Tubular nephrotoxicity during long-term ifosfamide and mesna therapy

Use of precision-cut renal cortical slices in nephrotoxicity studies

1.Unlike cell lines and primary cells in culture, precision-cut tissue slices remain metabolically differentiated for at least 24-48 h and allow to study the effect of xenobiotics during short-term and long-term incubations. 2.In this article, we illustrate the use of such an experimental model to study the nephrotoxic effects of (i) chloroacetaldehyde, a metabolite of the anticancer drug ifosfamide, (ii) of cobalt chloride, a potential leakage product of the cobalt-containing nanoparticles, and (iii) of valproate, a widely used antiepileptic drug. 3.Since all the latter test compounds, like many toxic compounds, negatively interact with cellular metabolic pathways, we also illustrate our biochemical toxicology approach in which we used not only enzymatic but also carbon 13 NMR measurements and mathematical modelling of metabolic pathways. 4.This original approach, which can be applied to any tissue, allows to predict the nephrotoxic effects of milligram amounts of test compounds very early during the research and development processes of drugs and chemicals. This approach, combined with the use of cells that retain their in vivo metabolic properties and, therefore, are predictive, reduces the risk, the time and cost of such processes.

Renal function and solitary kidney disease: Wilms tumour survivors versus patients with unilateral renal agenesis

AIMS

To test the hypothesis that Wilms tumour survivors (WTs) experience increased disturbance in renal function, even after prompt treatment, compared to patients with unilateral renal agenesis (URA).

METHODS

To assess the renal function of 30 WTs and 17 individuals with URA, the estimated glomerular filtration rate (eGFR) was calculated using the Schwartz and Filler formulas as well as the new Schwartz equation for chronic kidney disease. To measure kidney damage, serum levels and urine excretion of β(2)-microglobulin (B2M), cystatin C (Cys C), neutrophil gelatinase-associated lipocalin (NGAL) were tested, N-acetyl-β-glucosaminidase (NAG), and albumin urine excretion and urine sediment were examined. Blood pressure was measured.

RESULTS

No differences were found between the groups in terms of eGFR, serum Cys C, B2M and NGAL concentrations. The urine excretion of Cys C, NGAL and NAG was similar in both groups. URA patients had higher B2M excretion than WTs. Arterial hypertension was present in 7/30 (23%) WTs and 1/17 (6%) patients with URA.

CONCLUSIONS

WTs have similar eGFR to individuals with URA and are more likely to have arterial hypertension. The patients with URA have signs of tubular damage. This study demonstrates the need for nephrological monitoring of individuals with a single kidney.

Tubular nephrotoxicity induced by docetaxel in non-small-cell lung cancer patients

Renal dysfunction is a characteristic of many patients with cancer; however, a standard therapy has not been established for stage III or IV non-small-cell lung cancer (NSCLC) complicated with chronic renal failure. Docetaxel has a proven significant activity against NSCLC. This agent is predominantly eliminated by hepatobiliary extraction and is safe in patients with renal failure, including dialysis patients. Docetaxel is, thus, a therapeutic option in that patient population. Here, we report acute tubular nephrotoxicity secondary to docetaxel in NSCLC patients, even in patients with normal renal function. Little is known about tubular nephrotoxicity induced by docetaxel; however, oncologists should be aware of its possibility.

Glomerular filtration rate and prevalence of chronic kidney disease in Wilms' tumour survivors

