MACROLIDES Erythromycin Clarithromycin Azithromycin Mechanism of action Inhibit protein synthesis by binding to the 50 s subunit Antibacterial activity Bactericidal or bacteriostatic, depending on the concentration and type of bacteria

Macrolides ( cont. ) Pharmacokinetics Erythromycin base Absorption incomplete but adequate from intestine Inactivated by gastric HCL, hence given as : Enteric coated tablets or ester (stearate, ethyl succinate ) Food delays absorption Not metabolized and actively secreted in bile ( major route of excretion ) Only 2-5 % is excreted in active form in urine Widely distributed into most tissues, except the brain and CSF Cross the placental barrier Protein binding – % Half – life approx. 1.6 hr

Clarithromycin Pharmacokinetics Acid stable Food delays absorption but does’nt alter its extent Metabolized by the liver to 14- hydroxy clarithro. ( active ) Widely distributed, except brain and CSF Protein binding 40 – 70 % Excreted in Urine – unchanged 20 – 40 % 14- H. clarithromycin 10 – 15 % Biliary Half- life clarithromycin 3 – 7 hr 14 – H. clarithromycin 5- 9 hr Advantage over erythromycin Lower frequency of GI intolerance Less frequent dosing ( twice daily )

MACROLIDES ( cont. ) Azithromycin Pharmacokinetics Rapidly absorbed from GIT Food delays absorption Widely distributed ( extensive tissue distribution ), except CSF Protein binding 51% Undergo some hepatic metabolism ( inactive ) Biliary route is the major route of elimination Only 6% is excreted unchanged in the urine Half- life approx. 3 days Advantage over erythromycin & clarithromycin Once daily dosing No inhibition of cytochrome P- 450

Macrolides ( cont. ) Antibacterial spectrum Erythromycin – Mainly effective on G+ bacteria A. Gram- positive bacteria Staph. Aureus S. pneumoniae URTIs ( eg. Otitis media, pharyngitis ) LRTIs ( eg. Pneumoniae ) S. pyogens C. diphtheria B. Gram- negative bacteria T. pallidum C. Intracellular organisms L. pneumophila M. pneumoniae C. trachomatis

Indications for erythromycin 1. Alternative to penicillin in allergic pts ( Staph.Aureus, S. pyogens, S.pneumoniae or T.pallidum ) 2. Diphtheria & whooping cough – drug of choice 3. Legionnaires disease- drug of choice 4. Pneumoniae ( M. pneumoniae ) – children 5. Chlamydia trachomatis

Clarithromycin Antibacterial spectrum A. Gram- positive bacteria Staph. Aureus S. Pneumoniae S. Pyogens B. Gram- negative bacteria H. influenzae H. Pylori M. catarrhalis C. Intracellular organisms M. pneumoniae L. Pneumophila Indications Pharyngitis / tonsilitis Otitis, sinusitis Adjunct in treatment of duodenal ulcer ( H. pylori )

Azithromycin Mainly effective on G- bacteria but less active against G+(s.pneumoniae & s.pyogenes) than erythromycin Antibacterial spectrum A. Gram- positive bacteria Staph. Aureus S. Pneumoniae S. Pyogens B. Gram- negative bacteria (> erythromycin) M. catarrhalis H. influenzae C. Intracellular organisms (> erythromycin) L. Pneumophila M. pneumoniae Chlamydia species Indications Pharyngitis/ tonsilitis ( s. pyogens ), otitis, sinusitis ( Staph. Aureus & H. influenzae ) Uncomplicated genital chlamydial infections

Side effects of macrolides Nausea, vomiting, abdominal pain & diarrhea( AAC) Allergic reactions- urticaria, mild skin rashes Sore mouth