The following in vitro data are available, but their clinical significance is unknown. Azithromycin exhibits in vitro minimal inhibitory concentrations (MICs) of 2.0 µ g/ mL or less against most ( 90%) strains of the following microorganisms; however, the safety and effectiveness of azithromycin in treating clinical infections due to these microorganisms have not been established in adequate and well-controlled trials. Aerobic Gram-Positive Microorganisms Streptococci (Groups C, F, G) Viridans group streptococci Aerobic Gram-Negative Microorganisms Bordetella pertussis Campylobacter jejuni Haemophilus ducreyi Legionella pneumophila Anaerobic Microorganisms Bacteroides bivius Clostridium perfringens Peptostreptococcus species "Other" Microorganisms Borrelia burgdorferi Mycoplasma pneumoniae Treponema pallidum Ureaplasma urealyticum Susceptibility Testing of Bacteria Excluding Mycobacteria The in vitro potency of azithromycin is markedly affected by the pH of the microbiological growth medium during incubation. Incubation in a 10% CO2 atmosphere will result in lowering of media pH (7.2 to 6.6) within 18 hours and in an apparent reduction of the in vitro potency of azithromycin. Thus, the initial pH of the growth medium should be 7.2-7.4, and the CO2 content of the incubation atmosphere should be as low as practical. Azithromycin can be solubilized for in vitro susceptibility testing by dissolving in a minimum amount of 95% ethanol and diluting to working concentration with water. Dilution Techniques: Quantitative methods are used to determine minimal inhibitory concentrations that provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. One such standardized procedure uses a standardized dilution method 1 (broth, agar or microdilution) or equivalent with azithromycin powder. The MIC values should be interpreted according to the following criteria: | ||||
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