Glomerular filtration rate (GFR) was evaluated in 32 Wilms' tumour survivors (WTs) in a cross-sectional study using 99 Tc-diethylene triamine pentaacetic acid (99 Tc-DTPA) clearance, the Schwartz formula, the new Schwartz equation for chronic kidney disease (CKD), cystatin C serum concentration and the Filler formula. Kidney damage was established by beta-2-microglobulin (B-2-M) and albumin urine excretion, urine sediment and ultrasound examination. Blood pressure was measured. No differences were found between the mean GFR in 99 Tc-DTPA and the new Schwartz equation for CKD (91.8 ± 11.3 vs. 94.3 ± 10.2 ml/min/1.73 m(2) [p = 0.55] respectively). No differences were observed between estimated glomerular filtration rate (eGFR) using the Schwartz formula and the Filler formula either (122.3 ± 19.9 vs. 129.8 ± 23.9 ml/min/1.73 m(2) [p = 0.28] respectively). Increased urine albumin and B-2-M excretion, which are signs of kidney damage, were found in 7 (22%) and 3 (9.4%) WTs respectively. Ultrasound signs of kidney damage were found in 14 patients (43%). Five patients (15.6%) had more than one sign of kidney damage. Eighteen individuals (56.25%) had CKD stage I (10 with signs of kidney damage; 8 without). Fourteen individuals (43.75%) had CKD stage II (6 with signs of kidney damage; 8 without). The new Schwartz equation for CKD better estimated GFR in comparison to the Schwartz formula and the Filler formula. Furthermore, the WT survivors had signs of kidney damage despite the fact that GFR was not decreased below 90 ml/min/1.73 m(2) with 99 Tc- DTPA.

Nephrotoxicity of cancer treatment in children

Chronic renal impairment in children with cancer may be caused by the malignant process itself or result from adverse effects of treatment including cytotoxic drugs, radiotherapy, surgery or supportive treatment. Although severe renal chronic disease is uncommon, occurring in only 0.8% of long-term survivors of childhood cancer, 1.9% of all cases of established renal failure are due to malignancy and 0.8% to drug nephrotoxicity. The relative risk of severe renal chronic disease (compared with siblings) is 8.1, and that of renal failure or the need for dialysis is 8.9. The cytotoxic drugs most likely to cause important chronic nephrotoxicity are ifosfamide and cisplatin, both of which are used widely in many solid tumors and may cause chronic glomerular and/or renal tubular toxicity in 30–60% of treated children. Significant renal toxicity is less frequent with other chemotherapeutic drugs, but may result from treatment with carboplatin, methotrexate and nitrosoureas. Other cytotoxic drugs occasionally cause specific patterns of glomerular or tubular toxicity in children. Partial or unilateral nephrectomy leads to hypertrophy and hyperfiltration of the remaining renal tissue, and may result in microalbuminuria, hypertension and in rare cases, chronic renal impairment. Radiotherapy to a field including renal tissue may cause late onset chronic renal damage, manifest by hematuria, proteinuria, hypertension and anemia, sometimes progressing to chronic renal failure. Chronic nephrotoxicity is also common in survivors of hemopoietic stem cell transplantation, and is often multifactorial with contributions from prior chemotherapy, total body irradiation, immunosuppressive drugs and transplant complications, such as infection or hemorrhage. Patients at risk of renal damage should be monitored regularly with a defined surveillance protocol to enable timely management. General measures often employed to prevent or reduce nephrotoxicity include the use of intravenous hydration during drug administration and avoidance of known risk factors, such as high drug doses. Although numerous potentially nephroprotective drugs have been suggested and investigated, none have yet been introduced into clinical use in children due to the lack of proven efficacy. Improved understanding of the pathogenesis of nephrotoxicity is necessary to reduce the frequency and severity of this potentially serious complication of treatment in children with cancer.

Cystatin C and parenchymal thickness/kidney length ratio in Wilms tumor survivors

BACKGROUND

This study presents a clinical, biochemical, and sonographic evaluation of single kidneys in Wilms tumor survivors.

PROCEDURE

The function of single kidneys in 26 Wilms tumor survivors (mean age, 11.17 years; mean follow-up, 7.09 years) was evaluated using cystatin C (CysC) levels and compared to serum creatinine concentration and glomerular filtration rate (eGFR), the latter of which was estimated by the Schwartz formula. The length of the kidney, the resistance index (RI) of the renal vessels, and the parenchymal thickness/kidney length ratio (PT/KL) were evaluated by sonographic examination.

RESULTS

Group A (n = 15) consisted of children with normal CysC levels, and group B (n = 11) consisted of children with CysC over 0.95 mg/L. No differences were observed between the groups in creatinine concentration, age, follow-up evaluation, age at the time of diagnosis, or kidney size. Children with elevated CysC had statistically lower eGFR (P = 0.02) and PT/KL (P = 0.0065). The correlation rate between CysC and PT/KL in all children was -0.38. Kidney hypertrophy was observed in 23 children and was correlated with CysC (group A, R = 0.46; group B, R = 0.4; P < 0.05). RI was normal in all individuals.

