Renal effects of cyclosporin A in children treated for idiopathic nephrotic syndrome

Little data have been published on tubular renal function during cyclosporin A treatment in children without transplants. We studied 12 young subjects (mean age 10 years) with steroid-responsive idiopathic nephrotic syndrome and with signs of steroid toxicity. After achieving remission with prednisone 60 mg/m2, 8 children started cyclosporin A therapy (6 mg/kg/day) (group A) and 4 children were given cyclophosphamide 2.5 mg/kg/day (group B). The latter were considered as controls together with 10 other children with idiopathic nephrotic syndrome in complete remission and off therapy (group C). We monitored creatinine clearance and tubular handling of beta 2-microglobulin, sodium, phosphorus and uric acid for one year. Cyclosporin A induced a decrease in creatinine clearance with a decrease in fractional excretion of beta 2-microglobulin; sodium excretion was similar in the two treated groups and a transient decrease in fractional excretion of uric acid was seen only in patients receiving cyclosporin A. Both groups showed an increased renal threshold phosphate concentration. Our results suggest that in children, cyclosporin A therapy induces a decrease in glomerular filtration rate associated with increased reabsorption activity of proximal tubular cells.

Sodium excretion and hyperfiltration during glucose infusion in man

The relations between renal hemodynamics (Inutest, CPAH) and sodium excretion were studied in 7 nondiabetics in whom a similar expansion was induced (1) with a 3-hour 5% glucose infusion and (2) with a 0.9% saline load. With both infusions the body weight increased, hematocrit fell, and the plasma renin activity was suppressed. During glucose infusion, blood glucose rose from 3.9 mmol/l to a plateau of around 13 mmol/l; glycosuria was absent during the 1st h, then appeared and stabilized during the following 2h. Glucose infusion caused a progressive increase in glomerular filtration rate and in renal blood flow in both absence and presence of glycosuria, without significant changes in sodium excretion despite volume expansion and increase of filtered sodium load. When saline was infused, there was a sustained increase of fractional sodium excretion, and no hemodynamic modifications were observed. We suggest that a primary glucose-induced metabolic stimulation of sodium reabsorption may play a role in the genesis of glucose-induced hyperfiltration.

Lack of glomerular hemodynamic stimulation after infusion of branched-chain amino acids

Renal hemodynamics (Inutest. CPAH) were studied in five adult volunteers infused on separate occasions with branched-chain amino acids (BCAA), a mixture of nonessential and essential amino acids of the same volume, osmolality and nitrogen content, and 0.9% saline solution. BCAA infusion caused moderate renal vasoconstriction, a slight increase of GFR and a progressive rise of the filtration fraction (FF), whereas the amino acids mixture induced a significantly higher increase of GFR and a state of renal vasodilatation without altering the FF. The volume expansion with 0.9% saline did not cause any notable hemodynamic modification except for reduced FF. This study demonstrates that whereas a state of hyperfiltration and hyperemia is specifically induced by an amino acid mixture independently of volume expansion and osmolar load, the administration of BCAA provides nitrogen without renal hemodynamic stimulation.

Proximal tubular function and hyperfiltration during amino acid infusion in man

The relations between renal hemodynamics (Inutest, CPAH) and sodium segmental handling (sodium distal delivery, distal reabsorption, and fractional excretion) were studied in 9 healthy adults infused with an isotonic amino acid solution and in 6 subjects infused with 0.9% saline for 3 h at 0.2 ml/min/kg. During all tests maximal water diuresis was induced and maintained to effect analysis of sodium segmental transport. Both types of infusion produced a similar expansion of extracellular volume (weight increase, hematocrit fall, suppressed plasma renin activity and plasma aldosterone). The amino acid infusion increased the glomerular filtration rate (GFR) and renal blood flow without modifying the filtration fraction. With saline no hemodynamic modifications were observed. The expansion with saline depressed proximal and distal sodium reabsorption whereas during amino acid infusion sodium distal delivery was unaltered and the significantly increased sodium fractional excretion was sustained only by depressed distal reabsorption. Therefore, in parallel with the GFR increase, closely dependent on renal vasodilatation, the well-known stimulation of sodium cotransport by amino acids is able to antagonize the effects of expansion on the proximal sodium reabsorption. An explanation of glomerular hyperfiltration based on a primary metabolic stimulation of the proximal tubular function is suggested.

