the same enzymes, with corresponding similar characteristics, are present in each tissue. These results suggest that soluble aminopeptidases may be of fundamental importance in general cell protein catabolism. Degradation of the following aminoacyl-AMC derivatives via kidney soluble extract has been shown to be due principally to hydrolysis by alanyl aminopeptidase: glutamyl, glycyl, isoleucyl, methionyl, ornithyl, phenylalanyl, prolyl, seryl, tyrosyl and valyl. We would suggest that measurement of the soluble extract-derived aminopeptidases described in this paper in urine may lead to an improvement upon existing assay procedures for early detection of kidney damage.

Gentamicin-induced renal metabolic alterations in newborn rat kidney: lack of potentiation by vancomycin

Daily subcutaneous administration of 20 or 100 mg/kg gentamicin for 4 days significantly decreased pyridoxal-5'-phosphate and lysosomal specific phosphatidylinositol-phospholipase C (PI-PLC) in newborn rat kidney. The fall in PI-PLC was associated with an elevation in renal phosphatidylinositol, phosphatidylserine, and phosphatidylcholine. The 100 mg/kg gentamicin dose also produced a rise in renal sphingomyelin, phosphatidylethanolamine, phosphatidylglycerol, and total phospholipid (TPL) accompanied by inhibition in the activities of Na+,K+-ATPase and alkaline phosphatase. In contrast, daily intraperitoneal injection of 100 mg/kg vancomycin for 4 days failed to markedly alter renal metabolic parameters. However, the 500 mg/kg vancomycin dose increased kidney weight, TPL, and all individual phospholipid class concentrations accompanied by inhibition of lysosomal specific PI-PLC activity and reduced pyridoxal-5'-phosphate levels. Simultaneous administration of 20 mg/kg gentamicin with either vancomycin dose resulted in renal alterations similar to those produced by gentamicin alone. Concurrent treatment with 100 mg/kg aminoglycoside and either vancomycin dose produced changes in kidney which were similar to those produced by gentamicin alone, except for a synergistic rise in PI as well as a greater fall in alkaline phosphatase and pyridoxal-5'-phosphate. Surprisingly, the concentration of gentamicin and vancomycin was less in newborn kidneys of rats receiving a simultaneous high dose of vancomycin and aminoglycoside treatment compared to levels found in animals given either antibiotic separately. The lack of potentiation of nephrotoxicity in newborns administered a combination of vancomycin and gentamicin may be due to decreased accumulation of either antibiotic in kidney.