CONCLUSIONS

CysC levels may be elevated in people with normal GFR. Hypertrophy of a single kidney increases with deteriorating kidney function. PT/KL should be verified in future studies as a sonographic marker of kidney impairment.

Late effects on renal glomerular and tubular function in childhood cancer survivors

BACKGROUND

Late nephrotoxicity among childhood cancer survivors is poorly documented.

METHODS

We investigated 115 patients and 86 controls assessing serum cystatin C concentration (CysC), urinary N-acetyl-beta-D-glucosaminidase activity (NAG), and microalbuminuria. Proteinuria was quantified and electrophoresis performed. Polymorphism of the angiotensin convertase enzyme (ACE) gene was determined by genomic PCR.

RESULTS

CysC was elevated in Wilms tumor (WT) patients. Gross proteinuria was observed in 30 patients including three patients with progressive proteinuria who improved on ACE-inhibitor treatment. Neither patients with proteinuria nor the entire study population differed from controls with respect to ACE polymorphism. Pathologically elevated urinary NAG was noted in 38% of leukemia/lymphoma, 54% of solid tumor, 20% of WT survivors. A similar distribution of pathological microalbuminuria was found.

CONCLUSIONS

Mild-to-moderate subclinical glomerular and tubular damage can be identified in many childhood cancer survivors. However, most patients experience some spontaneous recovery from acute nephrotoxicity.

Chronic ifosfamide nephrotoxicity in children

Nephrotoxicity is a frequent complication of treatment with ifosfamide in children. Although renal damage may be acute and reversible, chronic toxicity may develop with potentially serious consequences. Chronic nephrotoxicity due to ifosfamide may lead to a wide variety of subclinical and clinical manifestations. Proximal tubular dysfunction is the commonest presentation, and may lead to a Fanconi syndrome, including hypophosphataemic rickets and proximal renal tubular acidosis. Glomerular impairment is also common, whilst distal tubular impairment has been described but is relatively rare. Although full reversibility has been described occasionally, there is no information about the very long-term outcome of chronic ifosfamide nephrotoxicity. We studied a cohort of 12 children 1 and 10 years after completion of ifosfamide treatment. There was no statistically significant change in either glomerular or tubular toxicity in the group as a whole over this time period. However, marked improvements were seen in some aspects of toxicity in some patients, and deterioration was observed in others. We concluded that considerable nephrotoxicity is still present 10 years after completion of ifosfamide treatment, but that the outcome varies between individual patients. Although several risk factors for the development of chronic nephrotoxicity have been described, total ifosfamide dose, patient age at treatment, previous or concurrent cisplatin treatment, and unilateral nephrectomy are the most important. Nevertheless, it remains difficult to predict the occurrence of this toxicity with confidence. The pathogenesis of ifosfamide nephrotoxicity is poorly understood. There is an urgent need for the development and clinical investigation of nephroprotective strategies.

Human kidney tubules detoxify chloroacetaldehyde, a presumed nephrotoxic metabolite of ifosfamide

The nephrotoxic effects of the antineoplastic drug ifosfamide have been attributed to its hepatic metabolite chloroacetaldehyde. The effects of chloroacetaldehyde on isolated human kidney cortex tubules metabolizing lactate (a physiologic substrate in human kidneys) were investigated. At concentrations of > or =0.5 mM, chloroacetaldehyde was toxic to the human kidney tubules, as demonstrated by a dramatic decrease in cellular ATP levels and a large increase in lactate dehydrogenase release; chloroacetaldehyde also stimulated pyruvate accumulation and inhibited lactate removal and glucose synthesis. These effects, which were associated with incomplete disappearance of chloroacetaldehyde and extensive depletion of the cellular CoA, acetyl-CoA, and glutathione contents, were prevented by the addition of thiol-protecting drugs (mesna and amifostine). Human kidney tubules were demonstrated to metabolize chloroacetaldehyde at high rates, presumably via aldehyde dehydrogenase, which is very active in human kidneys. Carbon-13 nuclear magnetic resonance spectroscopy measurements indicated that human kidney tubules converted [2-(13)C]chloroacetaldehyde to [2-(13)C]chloroacetate, the further metabolism of which was very limited. At equimolar concentrations, chloroacetate was much less toxic than chloroacetaldehyde, indicating that chloroacetate synthesis from chloroacetaldehyde by human kidney tubules represents a detoxification mechanism that could play a role in vivo in preventing or limiting the nephrotoxic effects observed during ifosfamide therapy.

