A total of 319 clinical isolates known to be resistant to one or more aminoglycoside antibiotics were tested for their susceptibility to 10 aminoglycosides. The percentages of isolates found by an agar dilution method to be susceptible were: amikacin, 83.7%; tobramycin, 41.4%; butirosin A, 33.2%; dideoxykanamycin B, 32.6%; gentamicin C, 27.3%; lividomycin A, 17.6%; neomycin B, 10.7%; paromomycin, 10.3%; kanamycin A, 10.0%; and ribostamycin, 7.2%. The effectiveness of the antibiotics was related to their degree of resistance to bacterial enzymes; e.g., of the nine enzymes known to inactivate antibiotics containing 2-deoxystreptamine, amikacin was affected by one enzyme, tobramycin by five, and gentamicin and kanamycin by six. Examination of cell-free extracts from the 52 strains resistant to amikacin revealed that only four contained the amikacin-inactivating enzyme aminoglycoside-6'-acetyltransferase, a finding indicating that this mechanism of resistance is rare. Other experiments suggest that most amikacin-resistant strains, which are almost invariably resistant to all aminoglycosides, lack the ability to accumulate effectively either amikacin or presumably the other antibiotics intracellularly.

One hundred fifty-two bacterial strains that possess resistance to kanamycin A, gentamicin, or tobramycin, or to more than one of these antibiotics, were collected from various sources in Canada, Europe, Japan, and the United States. This collection was composed of Staphylococcus aureus and Pseudomonas aeruginosa and members of the Enterobacteriaceae family. Their susceptibility to BB-K8 (amikacin), a new broad-spectrum semisynthetic derivative of kanamycin A, and to the other agents, was determined on Mueller-Hinton Medium by the twofold agar dilution method. Test results revealed that 60.5% of the isolates were resistant to 8 gg of tobramycin per ml, 67.1% to 8 ,g of gentamicin per ml, 86.2% to 20 ,g of kanamycin A per ml, and only 8.6% to 20 ig of amikacin per ml. Of interest is the fact that the amikacin-resistant strains were generally resistant to all of the other aminoglycosides. The broad spectrum of amikacin was not totally unexpected, because the compound has been shown to be a poor substrate for most enzymes that inactivate other aminoglycosides through O-phosphorylation, O-adenylylation, or N-acetylation. A number of susceptibility profiles were obtained when the organisms were tested against a series of nine aminoglycosides. The majority of these profiles resembled those found for organisms that possess known mechanisms of enzymatic inactivation.

A course of intravesical mitomycin C, consisting of 8 weekly doses of 30 or 40 mg., was evaluated in 16 patients with superficial bladder cancer (stages O and A). Cystoscopically documented tumor was destroyed completely in 11 patients (69 per cent), while 3 patients exhibited partial tumor regression. Two patients had only multifocal, grade 3 carcinoma in situ and both had a complete response with negative biopsies and cytology at the 12-week evaluation. Toxicity was minimal. Further data, including longer followup, are needed to define the potentially promising role of this agent in the over-all management of superficial bladder cancer.

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