In children, steroid-resistant nephrotic syndrome due to focal segmental glomerulosclerosis (FSGS) is frequently a progressive condition resulting in end-stage renal disease. There have been no reports of effective treatment for this condition. For the past several years, the Pediatric Nephrology services at the University of California, San Diego and Stanford University Schools of Medicine have treated these patients with a protocol involving infusions of high doses of methylprednisolone, often in combination with oral alkylating agents. Twenty-three children have been treated in this manner with a follow-up of 46 +/- 5 months. Twelve of these children are in complete remission. Six have minimal to moderate proteinuria. Four children remain nephrotic. Each of these children has a normal glomerular filtration rate. One child developed chronic renal failure and subsequently died while on dialysis. These results appear significantly better than previous series of children with FSGS. A controlled, multi-center trial of this protocol has been proposed.

The nephrotoxic beta-lactam antibiotics cause acute proximal tubular necrosis. Significant renal toxicity, which has been rare with the penicillins and uncommon with the cephalosporins, is a greater risk with the penems. Mechanisms of injury include: (1) transport into the tubular cell, mainly through the antiluminal organic anion secretory carrier; (2) acylation of target proteins, causing respiratory toxicity by inactivation of mitochondrial anionic substrate carriers; and (3) lipid peroxidation. The most nephrotoxic beta-lactams available for study are cephaloridine, cephaloglycin, and imipenem; panipenem, which is comparably nephrotoxic, is currently available only in Japan. Cephaloridine has several unique properties, probably all caused by its pyridinium side-group: (1) its secretory transport into the tubular cell is followed by minimal cell to luminal fluid movement, resulting in extreme intracellular sequestration; (2) it is the only beta-lactam shown to cause significant oxidative injury; (3) it has a limited ability to attack the mitochondrial carriers for pyruvate and the short-chain fatty anions. Cephaloglycin and imipenem undergo less intracellular trapping than cephaloridine, but have sufficient tubular cell uptake, reactivity, and generalized toxicity to mitochondrial substrate carriers to be severely nephrotoxic. Cephaloridine and cephaloglycin are no longer used clinically. Imipenem and panipenem are marketed in combination with nephroprotective renal transport inhibitors. Strategies for avoiding renal toxicity with new cephalosporins and penems are discussed.

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Large doses of cephaloridine cause acute necrosis of the proximal renal tubule that can be prevented by probenecid and other organic anions. Although there is little or no net secretion of cephaloridine by the mammalian kidney, the degree of cephaloridine uptake by the cortex of the rabbit kidney is substantial; this uptake is also prevented by probenecid and other organic anions. Cortical concentrations of cephaloridine were measured in control and probenecid-treated animals of different mammalian species. Evidence of cephaloridine trnsport was found in the guinea pig and the rat as well as in the rabbit. The degree of reduction of cortex-to-serum ratios by probenecid (control cortex-to-serum minus probenecid-treated cortex-to-serum ratios) correlated with the sensitivity to the nephrotoxicity of the drug. This degree or reduction was greatest in the rabbit, intermediate in the guinea pig, and least in the rat. In addition, the newborn rabbit, which is more resistant to the toxicity of cephaloridine than the adult, also had significantly lower cortical concentrations of cephaloridine. Finally, the acute tubular necrosis produced by extremely large doses of cefazolin in the adult rabbit was prevented by probenecid. It was concluded (1) that the nephrotoxicity of cephaloridine is related to its renal cortical transport with high intracellular concentrations of drug; and (2) that this relationship between transport and toxicity exists for cefazolin as well, although the toxicity is of a different order of magnitude. The unusual mechanism of cephaloridine transport in the proximal tubule was contrasted with that of the other cephalosporins in an attempt to explain its greater degree of nephrotoxicity.