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Three combinations of antibiotics (cephalothin-tobramycin, cephalothinticarcillin, and ticarcillin-tobramycin) were administered empirically to 186 patients with cancer who were suspected of having a life-threatening infection. In approximately one-half of these patients, gram-negative infection was documented bacteriologically and consisted of septicemia in 50% of these patients. The three antimicrobial regimens were similarly effective and resulted in a favorable clinical response in approximately 55% of the patients. The administration of the cephalothin-tobramycin combination was associated with a significantly higher frequency of nephrotoxicity than that of the other two regimens.In patients with cancer, especially when neutropenia is present, gram-negative bacterial infections are a major cause of death (1,8). Under these clinical circumstances, various antimicrobial regimens have been recommended; among them are the combinations of carbenicillin with gentamicin (15), carbenicillin with cephalothin (12), cephalothin with gentamicin (7), and multiple drug regimens including car-benicillin, cephalothin, and gentamicin (9) or carbenicillin, cephalothin, gentamicin, methicillin, and clindamycin (17).In the present study we have compared the combination of ticarcillin with cephalothin (Tic-Cef) to that of ticarcillin with tobramycin (Tic-Tob) and of cephalothin with tobramycin (Cef-Tob). Ticarcillin Therapy with Tic-Cef, Tic-Tob, or Cef-Tob was chosen at random using a table of randomized numbers. Therapy was started without waiting for the isolation and identification of the offending microorganisms. Ticarcillin (10 g) and cephalothin (3 g) were given intravenously, three times daily, over a period of 20 min, each drug being dissolved in 100 ml of 5% dextrose. Tobramycin was given intramuscularly (except in thrombopenic patients) three times daily; the dosage was calculated to represent a total daily dose of approximately 4.5 mg/kg; when given intravenously, tobramycin was dissolved in 100 ml of 5% dextrose and administered over a 20-min period.

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Gentamicin and tobramycin have been compared in vitro and as single-drug therapy in patients with a serious infection caused by gram-negative rods. In vitro, a slight advantage of tobramycin over gentamicin has been found against Pseudomonas aeruginosa. Cross-resistance between gentamicin and tobramycin has been observed for gentamicin-resistant strains of P. aeruginosa and Providence but was not always present. The clinical effectiveness of gentamicin and tobramycin was similar: 14 (45.1%) out of the 31 patients in each series responded favorably. The clinical results were much better in urinary tract infections (66% of favorable responses) than in wound infections, pulmonary infections, septicemia, and meningitis (26% of favorable responses). The frequency of adverse reactions encountered in the present series was similar for both drugs.Tobramycin is a new aminoglycoside antibiotic that has been reported to present an antibacterial activity similar to that of gentamicin against most strains of Enterobacteriacae and Staphylococcus. However, it has been suggested by several in vitro studies that tobramycin might have an anti-Pseudomonas advantage over gentamicin (5,9,12).Only a few clinical investigations using tobramycin have been reported