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Healthcare Communications

Azithromycin

 

 

Azithromycin


- Macrolide antimicrobial
- Differs from erythromycin in having amino substituted expanded macrolide nucleus
- Structural differences provide better pharmacokinetics

 

 

Mechanism of Action

- Inhibits protein synthesis by binding to
50S ribosomal subunit of bacteria
- Better gram negative coverage than erythromycin

 

Antimicrobial activity

- Staphylococcus aureus & Staph.epidermidis
- Streptococcus pyogenes, S.agalactiae, S.viridans, S.pneumoniae
- Bordetella pertussis, B.parapertussis
- Campylobacter jejuni
- Helicobacter pylori
- Haemophilus influenzae, H.parainfluenzae
- Moraxella catarrhalis
- Neisseria gonorrhoeae, N.meningitidis
- Gardnerella vaginalis
- Bacteroides melaninogenicus
- Clostridium perfringens
- Propionibacterium acnes
- Chlamydia trachomatis, C. pneumoniae
- Mycoplasma pneumoniae
- Ureaplasma urealyticum

 

 

Pharmacokinetics

- More stable than erythromycin in gastric acid
- Pharmacokinetics characterised by rapid passage from circulation into intracellular compartment, followed by slow release
- Concentration in tissues, organs, tissue fluids and cells is more than in blood
- High intracellular penetration tackles difficult
-to-reach organisms proliferating intracellularly e.g., Chlamydia, Mycobacterium, Legionella
- Metabolised in liver; unchanged drug excreted in urine and faeces
- Pharmacokinetics nor significantly altered in elderly or in patients with mild renal or hepatic impairment

 

Indications

- Urogenital infections & STD : Single dose covers C.trachomatis, N.gonorrhoeae, U.urealyticum & H.ducreyi
- LRTI : Acute exacerbations of chronic bronchitis, pneumonia, other RTI
- URTI & ENT Infections: pharyngitis, otitis media, sinusitis
- Skin & Soft Tissue Infections : dermatological infections & surgical wound infection
- AIDS patients with M.avium infection 500 mg administered over 10-30 days reduces mycobacteraemia and clinical symptoms

 

Dosage

Usual dose for otitis media, RTI and skin infections :
500 mg single dose daily for 3 days or 500 mg initially and 250 mg daily for further 4 days

Chlamydia trachomatis infection:
1 gm as a single dose

Gonorrhoea:
1 gm as a single dose

Children 10 mg/kg on first day;
5 mg/kg for next 2-5 days

 

Tolerability

- Well tolerated; better tolerated than erythromycin
- Usual adverse effects are gastrointestinal (nausea, diarrhoea, abdominal pain)
- No important drug interactions; though heavy meal may interfere with absorption

 

 

Advantages over Erythromycin

- Better stability in gastric acid
- 37% bioavailability vs. 25% with erythromycin
- Higher and more sustained tissue/intracellular concentrations
- Once daily x 3 days dosing vs. q.i.d. x 5-10 days dosing with erythromycin
- Greater coverage of gram negative bacteria

 

 

Advantages over Clarithromycin

- Greater coverage of gram negative bacteria
- Once daily x 3 days dosing vs. b.i.d. x 10 days dosing with clarithromycin
- More economical than clarithromycin