Persistent tubular resistance to aldosterone in infants with congenital hydronephrosis corrected neonatally

Renal function of 18 infants who had undergone surgery in the neonatal period because of severe congenital hydronephrosis was followed up for 5 to 36 months (mean +/- SD 21 +/- 10 months). In all cases the diagnosis was made prenatally by sonography and confirmed at birth by intravenous urography. Creatinine clearance developed normally in all the children. Eight had a reduction in maximal urinary concentrating ability after intranasal DDAVP; this defect was transient and resolved after 4 to 5 months in all but one child, in whom it persisted. However, other tubular abnormalities were present. Throughout the observation period, patient serum potassium concentrations were significantly higher than normal, paralleled by a significant increase in plasma aldosterone concentration but with normal excretion fraction of sodium and potassium. There were no disturbances of acid-base balance. These findings may be accounted for by a persistent partial reduced sensitivity of the distal tubule to the action of aldosterone despite normal renal function. This alteration is usually mild, but may constitute a persistent metabolic risk despite successful surgical intervention.

Early childhood hyperkalemia: variety of pseudohypoaldosteronism

Fractional excretion of electrolytes, renal acidification capacity and the renin-aldosterone system have been studied in 5 non-azotemic children, 19-25 months old, with mineralocorticoid resistant hyperkalemia, discovered in the first month of life. Although fractional potassium excretion was similar in patients and in a group of control healthy children (13.8 +/- 5.2% vs. 8.7 +/- 6.4%) it was inappropriately low in the patients for their higher potassium concentration. Fractional sodium excretion was significantly increased in the patients (1.6 +/- 0.3% vs. 0.67 +/- 0.4, p less than 0.02). Normal net acid and ammonium excretion and intact ability to lower urinary pH during acid loading were observed in all patients. Mean values for plasma aldosterone (37.0 +/- 9.1 vs. 13.9 +/- 11.2 ng/dl), plasma renin activity (12.5 +/- 3.9 vs. 8 +/- 2.8 ng/ml/h) and plasma aldosterone/plasma potassium ratio (7.11 +/- 1.5 vs. 3.08 +/- 1.7) were higher in the patients than in the control subjects (all p less than 0.001). These data support the hypothesis that a partial lack of response of the renal tubule to endogenous mineralocorticoids was present in the patients. This type of pseudohypoaldosteronism is less severe than that described for the classic form and for early childhood renal acidosis.

Renal function in cystic fibrosis

The effect of saline extracellular volume expansion (4 ml/min/10 kg b.w. X 60 min) on renal function has been studied in patients with cystic fibrosis (CF) and in normal age-matched controls. Basal values for glomerular filtration rate (GFR), renal plasma flow (RPF), tubular sodium and chloride (Na, Cl) handling were similar in both groups. Saline expansion resulted in an increase in GFR and RPF in the CF patients: 127 +/- 18 ml/min/1.73 sqm BSA to 166 +/- 5; p less than 0.001, but not in the control group: 112 +/- 10 to 120 +/- 20. These hemodynamic changes were associated with increased proximal tubular reabsorption of NaCl in the CF patients whereas controls had reduced NaCl reabsorption. Renin and aldosterone levels suggested that increased NaCl reabsorption in CF patients was not secondary to chronic extracellular volume contraction or salt loss. These results support the hypothesis that the renal tubule is involved in the generalised electrolyte transport disorder exhibited in other epithelial structures. This study also indicated that the regulation of renal hemodynamics is altered in CF. The relationship between the disorder of proximal tubular salt handling and changes in renal hemodynamics is not known, but the observed changes imply a tubulo-glomerular feedback mechanism.

Follow-up study of enzymuria and beta 2 microglobulinuria during cis-platinum treatment

Twenty patients with epithelian ovarian cancer treated with DDP (cis-diammine-dichloroplatinum II) 50 mg/m2 were followed for 24 weeks in order to assess the nephrotoxicity of the drug. Ten patients received the total dose in one day with heavy osmotic hydration (Group A), and for the other 10 the dose was subdivided over 3 consecutive days (Group B). The renal tubular toxicity of DDP treatment was evaluated over a total of 120 courses. After the first DDP administration, there was a prompt, reversable and dose-dependent increase in the urinary excretion of beta 2 microglobulin with no difference between the two groups: Group A from 405 to 990 and Group B from 109 to 585 ng/mg creatinine. An increase always occurred during subsequent courses, but it was significantly lower in Group B after the sixth course, from 125 to 331 ng/mg creatinine. A similar pattern was found for the urinary excretion of N-acetyl-glucosaminidase (NAG), a lysosomal enzyme of tubular origin. The percentage fraction of urinary sodium excretion (FeNa%) increased after each dose of DDP; Group A from 0.82 to 2.30 and Group B from 0.68 to 2.53. This effect was reversible and it occurred to the same extent during the subsequent courses. There was no impairment of the glomerular filtration rate. Thus, enzymuria and beta 2 microglobulin excretion are a sensitive tool to reveal minor tubular damage. Their use to predict serious renal dysfunction in longitudinal studies, however, seems questionable.

