Antibiotics

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  • Antibiotics
    • Beta-lactam antibiotics
      • Penicillin G
        • Formed first, not stable under acidic conditions - Fleming
      • Penicillin V
        • Introduced oxygen into structure, now acid stable so can be taken orally - Florey and Chain
      • Semi-synthetic penicillin
        • Amoxicillin (made from Pen V) Methicillin (made from Pen G)
      • Clinical usage
        • URTI (eg. tonsillitis) LRTI (eg. pneumonia) STI (eg. gonorrhoea, syphilis)   Skin and tissue infections
      • Mechanism of action
        • They stop peptidoglycan linkage by inhibiting transpeptidases and activate autolysinsIf they get into the bacteria, they are Bactericidal. Competitive inhibition and irreversible binding
    • Quinolones
      • Mechanism of action
        • Quinolone antibiotics interfere with changes in DNA supercoiling by binding to DNA gyrase (topoisomerase II [1st and 2nd generation Qs] or topoisomerase IV [3rd and 4th generation Qs]). This prevents DNA unzipping and leads to ds DNA breaks and cell death
      • Examples
        • Ciprofloxacin LevofloxacinMoxifloxacin
      • 24% world's manufactured antibiotics, synthetic antibacterial compounds. Found in all bacteria therefore broad spectrum (G+/-). Derivatives of nalidixic acid (fluorinated) Quinoline backbone Variety of functional R-group, overcomes resistance, improves reaction etc Has two benzene rings
      • Clinical usage
        • UTIs        MDR (multi-drug resistance bacterial) Infections PyelonephritisProstatitis Pneumonia  Highly restricted use in children in UK (anthrax or cystic fibrosis pulmonary infection) - musculoskeletal side effects
    • Macrolides
      • Natural products (polyketides) 20% world's manufactured antibiotics  Macrocyclic lactone ring - core      Mostly G+ (limited G-) considered broad spectrum Most active against G+ cocci (mainly staphylococci and streptococci) Also active against Mycobacteria, Mycoplasma, Ureaplasma, spirochetes, and other organisms.
      • Mechanism of action
        • Inhibit progression of protein synthesis by reversibly binding to P site on 50C ribosomal subunit. Depending on concentration they are either bactericidal or bacteriostatic
      • Examples
        • ErythromycinAzithromycinClarithromycin Roxithromycin
      • Clinical usage
        • Gram positive infections (e.g. Streptococci)MycobacteriaGram negative infections (e.g. Bordetella pertussis)
    • Aminoglycosides
      • Examples
        • Gentamycin (used for drug resistant infections) Tobramycin Amikacin
      • MOA
        • Protein synthesis inhibitors - bind to the aminoacyl site of 16S rRNA in 30S subunit of the ribosome (irreversible).Cause mis-incorporation of amino acids into elongating peptides. Incorporation of misfolded membrane proteins into the cell envelope leads to increased drug uptake - leaky walls. Increase in ribosome binding = cell death
      • Clinical usage
        • Use for antibiotic resistant G- infectionsIncorporated into combination for G+Issues with nephrotoxicity and ototoxicityMycobacterium tuberculosis, NTM and Neisseria gonorrhoeae
      • Streptomycin from Streptomyces griseus Bactericidal (aerobic G-) Mostly G- bacteria [not anaerobes] (+ Mycobacteria)
    • Tetracyclines
      • MOA
        • Protein synthesis inhibitors - inhibit binding of aminoacyl-tRNA to mRNA-ribosome complex in the A site of 30S ribosomal subunit. Stall protein synthesis, reversible binding. Cause disruption to proteome leading to bactiostasis, also bind matrix metalloproteinases
      • Examples
        • Tetracycline Doxycycline Minocycline
      • Broad spectrum (better against G+) Derivatives of polycyclic naphthacene carboxamide
      • Clinical usage
        • UTI  U/LRTIGI Tract infections Chlamydia (if allergic to ?-lac or macrolides) Acne Rickettsia Brucellosis Spirochetal infections (syphilis and Lyme disease (borreliosis)) Anthrax, plague, Legionnaires' disease Cholera

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