Azithromycin is a macrolide antibacterial with a broad and essentially bacteriostatic action against many Gram-positive and to a lesser extent some Gram-negative bacteria, as well as other organisms including Mycoplasmas spp., Chlamydiaceae, Rickettsia spp.,and spirochaetes. Azithromycin and other macrolides bind reversibly to the 50S subunit of the ribosome, resulting in blockage of the transpeptidation or translocation reactions, inhibition of protein synthesis, and hence inhibition of cell growth. Its action is predominantly bacteriostatic but high concentrations are slowly bactericidal against the more sensitive strains. Because macrolides penetrate readily into white blood cells and macrophages there has been some interest in their potential synergy with host defence mechanisms in vivo. It is active in vitro against some Gram-negative pathogens such as Haemophilus influenzae and Moraxella catarrhalis (Branhamella catarrhalis), as well as having activity against some of the Enterobacteriaceae such as Escherichia coli, Salmonella and Shigella spp. Azithromycin is also active against Chlamydia trachomatis and some opportunistic mycobacteria, including Mycobacterium avium complex. It has activity against the protozoa Toxoplasma gondii and Plasmodium falciparum.
Following oral administration about 40% of a dose of Azithromycin is bioavailable. Peak plasma concentrations are achieved 2 to 3 hours after a dose, but Azithromycin is extensively distributed to the tissues, and tissue concentrations subsequently remain much higher than those in the blood. High concentrations are taken up into white blood cells. There is little diffusion into the CSF when the meninges are not inflamed. Small amounts of Azithromycin are demethylated in the liver, and it is excreted in bile as unchanged drug and metabolites. About 6% of an oral dose is excreted in the urine. The terminal elimination half-life is about 68 hours.
Azithromycin (zithrox) has a wide spectrum of activity and may be used to treat a wide range of infections caused by the following susceptible organisms
(a) Gram positive: Streptococcus pneumoniae, Str. pyogenes, Staphylococcus aureus, Baccillus anthracis, Corynebacterium diptheriae and Clostridium spp.
(b) Gram negative: Neisseria menengitidis, N. gonorrhoeae, Moraxella catarrhalis, Bordetella spp, Listeria monocytogenes, Brucella spp, Haemophilus ducreyi, H. influenzae, Helicobacter pylori and Campylobacter jejuni.
(c) Others sensitive: Actinomyces spp, Chlamydia, rickettsias, Treponema pallidum, some mycoplasmas and mycobacteria.
Azithromycin may also be used as a component of regimens in the prophylaxis and treatment of opportunistic infections like Mycobacterium avium complex (MAC) and may be used for prophylaxis