Monitoring of amikacin in the neonate

The purpose of this study was to analyze the role of gestational and postnatal age and of clinical conditions [e.g., respiratory distress syndrome (RDS)] on serum concentrations of amikacin in neonates treated according to commonly recommended dose schedules. Thirty-nine neonates (28.5-42 weeks of gestational age) were treated with the aminoglycoside at a mean dose of 7.2 mg/kg every 12 h for an average period of 6.5 days, and serum levels were monitored throughout treatment. Both gestational and postnatal age influenced amikacin levels. During the first days of life the presence of RDS was found to be strongly associated with amikacin accumulation. Neonates with retarded intrauterine growth according to their gestational age tended to have lower amikacin trough levels in the first days of life. No correlation was found between amikacin serum levels and hematocrit. Peak concentrations of the drug did not correlate with vital or clinical data, probably because of the variability in drug absorption from the intramuscular injection site. These data are discussed in light of the development of renal function and changes in body fluid compartments occurring in the preterm and term neonates during the first weeks of life.

Comparative pharmacokinetics of aminoglycoside antibiotics in guinea pigs

The pharmacokinetics of netilmicin, gentamicin, and tobramycin in plasma and in perilymph of guinea pigs were studied after a single intravenous injection of 40 mg/kg. Detailed pharmacokinetic analysis of the plasma drug concentration-time data up to 36 h after the intravenous dose revealed that the pharmacokinetics of the aminoglycoside antibiotics can be best described as a three-compartment open model. The disposition half-lives (t1/2) in plasma of the three antibiotics were comparable and within the following ranges: t1/2 alpha of 0.09 to 0.16 h; t1/2 beta of 0.88 to 1.01 h; and t1/2 gamma of 7.87 to 8.29 h. The volume of distribution in the central compartment and the total body clearance of netilmicin (294 ml/kg, 5.74 ml/min per kg) were greater than those of gentamicin (160 ml/kg, 3.40 ml/min per kg) and tobramycin (204 ml/kg, 4.63 ml/min per kg). Pharmacokinetic analysis of the perilymph drug concentration-time data indicated that all three antibiotics penetrated the perilymph readily, but netilmicin cleared from the perilymph compartment faster than gentamicin and tobramycin. The maximum perilymph drug concentrations were 4.17, 8.05, and 6.78 micrograms/ml and occurred at 1, 2, and 4 h for netilmicin, gentamicin, and tobramycin, respectively. The ratio of area under the curve of perilymph to plasma was lowest for netilmicin (0.27), followed by gentamicin (0.39) and tobramycin (0.57). These results suggest that the differences in pharmacokinetics and concentrations of netilmicin in the perilymph may account for less ototoxic liability of netilmicin compared with gentamicin and tobramycin.

Influence of intrauterine maturation on the pharmacokinetics of amikacin in the neonatal period

The effect of intrauterine maturation on amikacin disposition was studied in 29 preterm and term neonates. Mean gestational age (weeks) of the patients was 34.5 +/- 3.3 S.D. and their birth weight 1.980 +/- 920 g. After the last administration of the drug, amikacin decay was measured in plasma and urine for 100-250 h. The serum concentration versus time profiles were fitted by nonlinear regression analysis. The parameters of a 2- or 3-compartment model with elimination from the central compartment were calculated. Initial elimination T 1/2, volume of the central compartment, and steady state volume of distribution were significantly related to intrauterine maturation (respectively r = -0.76; -0.63; -0.57) whereas no significant linear correlation was found between clearance and gestational age (r = 0.19). Patients with gestational age less than 34 wk had a significantly reduced clearance when compared with the neonates with gestational age greater than 36 wk (0.78 +/- 0.17 versus 1.0 +/- 0.4 ml/h/kg, P less than 0.05). The ratio between the volumes of distribution showed that a higher amount of amikacin penetrates the peripheral compartments with increased gestational age. The renal clearance calculated in six patients averaged 66% of the total body clearance, suggesting that elimination of the drug can occur in the neonate via nonrenal routes. Analysis of the long term urinary elimination of amikacin showed that about 5% of the total amount of the drug administered in 5-8 days of treatment is retained in the organism. Although quantitatively small, this amount is relevant for the potential nephrotoxicity of the drug.