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• We reviewed the charts of 163 patients with 183 episodes of Gram-negative bacillary bacteremia to determine a clinical profile that would select patients at high risk for experiencing gentamicin-sulfate-resistant Gram-negative bacillary bacteremia at our hospital. Gentamicin-resistant Gram-negative bacilli were only associated with institution-acquired bacteremia. Among institution-acquired episodes, urinary tract infection, diagnostic or therapeutic procedures of the lower respiratory tract or urinary tract, presence of pneumonic infiltrate on chest roentgenogram, prior therapy with gentamicin, and prior therapy with other antibiotics were significant risk factors. Because only two of the 29 gentamicin-resistant bacteria that were tested against amikacin base were resistant to amikacin, we advocate initial treatment with amikacin for patients with evidence of an institution-acquired Gram-negative bacteremic episode. Gentamicin is still our initial choice for a community-acquired episode.(Arch Intern Med 1981;141:582-586)

A number of new β-lactam antibiotics have been developed to overcome bacterial resistance to older agents. Such resistance usually is caused by plasmid-mediated, constituently produced β-lactamases. Second- and third-generation cephalosporins, ureidopenicillins, acylamino penicillins, and monobactams generally are resistant to hydrolysis by these enzymes. However, inducible β-lactamases may confer resistance to these antibiotics. This induction may occur spontaneously or in response to cefoxitin or other β-lactam agents. The mechanisms by which inducible enzymes produce this resistance are reviewed and implications for the prophylactic and therapeutic use of newer β-lactams are considered.