Letter: Severe renal dysfunction after tobramycin/cephalothin therapy

Tobramycin in ophthalmology

Selman Waksman's laboratory at Rutgers University discovered the first aminoglycoside antibiotic, streptomycin, in 1943. Other aminoglycoside antibiotics, such as gentamicin and tobramycin, soon followed. Tobramycin is compatible with most intravenous fluids and tear substitutes, but it is incompatible with heparin and some beta-lactam antibiotics such as penicillin and cephalosporins. Due to tobramycin's broad spectrum of activity, it has proven useful in controlling both superficial and deep infections of the eye and ocular adnexa (i.e., blepharitis, conjunctivitis, keratitis, and endophthalmitis). However, since tobramycin has been associated with neuromuscular blockade, as well as possessing ototoxic and nephrotoxic effects, care must be taken to minimize toxicity by monitoring patients undergoing systemic tobramycin therapy.

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.

Empiric treatment of fever in acute leukaemia with tobramycin-cephalothin, and the escape clause provision of corticosteroids

29 episodes of suspected septicaemia in patients with acute leukemia were treated empirically with tobramycin 180--240 mg/day intravenously together with cephalothin 12 g/day. Patients without documented infection who did not respond to antibiotics and whose fever developed after a course of cytotoxic drugs, were given the provision of high dose corticosteroid therapy. Infection was documented microbiologically or clinically in 13/29 episodes. Septicaemia was proven in 7, and 6 had pneumonia. Neutropenia was present in 18/29 episodes. A satisfactory response to initial therapy was achieved in 7/13 with documented infection and in 9/16 without proven infection. The overall good response was 55%, 5/7 cases with septicaemia, but only 2/6 with pneumonia responded well. The 2 septicaemia patients who did not respond had Pseudomonas aeruginosa sepsis. In 16 episodes without documented infection 7 did not respond to initial therapy. To 4 of them, who were subject to recent cytotoxic drug administration, high dose corticosteroid therapy was given, and 3 of them responded well. Of the remaining 3 non-responders, one became afebrile after cytostatic and one after prednisolone treatment. Serum assays of tobramycin were done on the 1st and 5th day of therapy and no difference in concentration was observed on these 2 occasions. Five patients developed renal failure, but this was attributed to antibiotic therapy only in 1, who initially had an elevated serum creatinine. It is concluded, that in hospitals where pseudomonas is not a dominating pathogen, tobramycin--cephalothin may be a good combination to start empiric therapy with. In patients without proven infection, who have recently been subjected to cytotoxic therapy, and who do not respond to the initial course of antibiotics, a high dose of corticosteroids may be tried, provided the patient is monitored for the hazard of bacterial infection.

Tobramycin in the treatment of severe and complicated urinary tract infections

Tobramycin is an aminoglycoside aminocyclitol antibiotic with pharmacological similarities to gentamycin. Twenty-one of 30 patients with a severe or complicated Gram-negative urinary tract infection were cured by treatment with a 5-day course of tobramycin. No side effects were noted. This drug should prove beneficial for the treatment of severe Gram-negative sepsis, and promises to be particularly valuable for infections due to Pseudomonas aeruginosa. Dosage schedules for administering tobramycin to patients with renal function impairment are presented, together with some observations on its intravenous injection by bolus. A single dose of tobramycin has proved effective for initiating the antibacterial treatment of patients with acute pyelonephritis. The important concept of the differing concentrations of an antibiotic in the urine from kidneys of unequal function is discussed.