April 18, 2022

AZITHROMYCIN

 

Introduction: Azithromycin, a 15-atom lactone macrolide ring compound, is derived from erythromycin by addition of a methylated nitrogen into the lactone ring. Its spectrum of activity, mechanism of action, and clinical uses are similar to those of clarithromycin. Azithromycin is active against M. avium complex and T. gondii. Mycobacteria:  Azithromycin is slightly less active than erythromycin and clarithromycin against staphylococci and streptococci and slightly more active against H. influenzae. Azithromycin is highly active against Chlamydia sp. H.influenzae

Pharmacokinetic aspects of the drug: Azithromycin differs from erythromycin and clarithromycin mainly in pharmacokinetic properties. A 500-mg dose of azithromycin produces relatively low serum concentrations of approximately 0.4 mcg/mL. However, azithromycin penetrates into most tissues (except cerebrospinal fluid) and phagocytic cells extremely well, with tissue concentrations exceeding serum concentrations by 10- to 100-fold. The drug is slowly released from tissues (tissue half-life of 2–4 days) to produce an elimination half-life approaching 3 days. These unique properties permit once-daily dosing and shortening of the duration of treatment in many cases. For example, a single 1-g dose of azithromycin is as effective as a 7-day course of doxycycline for chlamydial cervicitis and urethritis.

Pharmacological Applications: Community-acquired pneumonia can be treated with azithromycin given as a 500-mg loading dose, followed by a 250-mg single daily dose for the next 4 days. A zithromycin is rapidly absorbed and well tolerated orally. It should be administered 1 hour before or 2 hours after meals. Aluminum and magnesium antacids do not alter bioavailability but delay absorption and reduce peak serum concentrations. Azithromycin does not inactivate cytochrome P450 enzymes and, therefore, is free of the drug interactions that occur with erythromycin and clarithromycin.  

RELATED;

1.  The cytochrome P450 enzyme system

2.  Pharmacology test questions

3.  Pharmacology and therapeutics

[REFERENCE]

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