Mechanism of Action: Azithromycin

Azithromycin acts by binding to the 50S ribosomal subunit of susceptible microorganisms and thus, interfering with microbial protein synthesis. Nucleic acid synthesis is not affected.

Azithromycin concentrates in phagocytes and fibroblasts as demonstrated by in vitro incubation techniques. Using such methodology, the ratio of intracellular to extracellular concentration was >30 after one hour incubation. In vivo studies suggest that concentration in phagocytes may contribute to drug distribution to inflamed tissues.

Trovafloxacin and azithromycin have both been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections (see INDICATIONS).

Aerobic gram negative microorganisms

Neisseria gonorrhoeae

"Other" Microorganisms

Chlamydia trachomatis

Information on the in vitro activity of either trovafloxacin or azithromycin may be found in the respective prescribing information of these products.

Susceptibility Tests:

Trovafloxacin

Dilution Techniques: Quantitative methods are used to determine antimicrobial minimum inhibitory concentrations MICs. These MICs provide estimates of the susceptibility of bacteria to antimicrobial compounds. The M.C. should be determined using a standardized procedure. Standardized procedures are based on dilution methods¹ (broth or agar) or equivalent with standardized inoculum concentrations and standardized concentrations of trovafloxacin mesylate powder. The MIC values should be interpreted according to the following criteria: For testing Neisseria gonorrhoeae ^a:

A report of "Susceptible" indicates that the pathogen is likely to be inhibited if the antimicrobial compound in the blood reaches the concentration usually achievable. A report of "Intermediate" indicates that the result should be considered equivocal, and if the microorganism is not fully susceptible to alternative, clinically feasible drugs, the test should be repeated. This category implies possible clinical applicability in body sites where the drug is physiologically concentrated or in situations where high dosage of drug can be used. This category also provides a buffer zone which prevents small uncontrolled technical factors from causing major discrepancies in interpretation. A report of "Resistant" indicates that the pathogen is not likely to be inhibited if the antimicrobial compound in the blood reaches the concentration usually achievable; other therapy should be selected.

Standardized susceptibility test procedures require the use of laboratory control microorganisms to control the technical aspects of the laboratory procedures. Standard trovafloxacin mesylate powder should provide the following MIC values:

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