tetracycline and dirithromycin

A national study was conducted to determine the in vitro activity of 2 newer macrolides, dirithromycin and erythromycylamine compared with that of erythromycin, tetracycline and penicillin. Nineteen major teaching hospitals participated in the study. Minimal Inhibitory Concentrations (MICs) were determined by agar dilution, mostly using Iso-Sensitest Agar and an inoculum of 10(4) cells per spot. 2284 clinically significant strains were isolated in late 1991 and early 1992, comprising 1736 Gram-positive cocci, 355 Haemophilus influenzae, 97 Moraxella catarrhalis, 32 Listeria monocytogenes, 25 Neisseria meningitidis and 39 Neisseria gonorrhoeae were tested. The study indicates that dirithromycin and erythromycylamine possess antibacterial activity equivalent to that of erythromycin against most Gram-positive cocci and M. catarrhalis. Strains resistant to erythromycin were also resistant to dirithromycin and to erythromycylamine. Tetracycline was as active as the macrolides against both penicillin-resistant and penicillin-susceptible strains of Staphylococcus aureus. Coagulase-negative penicillin-resistant staphylococci, compared with tetracycline, were relatively resistant to the macrolides. H. influenzae was less susceptible than the Gram-positive cocci.

Topics: Anti-Bacterial Agents; Australia; Drug Resistance, Microbial; Erythromycin; Gram-Negative Bacteria; Gram-Positive Bacteria; Hospitals, Teaching; Humans; Macrolides; Microbial Sensitivity Tests; Moraxella catarrhalis; Penicillins; Respiratory Tract Infections; Tetracycline

Dirithromycin is a new macrolide antibiotic that achieves high tissue concentration. We compared its in vitro activity against Mycoplasma species with that of erythromycin and tetracycline. Clinical isolates of M. pneumoniae (40), M. hominis (40), and Ureaplasma urealyticum (40) were tested against serial dilutions of three antibiotics using a microtiter plate method. Minimum inhibitory concentrations (MIC) were read as the lowest concentration of antibiotic yielding no color change in the broth. Neither macrolide antibiotic exhibited antimicrobial activity against M. hominis; MIC50 and MIC90 for tetracycline were 0.6 and 32 micrograms/ml, respectively. MIC50 for U. urealyticum was 4.0 micrograms/ml for dirithromycin, 2.0 micrograms/ml for erythromycin, and 1.0 micrograms/ml for tetracycline. MIC90 for U. urealyticum was > 128 micrograms/ml for all three agents. Against M. pneumoniae dirithromycin exhibited MIC50 of 0.1 micrograms/ml and MIC90 of 0.1 micrograms/ml. Both values for erythromycin were 0.2 micrograms/ml; for tetracycline they were 0.1 and 1.0 micrograms/ml, respectively. These results demonstrate the high in vitro activity of dirithromycin against M. pneumoniae and suggest that this agent may have a role in the treatment of respiratory Mycoplasma infections.

Topics: Anti-Bacterial Agents; Erythromycin; Macrolides; Microbial Sensitivity Tests; Mycoplasma; Tetracycline