Renal function in cystic fibrosis: proteinuria and enzymuria before and after tobramycin therapy

Role of urinary NAG enzyme in early detection of renal impairment in cystic fibrosis patients

Background

Cystic fibrosis (CF) is the most common life-limiting autosomal recessive disease among people in the USA and Europe with increased prevalence in Egypt. Affected children are in danger of acute kidney injury and the development of chronic renal disease through exposure to multiple nephrotoxic agents. N-acetyl beta-D-glucosaminidase (NAG) is a lysosomal enzyme present in high concentrations in the proximal tubular cells, thus raising urinary NAG levels to reflect tubular dysfunction. The aim of our study is to detect the role of the urinary NAG enzyme in the early detection of renal impairment in CF patients. This cross-sectional study enrolled 40 CF patients diagnosed in the CF Clinic in Children’s Hospital of Cairo University. They were age- and sex-matched to 40 healthy controls. All patients had glomerular filtration rate (GFR), serum creatinine, blood urea nitrogen (BUN), albumin/creatinine (A/C) ratio measured, urine analysis, urinary NAG enzyme using enzyme-linked immunosorbent assay (ELISA), and renal ultrasound (U/S) were done.

Results

Our study showed high levels of urinary NAG in cases with a significant difference between cases and controls (P value < 0.001). There was a significant correlation between urinary NAG enzyme elevation and A/C ratio in urine, nephrotoxic drugs administration, and duration of disease (P value = 0.002, 0.005, 0.019), respectively.

Conclusion

Our study suggested that the NAG enzyme is a good early detector of renal impairment in CF patients before the conventional laboratory assays become deranged.

Pharmacokinetics and safety of tobramycin nebulization with the I-neb and PARI-LC Plus in children with cystic fibrosis: A randomized, crossover study

AIMS

We aimed to compare the pharmacokinetics (PK) and safety profile of tobramycin inhalation solution (TIS) using the I-neb device to the standard PARI-LC Plus nebulizer in children with cystic fibrosis.

METHODS

A randomized, open-label, crossover study was performed. In 2 separate study visits, blood samples from 22 children were collected following TIS nebulization with I-neb (75 mg) and PARI-LC Plus (300 mg). Study visits were separated by 1 month, in which 1 of the study nebulizers was used twice daily. Tobramycin PK for both nebulizers was established using measured tobramycin concentrations and Bayesian PK modelling software. Hearing and renal function tests were performed to test for aminoglycoside associated toxicity. In addition to standard estimated glomerular filtration rate values, biomarkers for tubular injury (KIM-1 and NAG) were measured. Patient and nebulizer satisfaction were assessed.

RESULTS

Inhalations were well tolerated and serum trough concentrations below the predefined toxic limit were reached with no significant differences in PK parameters between nebulizers. Results of audiometry and estimated glomerular filtration rate revealed no abnormalities. However, increased urinary NAG/creatinine ratios at visit 2 for both nebulizers suggest TIS-induced subclinical tubular kidney injury. Nebulization time was 50% shorter and patient satisfaction was significantly higher with the I-neb.

CONCLUSIONS

Nebulization of 75 mg TIS with the I-neb in children with cystic fibrosis resulted in comparable systemic exposure to 300 mg TIS with the PARI-LC Plus and was well tolerated and preferred over the PARI-LC Plus. Long-term safety of TIS nebulization should be monitored clinically, especially regarding the effects on tubular kidney injury.

Renal dysfunction in cystic fibrosis: is there cause for concern?

Most people associate cystic fibrosis (CF) with lung disease. Although this is the major cause of morbidity and mortality, CF is in fact a multi-organ disease. Patients with CF are living longer. Accompanying their increased life expectancy are complications not previously encountered. One of the less obvious concerns is that of renal dysfunction associated with long-term exposure to aminoglycosides as well as renally toxic immunosuppressants in lung transplant recipients. This article reviews what is known about the extent of the problem, summarizes what the current practices of measuring and monitoring renal function in patients with CF, and makes suggestions for alternative approaches. In particular, the potential role of cystatin C will be discussed.

