Effects of ureteral obstruction on the toxicity of cephalosporins in the rabbit kidney

Cephalosporin and carbacephem nephrotoxicity. Roles of tubular cell uptake and acylating potential

Three beta-lactams, desacetylcephaloglycin, ampicillin, and loracarbef, were studied to test a hypothesis derived from retrospective analysis of previously studied cephalosporins: that beta-lactam nephrotoxicity develops in approximate proportion to tubular cell antibiotic concentrations and lactam ring reactivities. Concentrations of each beta-lactam (and insulin) in rabbit renal cortex and serum were measured at the end of 0.5-hr infusions of 100 mg antibiotic/kg body weight and 0.5 to 0.67 hr later. Total cortical AUCs (total areas under the curve of concentration and time in renal cortex) and transported cortical AUCs (total minus insulin-space beta lactam) were calculated from these measurements. Reactivities, determined by the rate constants of lactam-ring opening at pH 10, were taken from the literature. Nephrotoxicity was quantified by grades of proximal tubular cell necrosis and by serum creatinine concentrations 2 days after infusion of 100-1500 mg/kg of the antibiotics. Desacetylcephaloglycin was slightly less nephrotoxic than cephaloglycin; the AUCs reactivities, and toxicities of these two cephalosporins fit the proposed model, particularly when allowance is made for hepatic and renal deacetylation of cephaloglycin. The very low AUCs, limited reactivity, and absence of nephrotoxicity of ampicillin also fit the model. Loracarbef had a transported AUC less than three times, and reactivity one-thirtieth, those of cefaclor, respectively. Although only at 1500 mg/kg, loracarbef was significantly more nephrotic than cefaclor. If the relativity of loracarbef with its targeted bacterial proteins, which is essentially the same as that of cefaclor, is considered instead of the base hydrolysis rate constant, than loracarbef also fits the model. By the same analysis, the comparatively high in vitro stability of other carbacephems, although pharmaceutically convenient, may not limit their nephrotoxicity.

Effects of L-carnitine on the renal tubular transport of cephaloridine

It has been demonstrated recently that cephaloridine (Cld) inhibits the tubular reabsorption of filtered carnitine (Carn) in the rabbit kidney. This interaction has suggested that the limited net cell-to-luminal fluid movement of Cld following its secretory transport across the antiluminal membrane might result from a balance of active Cld reabsorption by a Carn carrier at the brush border approximately equal to its secretion into the tubular fluid, rather than the previously proposed luminal membrane block. Studies were done to determine the effects of L-Carn, 750 mg/kg, i.v. on the tubular secretion and cortical concentrations of Cld, infused i.v. at a dose of 28 mg/kg (Carn:Cld molar ratio = 70:1). The fractional excretions of Cld during three consecutive periods of 10 min each, one before and two following the bolus infusion of Carn, were (means +/- SEM): 1.18 +/- 0.14, 1.20 +/- 0.14, and 1.16 +/- 0.11, respectively (N = 6 each; differences NS). Cortex-to-serum concentration ratios of Cld in control and Carn-treated rabbits were 10.43 +/- 0.32 and 10.16 +/- 0.86, respectively (NS). The data provide evidence against the reabsorptive transport of Cld by a Carn carrier, and do not support a model of balanced secretion and reabsorption as the cause of limited clearance despite significant secretory transport of Cld into the tubular cell.

Thienamycin nephrotoxicity. Mitochondrial injury and oxidative effects of imipenem in the rabbit kidney

