Butirosin Compared with Gentamicin In Vitro and In Vivo

Butirosin (BTN) (P. W. K. Woo, G. L. Coffey, H. W. Dion, S. A. Fusari, and G. D. Senos, U. S. Patent 3,541,078, 1970) is a new aminoglycoside antibiotic notably active against opportunist bacterial species within Pseudomonas, Klebsiella, Enterobacter, Serratia, and Proteus. Numerous comparative tests were carried out with BTN and gentamicin (GTM) in vitro and in experimental infections in mice. BTN was more active in Mueller-Hinton broth than in agar, but its activity was lessened at acid pH or under anaerobiosis, as has been observed with other aminoglycosides. In standard agar diffusion tests, inhibition zones greater than 12 mm around 30-mug BTN disks generally denoted susceptibility, equivalent to minimal inhibitory concentrations [Formula: see text] 25 mug/ml. Cross-resistance between BTN and GTM occurred in a variable manner, with a number of bacterial strains strongly resistant to GTM being moderately susceptible to BTN. In mice, after a single subcutaneous injection, absorption of both antibiotics was rapid, with peak serum levels occurring in 15 min; this was followed by rapid elimination with estimated serum half-lives of about 20 min for each. After peroral administration of high doses in mice, there was no appreciable absorption of BTN. Several tests were carried out to compare BTN and GTM with respect to minimal inhibitory concentrations in vitro, acute subcutaneous median mouse protective doses, peak serum levels at such doses, and the therapeutic ratios derived from acute median protective and lethal doses. Although GTM usually proved to be more potent antibacterially on a weight basis, observations on BTN indicated a superior effectiveness in terms of therapeutic ratios.