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Bacterial Protein Synthesis Inhibitors, 1) Pharmacokinetics 2)…

- - - - Absorption
        
        Erythromycin base is acid labile - use enteric coated tabs / ester forms
        
        Food inhibits absorption of all macrolides - except Clarithromycin
        Distribution
        
        ↑Vd - Erythromycin & Clarithromycin
        
        Azithro & Clarithromycin -concentrated in neutrophils, macrophages & fibroblasts
        Excretion
        
        Metabolized in liver & excreted in bile - except Clarithromycin (Dose must be ↓in renal failure
        as it's excreted in urine)
        
        Erythromycin - QID dosing, Clarithro - BD, Azithro - OD
        
        all are inhibitors of CYP enzymes - except Azithro
    - - Erythromycin, Roxithromycin = Penicillin G - GP cocci & bacilli
        
        Azithromycin – less active against Staph & Strep. More active against respiratory pathogens – Hemophilus influenza, M catarrhalis. ↑resistance – Strep pneumoniae
        
        Telithromycin = azithromycin, but acts against resistant organisms
        
        Clarithromycin – Most active against intracellular pathogens – Chlamydia, Legionella, Moraxella, Mycoplasma, Ureaplasma, Helicobacter pylori
    - - MLS-B - methylase produced - affects Macrolides, Lincosamide, Streptogramin B
        
        Cross resistance complete between macrolides.
        
        ↓affinity of 50S ribosome in GP
        
        Plasmid mediated erythromycin esterase in GN
    - - Whooping cough - <2 months age - Azithro, >2 months - Clarithro (alternative drug - Co-trimoxazole)
        
        Azithromycin - 1) Chlamydial cervicitis/ urethritis – 1gm single dose
        2) Lymphogranuloma venereum, chancroid, Donovanosis
        3) Community Acquired Pneumonia (CAP) – 500mg loading dose, foll by 250mg for 4 days
        4) Legionnaire’s pneumonia – 500mg OD x 2 weeks
        
        Clarithromycin - 1) MAC (mycobacterium avium complex)
        2) H pylori
        3) atypical pneumonia (Chlamydia, Mycoplasma)
        
        Erythromycin - gastroparesis
        
        Fidoxamicin - pseudomembranous enterocolitis
        
        Spiramycin - Toxoplasma gondii in pregnancy
    - - GI distress & ↑motility - Esp with Erythromycin – motilin receptor agonist - Used in gastroparesis
        
        Cholestatic jaundice - max occurence with Esp with Erythromycin estolate, in pregnancy
        
        Deafness - Esp with ↑↑Erythromycin – transient, rarely Irreversible deafness with Azithro
        
        QTc Prolongation
        
        Infantile Hypertrophic Pyloric Stenosis in infants < 2 months age – Erythro & Clarithro