In vitro activities of beta-lactam and aminoglycoside antibiotics. A comparative study of 20 parenterally administered drugs.

In vitro susceptibilities of 552 recent clinical isolates to 20 parenterally administered beta-lactam and aminoglycoside antibiotics were studied. Newer beta-lactam antibiotics had no increased activity over well-known penicillins and cephalosporins against Gram-positive cocci. All showed greater activity, a broadened spectrum, or both against Gram-negative bacilli; azlocillin, mezlocillin, mecillinam, cefamandole, and cefoxitin each had unique advantages. Against Bacteroides fragilis, mezlocillin was more active than available penicillins, and cefoxitin was more active than available cephalosporins, but neither provided any advantages against other anaerobes. All the aminoglycosides studied were inactive against streptococci and anaerobes but had broad spectrums of activity against staphylococci and Enterobacteriaceae. Activity against Pseudomonas aeruginosa was variable. Sisomicin was the most active aminoglycoside against aminoglycoside-susceptible Gram-negative bacilli, but amikacin inhibited the largest percentage (99.2%) of Enterobacteriaceae and P aeruginosa.