Tuesday, September 20, 2011

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Azithromycin - macrolide


Antimicrobial activity:
Good against Gram positive and Gram negative organisms. Slightly less active than erythromycin against staphylococci and streptococci but more active against H.influenzae. It is also highly active against chlamydia, Mycobacterium avium complex and Toxoplasma gondii.

Mechanism of action:
It binds to the 50s ribosome subunit and hinders the translocation of the elongated peptide chain from the acceptor site to the peptidyl site. Thus the ribosome does not move along the mRNA to expose the next codon and peptide synthesis is prematurely terminated.

Pharmacokinetic properties:
Acid stability and more active in alkaline medium,
rapid oral absorption but better given 1 hour before meals or 2 hours after meals,
marked tissue distribution especially intracellular penetration (macrophages and fibroblasts),
Half life : 2-4 days, therefore can be given as once a day dosing

Clinical uses:
1) Legionnaire's pneumonia - 500 mg O.D for 2 weeks (drug of choice)
2) Chlamydia trachomatis - 1 g single dose (drug of choice)
3) pharyngitis, tonsillitis, sinusitis, otitis media, pneumonias, gonorrhea, acute exacerbation of chronic bronchitis - 500 mg O.D for 3 days for uncomplicated cases.


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