Measurement of urinary N-acetyl-b-D-glucosaminidase in adult patients with cystic fibrosis: before, during and after treatment with intravenous antibiotics

BACKGROUND

Patients with cystic fibrosis (CF) are at high risk from the nephrotoxic effects of intravenous antibiotics due to repeated and prolonged courses of therapy. Routine methods of monitoring renal injury are insensitive. N-acetyl-b-d-glucosaminidase (NAG) is a lysosomal enzyme present in the renal proximal tubular cells, with increased excretion an indicator of renal tubular dysfunction.

METHODS

Urinary NAG, creatinine, serum creatinine, electrolytes and BUN were measured on days 1, 14 and at the first out-patient visit following treatment with tobramycin or colistin. Urinary NAG levels were corrected for urinary creatinine and expressed as a NAG ratio. Patients who received>1 course of intravenous antibiotics during the study period were included in a separate analysis of the cumulative effect of treatment.

RESULTS

88 patients (44 female, 31 with CFRD) completed a single course of intravenous antibiotics. 71 patients had urinary NAG levels at follow-up. The median time to follow-up was 50 days. Serum electrolytes, creatinine and BUN were normal throughout. A 3.5-fold increase in urinary NAG excretion was observed between day 1 and 14 and 46% of patients had an elevated NAG level at follow-up. A highly significant difference in NAG excretion was observed on day 14 for tobramycin vs. colistin (median 2.24 vs. 0.98, p<0.001). A significant difference in NAG excretion was seen in patients with CFRD at all measured time points. Patients with CFRD had a significantly worse clinical status and had received more days of intravenous antibiotics over the previous 6 years. In 20 (80%) of 25 patients who received>1 course of treatment during the study period, baseline NAG levels were significantly higher in subsequent courses (p<0.001). There was a significant correlation between previous exposure to colistin and baseline NAG levels (r=0.389, p<0.001).

CONCLUSIONS

Both tobramycin and colistin cause acute renal tubular injury with a significant rise in urinary NAG excretion. Patients with CFRD seem to be at greatest risk of renal tubular damage. Cumulative damage is evident with repeated dosing. Previous exposure to nephrotoxic antibiotics, especially colistin, is associated with elevated baseline NAG levels. We recommend that colistin is reserved for patients with resistant Pseudomonas aeruginosa or those who are intolerant to tobramycin. Serial longitudinal NAG measurements may be useful in patients with CF, especially those with CFRD, to identify patients at risk of developing renal disease.

The effects of intravenous tobramycin on renal tubular function in children with cystic fibrosis

BACKGROUND

Tobramycin, used to treat respiratory exacerbations in cystic fibrosis (CF), is also a renal tubular toxin. Tubular dysfunction leads to increased urinary levels of the proximal tubular lysosomal enzyme, N-acetyl-beta-D-glucosaminidase (NAG) and the proximal tubular protein, retinol-binding protein (RBP). Hypermagnesuria and resulting hypomagnesaemia are indicative of more severe tubular damage, occasionally seen following repeated courses of intravenous tobramycin. Using these biochemical markers we studied the effect of a 2-week course of this agent on tubular function.

METHODS

Twenty-two children (11 boys) with CF were studied. Median age = 10.9 years, range 3.1-16.4 years. All had a normal predicted glomerular filtration rate (pGFR). They received tobramycin 3 mg/kg/dose tds. Urinary NAG, RBP, creatinine and plasma magnesium and creatinine were assayed: a) immediately before commencing tobramycin, b) immediately following the course, c) 4 weeks after the end of the course.

RESULTS

Mean log UrNAG and UrRBP rose significantly between time points a) and b) before falling to almost pre-treatment levels by time c). Using two way ANOVA analysis the results for UrNAG and UrRBP were both highly statistically significant (p<0.0001). Paired t-tests on the logged values revealed highly significant differences between all time points for UrNAG and in the case of UrRBP for all other than a) compared to c). In all patients plasma magnesium and pGFR remained within normal limits.

CONCLUSIONS

Intravenous tobramycin produces acute tubular injury, which showed evidence of almost complete recovery after 4 weeks. The insult to the tubules was not sufficient to produce hypomagnesaemia in our study group. To assess cumulative tubular damage in more detail it would be necessary to repeat this study after further courses of tobramycin. We recommend monitoring plasma magnesium during courses of intravenous tobramycin.

