Zithromax - Clinical Pharmacology

(Page 4)

There are no pharmacokinetic data available from studies in hepatically-or renally-impaired individuals. The effect of azithromycin on the plasma levels or pharmacokinetics of theophylline administered in multiple doses adequate to reach therapeutic steady-state plasma levels is not known. (See PRECAUTIONS.) Mechanism of Action: 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.

Microbiology

Azithromycin has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section. Aerobic Gram-Positive Microorganisms Staphylococcus aureus Streptococcus agalactiae Streptococcus pneumoniae Streptococcus pyogenes NOTE: Azithromycin demonstrates cross-resistance with erythromycin-resistant gram-positive strains. Most strains of Enterococcus faecalis and methicillin-resistant staphylococci are resistant to azithromycin.

Aerobic Gram-Negative Microorganisms Haemophilus influenzae

Moraxella catarrhalis "Other" Microorganisms Chlamydia trachomatis

Beta-lactamase production should have no effect on azithromycin activity.

Azithromycin has been shown to be active in vitro and in the prevention and treatment of disease caused by the following microorganisms:

Mycobacteria Mycobacterium avium complex (MAC) consisting of:

Mycobacterium avium Mycobacterium intracellulare.

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.