Anticancer drug-induced kidney disorders

Nephrotoxicity is an inherent adverse effect of certain anticancer drugs. Renal dysfunction can be categorised as prerenal uraemia, intrinsic damage or postrenal uraemia according to the underlying pathophysiological process. Renal hypoperfusion promulgates prerenal uraemia. Intrinsic renal damage results from prolonged hypoperfusion, exposure to exogenous or endogenous nephrotoxins, renotubular precipitation of xenobiotics or endogenous compounds, renovascular obstruction, glomerular disease, renal microvascular damage or disease, and tubulointerstitial damage or disease. Postrenal uraemia is a consequence of clinically significant urinary tract obstruction. Clinical signs of nephrotoxicity and methods used to assess renal function are discussed. Mechanisms of chemotherapy-induced renal dysfunction generally include damage to vasculature or structures of the kidneys, haemolytic uraemic syndrome and prerenal perfusion deficits. Patients with cancer are frequently at risk of renal impairment secondary to disease-related and iatrogenic causes. This article reviews the incidence, presentation, prevention and management of anticancer drug-induced renal dysfunction. Dose-related nephrotoxicity subsequent to administration of certain chloroethylnitrosourea compounds (carmustine, semustine and streptozocin) is commonly heralded by increased serum creatinine levels, uraemia and proteinuria. Additional signs of streptozocin-induced nephrotoxicity include hypophosphataemia, hypokalaemia, hypouricaemia, renal tubular acidosis, glucosuria, aceturia and aminoaciduria. Cisplatin and carboplatin cause dose-related renal dysfunction. In addition to increased serum creatinine levels and uraemia, electrolyte abnormalities, such as hypomagnesaemia and hypokalaemia, are commonly reported adverse effects. Rarely, cisplatin has been implicated as the underlying cause of haemolytic uraemic syndrome. Pharmaceutical antidotes to cisplatin-induced nephrotoxicity include amifostine, sodium thiosulfate and diethyldithiocarbamate. Dose- and age-related proximal tubular damage is an adverse effect of ifosfamide. In addition to renal wasting of electrolytes, glucose and amino acids, Fanconi syndrome, rickets and osteomalacia have occurred with ifosfamide treatment. High dose azacitidine causes renal dysfunction manifested by tubular acidosis, polyuria and increased urinary excretion of electrolytes, glucose and amino acids. Haemolytic uraemia is a rare adverse effect of gemcitabine. Methotrexate can cause increased serum creatinine levels, uraemia and haematuria. Acute renal failure is reported following administration of high dose methotrexate. Urinary alkalisation and hydration confer protection against methotrexate-induced renal dysfunction. Dose-related nephrotoxicity, including acute renal failure, are reported subsequent to treatment with pentostatin and diaziquone. Acute renal failure is a rare adverse effect of treatment with interferon-alpha. Haemolytic uraemic syndrome occurs with mitomycin administration. A mortality rate of 50 to 100% is reported in patients developing mitomycin-induced haemolytic uraemic syndrome. Capillary leak syndrome occurring with aldesleukin therapy can cause renal dysfunction. Infusion-related hypotension during infusion of high dose carmustine can precipitate renal dysfunction.

Development of ifosfamide-induced nephrotoxicity: prospective follow-up in 75 patients

PURPOSE

This study was performed to describe prospectively the development and prognosis of severe ifosfamide-induced nephrotoxicity and to define the period of recommended renal follow-up after ifosfamide chemotherapy.