Once versus three-times daily regimens of tobramycin treatment for pulmonary exacerbations of cystic fibrosis--the TOPIC study: a randomised controlled trial

BACKGROUND

Intravenous tobramycin (three-times daily) is widely used for pulmonary exacerbations in patients with cystic fibrosis who have chronic Pseudomonas aeruginosa infection. We undertook a double-blind, randomised controlled trial to assess the safety and efficacy of once versus three-times daily tobramycin in these patients.

METHODS

244 patients from 21 cystic-fibrosis centres in the UK were randomly assigned to once or three-times daily tobramycin (with ceftazidime) for 14 days. Treatment was given as 30-min infusions of tobramycin in 0.9% saline. Primary outcome measure was change in forced expiratory volume in 1s (FEV1), over the 14 days of treatment, expressed as a percentage of the predicted normal value for age, sex, and height. We also measured the change in FEV1 expressed as a percentage of baseline. Secondary outcomes included change in serum creatinine. The study was powered for equivalence, and primary analysis was per protocol.

FINDINGS

219 patients (107 once daily, 112 three-times daily) completed the study per protocol. None was lost to follow-up, although 20 discontinued intervention. Of 122 patients assigned to once daily treatment, three did not receive the study regimen. The mean change in FEV1 (% predicted) over 14 days was similar on the two regimens (10.4% [once daily] vs 10.0% [three-times daily]; adjusted mean difference 0.4% [95% CI -3.3 to 4.1]). Mean% change in FEV1 from baseline was also similar in both treatments (21.9% vs 22.1%; -0.1% [-8.0 to 7.9]). There was no significant difference in% change in creatinine from baseline (-1.5% [once daily] vs 1.7% [three-times daily]). However, in children, once daily treatment was significantly less nephrotoxic than was thrice daily (mean% change in creatine -4.5% [once daily] vs 3.7% [thrice daily]; adjusted mean difference -8.0%, 95% CI -15.7 to -0.4). No patients developed hearing loss during the study, although two reported acute dizziness and were withdrawn from the study.

INTERPRETATION

Intravenous tobramycin has equal efficacy if given once or three-times daily (with ceftazidime) for pulmonary exacerbations of cystic fibrosis. The once daily regimen might be less nephrotoxic in children.

Microalbuminuria as a screening tool in cystic fibrosis-related diabetes

The improving longevity of cystic fibrosis (CF) subjects has resulted in an increased prevalence and duration of cystic fibrosis-related diabetes (CFRD). Microvascular complications were reported in CFRD. Microalbuminuria is well-established as a sensitive indicator of progression to diabetic nephropathy in non-CF diabetes, but confounding factors may make it less sensitive for CF subjects. We performed a cross-sectional study to look for the presence of microalbuminuria in samples from 40 CF subjects (34 without diabetes; CFND) attending the Exeter CF Clinic, compared with 43 nondiabetic, non-CF controls. The albumin-creatinine ratio (ACR) was raised in CF subjects both with (P < 0.001) and without (P < 0.0001) diabetes compared to controls. This reflected an increase in urinary albumin and a reduction in urinary creatinine in CF subjects. In single samples, microalbuminuria was present in 66.7%, 32.4%, and 15.4% of subjects in CFRD, CFND, and control groups. Repeat samples showed that 12% of CFND subjects and 17% of CFRD subjects met the criteria for a diagnosis of persistent microalbuminuria. In conclusion, CF subjects, even when not diabetic, have increased urinary albumin excretion due to chronic infection, and reduced urinary creatinine excretion due to low muscle mass. This results in subjects, who are not developing diabetic nephropathy, meeting the conventional criteria for microalbuminuria. We feel that further studies are required to clarify whether this measure is a useful tool to predict progression to diabetic nephropathy in subjects with CFRD.