The nephrotoxic cephalosoprins cephaloridine and cephaloglycin both produce mitochondrial respiratory toxicity in renal cortex. Recent work has provided evidence that this respiratory toxicity is caused by acylation and inactivation of mitochondrial anionic substrate transporters. While cephaloridine also causes significant lipid peroxidative injury in cortical mitochondria and microsomes, cephaloglycin causes little or no oxidative damage under identical conditions. The recently released thienamycin antibiotic, imipenem, like the toxic cephalosporins, produces acute proximal tubular necrosis which can be prevented completely by prior administration of probenecid. The ability of imipenem to block mitochondrial substrate uptake and respiration and produce oxidative changes has not been examined. We therefore evaluated the effects of imipenem in rabbit renal cortex on the following: (1) mitochondrial function [respiration with and uptake of succinate, and uptake of ADP]; and (2) evidence of oxidative change [depletion of reduced glutathione (GSH), production of oxidized glutathione (GSSG), and production of lipid peroxidative injury, as reflected in microsomal conjugated dienes (CDs)]. The mitochondrial effects of 300 mg/kg body wt of imipenem, given i.v. 1 and 2 hr before killing the animals, were comparable to those of the nephrotoxic cephalosporins. There was significant reduction of respiration with, and unidirectional uptake of, succinate at both times, while mitochondrial ADP transport was comparatively unaffected. Imipenem also depleted GSH and increased GSSG and CDs at 1 hr. These effects, however, were considerably smaller than those of a comparably nephrotoxic dose of cephaloridine, and this evidence of oxidative stress had resolved by 2 hr. We conclude that imipenem and the nephrotoxic cephalosporins have similar effects on mitochondrial substrate uptake and respiration, but differ significantly in their production of oxidative injury.

Oxidative and mitochondrial toxic effects of cephalosporin antibiotics in the kidney. A comparative study of cephaloridine and cephaloglycin

Cephaloridine and cephaloglycin are the two most nephrotoxic cephalosporins released for human use. Cephaloridine has been shown to produce both oxidative and mitochondrial respiratory injury in renal cortex in patterns of dose (or concentration) and time that are consistent with pathogenicity. Cephaloglycin also produces respiratory toxicity, and recent studies have provided evidence that this injury results from an inactivation of mitochondrial anionic substrate transporters. The abilities of cephaloglycin to produce oxidative changes and cephaloridine to block mitochondrial substrate uptake have not been examined yet. We therefore compared these two cephalosporins with one another and with cephalexin, which is not nephrotoxic, in the production of the following: (1) several components of oxidative stress or damage [depletion of reduced glutathione (GSH) and production of oxidized glutathione (GSSG) in renal cortex, inhibition of glutathione reductase in vitro, and production of the lipid peroxidation products malondialdehyde (MDA) and conjugated dienes (CDs) in renal cortex]; and (2) renal cortical mitochondrial toxicity [to both respiration with, and the transport of, succinate]. Cephaloridine depleted GSH and elevated GSSG in renal cortex, inhibited glutathione reductase, and increased both MDA in whole cortex and CDs in cortical microsomes and mitochondria. While cephaloglycin depleted GSH at least as much as did cephaloridine, it produced one-fifth as much GSSG and had little or no effect on glutathione reductase activity or on cortical MDA or microsomal CDs; cephaloglycin caused a transient small increase of mitochondrial CDs. Cephalexin produced no oxidative changes except for a slight increase of mitochondrial CDs comparable to that produced by cephaloglycin. Both cephaloridine and cephaloglycin, but not cephalexin, decreased the unidirectional uptake of, and respiration with, succinate in cortical mitochondria. We conclude that cephaloridine and cephaloglycin are both toxic to mitochondrial substrate uptake and respiration, but differ significantly in their generation of products of oxidation.

Nephrotoxic drugs

The nephrotoxic effects of cyclosporine, aminoglycoside antibiotics, cisplatin, amphotericin B, beta-lactam antibiotics and indomethacin are reviewed. These drugs were chosen because they are among the most frequent causes of renal injury in children. In addition, their nephrotoxicity is caused by different mechanisms. Several generalizations can be made, however. First, agents which cause tubular damage tend to be synergistic in their toxic effects. This synergism is seen when several nephrotoxic drugs are given simultaneously. In addition, the use of a nephrotoxic agent in a patient with pre-existing renal disease can result in severe tubular injury. Second, serum levels of the drug frequently fail to correlate with the degree of nephrotoxicity in individual patients. Third, early signs of renal injury can be subtle (e.g., minor changes in electrolyte excretion) or dramatic (e.g., acute renal failure). The subtle changes are particularly important, since they can be useful predictors of serious nephrotoxicity.