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Pharmacology: Pharmacodynamics and Pharmacokinetics: Like other macrolides, azithromycin inhibits RNA-dependent protein synthesis by binding to the 50S ribosomal sub unit of the 70S ribosome of susceptible bacteria. The site of action appears to be the same as that of the macrolides, clindamycin, lincomycin, and chloramphenicol. Azithromycin is less active than erythromycin against streptococci and staphylococci, but has greater activity in vitro against some Gram-negative organisms such as Haemaphilus influenzae and Moraxella catarrhalis (Branhamella catarrhalis), as well as having activity against same of the Enterabacteriaceae such as Escherichia coli, Salmonella and Shigella spp. Azithromycin is also more active than erythromycin against Chlamydia trachomatis and Ureaplasma urealyticum and same opportunistic mycobacteria including Mycobacterium avium complex. Azithromycin is active against the protozoa Taxoplasma gondii and Plasmodium falciparum.
Azithramycin is rapidly absorbed after oral intake and achieves peak plasma concentration in about 2-3 hours. Azithromycin is extensive distributed into the tissues and there is little diffusion into the CSF when the meninges are not inflamed. Excretion is main in bile as an unchanged drug it has terminal elimination half-life of about 68 hours.