Renal impairment in cystic fibrosis patients due to repeated intravenous aminoglycoside use

Although there are reports of cases of acute renal failure occurring in cystic fibrosis (CF) patients, usually in association with the use of nephrotoxic antibiotic therapy, there have been no studies of renal function in this patient group. We hypothesized that long-term use of intravenous (IV) nephrotoxic antibiotics (aminoglycosides and colistin sulphomethate) may contribute to renal disease in CF patients. In a prospective study, we assessed creatinine clearance as an index of renal function with two techniques (24-hr urine collections and the Cockroft-Gault formula) in a group of 80 stable adult CF outpatients chronically infected with Pseudomonas aeruginosa but with no history of preceding renal disease. Using a multiple linear regression model, we evaluated their renal function in terms of their lifetime IV use of aminoglycosides and colistin. Between 31% (Cockroft-Gault formula method) and 42% (24-hr urine collection method) of patients had a creatinine clearance below normal range. Using either method, there was a strong correlation between aminoglycoside use and diminishing renal function (r=- 0.32, P=0.0055), which was potentiated by the coadministration of colistin (r=- 0.42, P <0.0002). However, there was no correlation with colistin when used in combination with other antibiotics alone (r=0.18, P=NS). Repeated IV aminoglycoside use in CF is associated with long-term renal damage. Although this effect is potentiated by colistin, colistin on its own in moderate doses does not appear to be nephrotoxic. IV aminoglycosides should be used cautiously in CF patients, with regular monitoring of renal function.

[Antibiotic therapy in cystic fibrosis. II Antibiotic strategy]

Antibiotherapy is one of the main treatments of cystic fibrosis, contributing to a better nutritional and respiratory status and a prolonged survival. The choice of antibiotics depends on quantitative and qualitative analysis of sputum, bacteria resistance phenotypes and severity of infection. Haemophilus influenzae infection can be treated orally with the association of amoxicillin-clavulanic acid or a cephalosporin. Staphylococcus aureus generally remains sensitive to usual antibiotics; in case of a methicillin-resistant strain, an oral bitherapy or a parenteral cure can be proposed. Treatment of Pseudomonas aeruginosa is different in case of first colonization or chronic infection: in first colonization, parenteral antibiotherapy (beta-lactams-aminoglycosids) followed by inhaled antibiotherapy may eradicate the bacteria; in chronic infections, exacerbations require parenteral bi-antibiotherapy (beta-lactams or quinolons and aminoglycosids) for 15 to 21 days, inhaled antibiotics between the cures being useful to decrease the number of exacerbation. A careful monitoring of antibiotherapy is necessary because of possible induction of bacterial resistance, nephrotoxicity and ototoxicity of aminosids and allergy to beta-lactams.

Urinary N-acetyl-beta-D-glucosaminidase activity in patients with cystic fibrosis on long-term gentamicin inhalation

OBJECTIVE

To investigate possible renal toxicity of long-term gentamicin inhalation in patients with cystic fibrosis.

METHODS

Urinary N-acetyl-beta-D-glucosaminidase (NAG) activity was measured during routine respiratory clinic visits. Outpatient records were reviewed for data on long-term gentamicin inhalation, and parents and patients were interviewed for compliance. Exclusion criteria were irregular gentamicin inhalation, urinary infection or other febrile illness, intravenous aminoglycoside treatment during the previous three months, and diabetes mellitus. Patients were assigned to three groups: group 1, current gentamicin inhalation; group 2, previous gentamicin inhalation that had been stopped at least three months ago; and group 3, never any gentamicin inhalation.

RESULTS

52 patients (34 girls, 18 boys), mean (SD) age 11.5 (5.7) years, entered the study. Patients currently on gentamicin inhalation (n = 20) were significantly younger and had higher urinary NAG activity (0.83 (0.57) U/mmol creatinine) than the 23 patients without gentamicin inhalation (0.26 (0.10) (p = 0.0001) and the nine patients with previous gentamicin inhalation (0.32 (0.15) (p = 0.0125). Twelve patients on current gentamicin inhalation had raised NAG values but all those in groups 2 and 3 had NAG values within the normal range. In patients currently on gentamicin inhalation, there was a positive correlation between urinary NAG activity and cumulative dose of nebulised gentamicin (r = 0.60, p = 0.0049).

CONCLUSIONS

Long-term gentamicin inhalation in patients with cystic fibrosis poses a risk of renal toxicity. It is not known whether further treatment might result in more severe renal damage.