PATIENTS AND METHODS

Renal function was followed in 75 patients after cessation of chemotherapy starting within the first year off therapy; median follow-up time was 31 months. The glomerular filtration rate was estimated by using the Schwartz formula. Proximal tubular transport capacities were evaluated for amino acids, phosphate, sodium, and glucose. In addition, serum bicarbonate level and alkaline phosphatase were measured.

RESULTS

Five patients developed renal Fanconi syndrome during follow-up, and another seven patients developed a generalized subclinical tubulopathy. The latter condition always preceded Fanconi syndrome. Severe impairment of amino acid and phosphate reabsorption was seen in 28% and 17.3% of patients, respectively. Reductions in amino acid reabsorption preceded impairment of phosphate reabsorption. In patients with early impairment of phosphate reabsorption, renal prognosis was poor, whereas normal or only mildly impaired amino acid handling virtually excluded progressive tubular damage.

CONCLUSIONS

Ifosfamide-induced renal tubular damage is a potentially progressive disease. Along with measurement of phosphate reabsorption, additional assessment of tubular amino acid handling is suggested, because it allows early discrimination of poor from favorable renal outcomes.

Renal function following combination chemotherapy with ifosfamide and cisplatin in patients with osteogenic sarcoma

BACKGROUND

Ifosfamide and cisplatin are active agents that are currently used in the treatment of osteosarcoma. Nephrotoxicity has been reported following their use in combination and alone. This study evaluates renal function in children and adolescents (median age 16 years) at least 3 months following completion of a chemotherapy regimen which included 54 g/m2 ifosfamide, 360 mg/m2 cisplatin, doxorubicin, and high-dose methotrexate.

PROCEDURE

Mean glomerular filtration rate (GFR) was determined by inulin or iothalamate clearance; proximal tubular function was evaluated by measuring fractional excretion of glucose (FEglu), tubular maximum phosphate reabsorption per GFR (TMP/GFR), FE of urate, and 24-hour amino acid excretion. Distal tubular function was evaluated by 24-hour urinary calcium, FE of magnesium, and urinary osmolality after water deprivation. Twenty-four-hour urinary protein excretion was measured.

RESULTS

The mean GFR was 97 ml/min/1.73 m2. Although 10 of 24 patients had GFRs lower than normal, the lowest value was only 22% below the lower limit of normal and would not account for any clinical compromise. Proximal tubular function evaluation revealed normal FEglu, normal mean TMP/GFR values, and high FE of urate (1 5.7%). Two of twenty-four patients were shown to have mild generalized aminoaciduria. Distal tubular function evaluation showed normal 24-hour urinary calcium levels (mean 3.4 mg/kg) and FE of magnesium as well as normal urinary osmolality. Twenty-four-hour urinary protein excretion was normal in all patients.

CONCLUSIONS

The lack of clinically significant renal abnormalities observed in patients who received combination chemotherapy with ifosfamide and cisplatin for osteosarcoma is encouraging for future osteosarcoma protocol development.

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.

Ifosfamide nephrotoxicity in paediatric cancer patients

Ifosfamide is an alkylating agent which has been incorporated into frontline therapy for a number of malignant paediatric tumours. Recent data appears to suggest that tubular dysfunction may result from incorporation of this drug into chemotherapy schedules and that toxicity may be dose related. A detailed investigation of renal function was performed in a group of patients, ranging in age from 8 months to 15.9 years (median 8.6 years) with rhabdomyosarcoma (n = 11) and Ewing's sarcoma (n = 9) who were currently receiving (n = 4) or had completed ifosfamide (n = 16) therapy a mean of 16 months at the time of study. All but one patient demonstrated some degree of renal dysfunction and toxicity did not necessarily appear to be dose related. Implications for incorporation of this agent into future schedules for childhood sarcomas, which can expect to cure more than 60% of such children, must be addressed. The importance of ongoing monitoring is emphasised.

Ifosfamide-induced renal tubular defect

We describe 2 cases of proximal tubular defects induced by the administration of ifosfamide at a dosage of 6 g/m2/course over 2 days in children with a diagnosis of malignant mesenchymal tumors. This adverse effect could be minimized dividing dosage of the drug. However at present it is not clear if divided doses are completely safe.

