[Experimental study in rats on the renal compatibility of cephalothin and cephalothin-aminoglycoside combinations (author's transl)]

Impaired Renal Function Secondary to Gentamicin — Identifying the Special Risk Patient

Although gentamicin has been commercially available since 1969, reports concerning the incidence of nephrotoxicity from this drug and variables relating to this toxicity are still unclear and conflicting. In view of this, a prospective study of patients receiving gentamicin over a two month period was undertaken to determine the incidence of nephrotoxicity and to study the influence of several variables on the potential for developing gentamicin associated nephrotoxicity. The variables studied were patient's age; the total grams of gentamicin received; the total number of days the patient received gentamicin with a hemoglobin of less than 12 g%; sex; total days duration of therapy; hemoglobin prior to therapy; hematocrit prior to therapy; red blood cell count prior to therapy; albumin level prior to therapy; and if the patient received another potentially nephrotoxic drug concomitantly with gentamicin. Sixty patients in total were studied. However, in the “toxic” and “nontoxic” grouping process, seventeen patients were excluded from the study due to missing variables. Of the remaining sample, ten patients were classified as “toxic” and thirty-three were classified as “nontoxic.” Thus the incidence of nephrotoxicity was at least 10/60 or 16.7 percent. The data relating to the variables identified were analysed utilizing Chi-square, t-test, and multiple regression analyses. Two variables were found to be highly significant in relationship to the development of nephrotoxicity while receiving gentamicin therapy. These were (1) the albumin level prior to therapy (lower albumin level in the “toxic” group) and (2) the concomitant use of another potentially nephrotoxic drug. The mechanism behind the influence of albumin on gentamicin toxicity is unclear, but may be related to protein binding. The basis for nephrotoxicity relating to combined use of nephrotoxic drugs is probably additive or synergistic toxicity but this is also unclear.

Until larger prospective studies concerning gentamicin associated nephrotoxicity provide more meaningful information concerning the significance of the variables involved in this adverse reaction, caution is recommended when using this drug in the albumin deficient patient or in combination with nephrotoxic drugs. In addition, it is further recommended that in patients receiving gentamicin, renal function should be closely monitored and the dosage regimen determined accordingly.

Tobramycin nephrotoxicity: failure of cefotaxime to potentiate renal toxicity

The aim of our prospective clinical study was to determine whether the combination of tobramycin plus cefotaxime is more nephrotoxic than tobramycin alone. The studies were carried out in 30 patients with serious infections and normal renal function. Groups of ten patients each received either 2 g cefotaxime or 1 mg/kg body weight tobramycin or cefotaxime and tobramycin in the same dosage every eight hours intravenously for at least seven days. Serum creatinine, creatinine clearance and alanine aminopeptidase (AAP) excretion in 24-hour urine were determined before, during and five days after the antibiotics had been discontinued. These were used as parameters for glomerulotubular injury. The plasma levels of tobramycin and cefotaxime (assayed by agar diffusion) did not differ when the drugs were given alone or in combination. None of the patients treated with cefotaxime alone showed any signs of renal damage. In contrast, tobramycin alone or in combination with cefotaxime caused an increase in urinary enzymes in all patients. This activity was a mean five to six times greater than the initial values prior to antibiotic therapy. There were no significant differences between the AAP increase during treatment with tobramycin and tobramycin plus cefotaxime. Four to five days after discontinuing antibiotic therapy, AAP activity decreased to values similar to those measured prior to therapy. In some of the patients receiving tobramycin alone or in combination with cefotaxime, increased creatinine levels, a reduction in creatinine clearance to 60 ml/min and an increase in renal enzyme excretion could be observed. Thus, treatment with high doses of cefotaxime does not seem to increase tobramycin nephrotoxicity in patients with normal renal function. The nephrotoxicity of this drug combination is obviously due to the aminoglycoside.

[Nephrotoxicity of cefsulodin: experimental studies in animals (author's transl)]

Experimental investigations in wistar rats indicate that cefsulodin, a new cephalosporin antibiotic with high activity against Pseudomonas aeruginosa, is more nephrotoxic than cephaloridine, the cephalosporin with the lowest renal tolerance up until new. Therefore, when cefsulodin is used clinically, renal function should be carefully controlled.

Effect of cefamandole nafate on the toxicity of tobramycin

Because of the potential for an interaction between cephalosporins and aminoglycosides leading to renal injury, an evaluation of the effect of a new cephalosporin, cefamandole nafate, on the toxicity of the aminoglycoside tobramycin was performed in laboratory animals. High doses of cefamandole nafate did not increase the acute toxicity (lethality) of tobramycin in rats or mice. In a subacute experiment in rats, dose-related tobramycin nephrotoxicity, as evidenced by blood urea nitrogen changes, increased kidney weights, and histologically determined tubular nephrosis and necrosis, was observed. Concomitant treatment with cefamandole nafate, 500 mg/kg, did not increase tobramycin nephrotoxicity, but protected against the aminoglycoside-induced renal injury. Determination of tissue radioactivity after administration of [(14)C]tobramycin indicated that cefamandole nafate treatment resulted in uniformly lower tobramycin tissue concentrations compared with the control, suggesting that the protective effect was produced by enhanced excretion of tobramycin after cefamandole nafate treatment.

[Experimental studies on the renal tolerance of cefuroxime (author's transl)]

The potential renal tolerance of cefuroxime was investigated in 80 female albino Wistar rats and compared with that of cephacetrile. The drugs were administered i.m. in different dosages (1000, 2000, 3000 and 5000 mg/kg/day; dosage interval: 12 h) over a period of five days. The excretion of tubular cells and urinary malic dehydrogenase was assessed before, during and after administration of the antibiotics. In addition, the concentration of serum urea was analysed and the renal histology was examined. The following toxic threshold doses were estimated: cefuroxime 5000 mg/kg/day, cephacetrile 3000 mg/kg/day. In comparison with other cephalosporines cefuroxime belongs to those antibiotics with which a high degree of renal tolerance is demonstrated.