Estimation of ifosfamide/cisplatinum-induced renal toxicity by urinary protein analysis

Ifosfamide (IFO) chemotherapy has been reported to result in deToni-Debré-Fanconi syndrome in a minority of patients only, but evaluation of tubular transport capacities has identified a substantial number of patients as having subclinical tubular dysfunction. After completion of combination chemotherapy employing IFO (n = 37) or IFO plus cisplatinum (CPL) (n = 27), glomerular and tubular function was assessed in 64 patients by the urinary excretion of transferrin, IgG, albumin, alpha 1-microglobulin (A1M) and N-acetyl-beta-D-glucosaminidase. Sodium dodecyl sulphate polyacrylamide gel electrophoresis was performed in 21 patients. The determination of urinary marker proteins was compared with the glomerular filtration rate, the fractional phosphate and percent amino acid reabsorption. A reduced glomerular filtration rate was observed in 9.8% of patients. Tubular dysfunction was frequent, with a predominance of renal amino acid (57%) and A1M (48%) loss. IFO-mediated renal toxicity was dose dependent. CPL treatment resulted in significant enhancement of tubular toxicity induced by IFO, whereas concomitant gentamicin therapy did not affect tubular function. Measurement of urinary protein cannot replace other tests for tubular dysfunction in IFO-treated patients, because the spectrum of IFO-induced nephrotoxicity includes dysfunction of different and independent transport mechanisms of the proximal tubular system. Increased urinary A1M excretion is an important indicator of impaired tubular protein reabsorption.

Renal involvement in patients with congenital cyanotic heart disease

Patients with congenital cyanotic heart disease may develop a glomerulopathy with proteinuria and impaired renal function. In order to investigate this problem we conducted a study on 27 patients with uncorrected cyanotic heart disease who were between 1 day and 25 years old. As a consequence of hypoxaemia haematocrit was elevated to 57%. Proteinuria was above 150 mg/day/1.73 m2 body surface in 12 patients. Only one of 9 children under 10 years of age had pathological proteinuria presenting as isolated albuminuria. Seven out of 10 patients between 11 and 20 years had an elevated proteinuria with a glomerular pattern. Creatinine clearance was normal in these patients. All four patients above 20 years of age had a considerable glomerular proteinuria with a mean excretion of 5.7 g/24 h/1.73 m2 body surface. These patients suffered additionally from chronic cardiac failure and creatinine clearance was below the normal range. There was a clear relationship between pathological proteinuria and age of the patients and thus duration of hypoxaemia. Patients with pathological proteinuria had a significant higher erythrocyte count (7.3 +/- 1.3 vs 5.6 +/- 1.4 10(12)/l p less than 0.01) and a lower mean corpuscular haemoglobin. In summary, children with persistent congenital cyanotic heart disease have substantial risk of developing a glomerulopathy if the cyanosis remains unchanged for more than ten years.

Long-term tobramycin aerosol therapy in cystic fibrosis

The long-term efficacy and safety of aminoglycoside aerosol therapy for Pseudomonas aeruginosa colonization/infection in cystic fibrosis has not been fully investigated. In the present study, 14 patients with cystic fibrosis, ages 8-19 years (mean: 13.3 years), received tobramycin aerosol therapy for a mean duration of 20 months. Eighty milligrams of a tobramycin solution were inhaled twice daily after physiotherapy via a jet nebulizer. After 1 year, weight for height increased significantly by 2.9% of the predicted normal, and the Kraemer clinical score increased by 2.1 points (P less than 0.05). The frequency of hospital admissions decreased from 2.0 to 1.3 per patient, respectively, during the years before and after the study onset. The antibody response to P. aeruginosa elastase, exotoxin A, and alkaline phosphatase showed a reduction in serum titers against one or more enzymes in eight patients. The best long-term results after 12-38 months of treatment were obtained in moderately ill children. No evidence of ototoxicity or renal damage was observed. Although intermittent bacterial resistance occurred in five patients after 10-21 months of tobramycin inhalation, this was not associated with clinical deterioration. The study demonstrates the safety and clinical efficacy of long-term tobramycin aerosol therapy. Double-blind studies with larger patient cohorts are required to determine the value of aminoglycoside inhalation as an adjunct to the established therapeutic regimens.