Renal function in children and adolescents following 72 g/m2 of ifosfamide

A detailed analysis of the renal function of 18 children and adolescents aged 7-20 years (median, 16 years) was performed at least 3 months following the completion of a non-platinum-containing chemotherapy regimen with a total dose of 72 g/m2 of ifosfamide. Ifosfamide had been given as a 1-h infusion of 1.8 g/m2 daily for 5 days at 5- to 6-week intervals along with mesna uroprotection. The mean glomerular filtration rate (GFR) as determined by inulin clearance was 100 ml/min/1.73 m2. Although 6 of 18 patients had GFRs below normal, the lowest was only 18% less than the lower limit of normal and would not account for any clinical compromise. The renal plasma flow and filtration fraction were normal. Proximal tubular function evaluation revealed normal fractional excretion (FE) of glucose; normal mean tubular maximum phosphate reabsorption per GFR (TMP)/GFR values; high FE of urate (17%); and mild, generalized aminoaciduria in 6 of the 18 patients. Distal tubular function evaluation showed normal 24-h urinary calcium levels and FE of magnesium as well as normal urinary osmolality after water deprivation. Two patients had mild proteinuria. The findings in this study are encouraging in terms of the lack of clinically significant renal abnormalities observed in patients who had received a cumulative dose of 72 g/m2 of ifosfamide.

Determination of the urinary excretion of ifosfamide and its phosphorated metabolites by phosphorus-31 nuclear magnetic resonance spectroscopy

Phosphorus-31 nuclear magnetic resonance spectroscopy was used to analyze urine samples obtained from patients treated with ifosfamide (IF). This technique allows the individual assay of all phosphorated metabolites of IF in a single analysis without the need for prior extraction. In addition to the classic IF metabolites 2-dechloroethylifosfamide (2DEC1IF), 3-dechloroethylifosfamide (3DEC1IF), carboxyifosfamide (CARBOXYIF), and isophosphoramide mustard (IPM), several signals corresponding to unknown phosphorated compounds were observed. Four of them were identified: one is alcoifosfamide (ALCOIF), two come from the degradation of 2,3-didechloroethylifosfamide (2,3-DEC1IF), and one results from the decomposition of 2DEC1IF. The total cumulative drug excretion as measured over 24 h in nine patients was 51% of the injected IF dose; 18% of the dose was recovered as unchanged IF. The major urinary metabolites were the dechloroethylated compounds, with 3DEC1IF excretion (11% of the injected dose) always being superior to 2DEC1IF elimination (4% of the injected dose). Degradation compounds of 2DEC1IF and 2,3DEC1IF represented 0.4% of the injected dose. The metabolites of the dechloroethylation pathway always predominated over those of the activation pathway (CARBOXYIF, ALCOIF, and IPM, representing 3%, 0.8%, and 0.2% of the injected dose, respectively). In all, 14% of the injected dose was excreted as unknown phosphorated compounds. The interpatient variation in levels of IF metabolites was obvious and involved all of the metabolites. Renal excretion was not complete at 24 h, since 11% of the injected dose was recovered in the 24- to 48-h urine samples.

Uroepithelial and nephrotubular toxicity in patients receiving ifosfamide/mesna: measurement of urinary N-acetyl-beta-D-glucosaminidase and beta-2-microglobulin

The effect of three ifosfamide/mesna regimens on urinary N-acetyl-beta-D-glucosaminidase (NAG) activity and beta-2-microglobulin (beta 2 M) was studied. All regimens produced significant increases in these urinary proteins, indicating nephrotubular damage. In regimen A (n = 15), plasma nitrobenzylpyridine (NBP) alkylating activity area under the curve (AUC) on day 1 correlated with the percentage increase above baseline of maximum urinary NAG activity (r2 = 0.538, P = 0.0022) and maximum beta 2 M concentration (r2 = 0.413, P = 0.0097). In regimen B (n = 5), plasma NBP alkylating activity AUC correlated with the percentage increase above baseline of maximum NAG activity (r2 = 0.843, P = 0.03) and beta 2 M (r2 = 0.78, P = 0.046). In these two regimens the renal exposure to ifosfamide metabolites correlated with the increases in urinary NAG and beta 2 M. The relation of these urinary protein abnormalities to longer term effects on renal function with different ifosfamide/mesna schedules requires further study.

Progressive renal toxicity due to ifosfamide

A prospective and follow up study of renal tubular and glomerular function in 11 children receiving ifosfamide treatment was conducted. Each child received between four and 14 courses of ifosfamide, given as a continuous infusion of 3 g/m2 over 24 hours for two or three days. Evidence of renal toxicity was seen in all patients. There was a treatment related rise in urinary tubular markers (N-acetyl-glucosaminidase and alpha 1 microglobulin). Recovery was limited, so that by the fourth course of treatment all values remained abnormal. There was an associated treatment related reduction in plasma phosphate concentration. Urinary albumin also showed a treatment related rise, but with fewer abnormal values. Electrophoresis was used to confirm tubular or glomerular patterns. Glomerular toxicity was less severe and occurred in fewer patients. The follow up study showed persistence of tubular damage in all seven patients examined, and there was evidence of glomerular damage in five of the seven children. Children receiving ifosfamide need to be carefully monitored for renal toxicity both during treatment and at follow up.

Dosing and side-effects of ifosfamide plus mesna

In clinical practice and in most ongoing studies in adult and pediatric tumours, daily short-time infusions of ifosfamide (IFO) on 2-5 consecutive days with cycle doses between 6 g/m2 and 12 g/m2 are used at present. The continuous i.v. infusion of IFO/mesna over 1-5 days is still experimental. Since mesna prevents IFO-induced urotoxicity, the IFO dose could be increased to 16 g/m2 per cycle. As the dose and schedules of IFO/mesna were increased and varied, CNS and renal toxicity became more evident. CNS toxicity seems not to be dependent on i.v., but on oral dosing of IFO. Renal dysfunction and previous administration of cisplatinum predispose for CNS toxicity. The incidence or severity of CNS toxicity does not increase with subsequent courses of IFO i.v. The nephrotoxicity of IFO is dependent on IFO dose, diuresis, mesna dose and whether there has been previous cisplatinum and seems to involve preferentially the tubulus system, leading to 25 cases of Fanconi renal syndrome as published in 1988-1990. Fanconi's syndrome depends on the cumulative IFO dose, the previous administration of nephrotoxic drugs such as cisplatinum and the age of the children. Studies are continuing to determine the least nephrotoxic dose and schedule of IFO plus mesna. Leucopenia and thrombopenia are well-known dose-dependent side-effects of IFO, with similar incidence after i.v. short-time and continuous infusion.

Urinary excretion of the enantiomers of ifosfamide and its inactive metabolites in children

The precondition for the antineoplastic effect of ifosfamide (ifo) is the oxidation of the oxazaphosphorine ring system, which contains a chiral centre at the phosphorous atom. This "ring oxidation" leads to the formation of alkylating mustard via several steps. A second metabolic pathway produces the cytostatically inactive metabolites 2- and 3-dechloroethyl-ifosfamide (2-d- and 3-d-ifo). The urinary excretion of the optical isomers of unmetabolised ifo and of 2- and 3-d-ifo, which represents the amount of ifo that has not been activated, was investigated by capillary gas chromatography for 18 treatment cycles in 14 children on various therapeutic schedules. The total cumulative excretion in 12 completely sampled cycles ranged from 27% to 50% of the ifo dose. Between 14% and 34% of the dose could be detected as ifo; 9% to 29%, as 3-d-ifo; and 2% to 8%, as 2-d-ifo. At 24 h after the end of therapy, excretion was nearly complete. Without exception, slightly more R-ifo (53%-61%) than S-ifo was excreted. S-2-d-ifo (50%-73%) was the main 2-d-metabolite. S-3-d-ifo (deriving from R-ifo) predominated in 6 of 14 children and R-3-d-ifo, in 8. Enantiomer-specific excretion increased after the end of infusion (up to 73% for R-ifo and 27% for S-ifo). We demonstrated stereospecific metabolism of ifo in children, with two different patterns of side-chain oxidation being observed. There was no evidence of important stereospecific ring oxidation in most children. A benefit should not be expected from the therapeutic application of pure enantiomers.