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Antibiotics basic


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Antibiotics basic

  1. 1. ANTIBIOTICS Antibiotics are obtained from Fungi penicillins,cephalosporin,griseofulvin Bacteria polymyxin B,Tyrothricin colistin,aztreonam,bacitracin Actinomycetes aminoglycosides,macrolides,tetracyclines polyenes,chloramphenicol
  2. 2. CLASSIFICATION- A) Chemical structure Β-lactam antibiotics- penicillins,cephalosporins,monobactams,carbapenems Tetracyclins Oxytetracycline,doxytetracycline Nitrobenzene derivative- chloramphenicol Aminoglycosides Streptomycin,gentamycin,amikacin,neomycin
  3. 3. Macrolide antibiotics Erythromycin,clarithromycin,azithromycin Glycopeptide antibiotics Vancomycin,teicoplanin Lincosamide antibiotics Lincomycin,clindamycin Oxazolidinone- linezolid
  4. 4. Polypeptide antibiotics Polymyxin-B, colistin,bacitracin Polyene antibiotics Nystatin,amphotericin-B B. Mechanism of action 1. Inhibit cell wall synthesis penicillins,cephalosporins,cycloserines vancomycin,bacitracin
  5. 5. 2. Causes leakage from cell wall membrane Polypeptide-polymyxins,colistin,bacitracin Polyenes- amphotericin B,nystatin 3. Inhibit protein syntheis tetracyclins,chloramphenicol,erythromycin, clindamycin 4. Cause misreading of m-RNA code and affect permeability Aminoglycosides-streptomycin,gentamycin
  6. 6. SPECTRUM OF ACTIVITY Narrow spectrum penicillin G streptomycin erythromycin Broad spectrum tetracyclines chloramphenicol
  7. 7. PENICILLINS First antibiotic to be used clinically in 1941 Originally obtained from fungus Penicillium notatum Present source is a high yeilding mutant of P. chrysogenum
  8. 8. CHEMISTRY AND PROPERTIES 1- Thiazolidine ring 2- β-lactam ring CH C CH3 CH3 CH S C NH COOHC N O O R 12 Benzyl side chain PENICILLINS Amide linkage
  9. 9. MECHANISM OF ACTION - Inhibit transpeptidase so that cross linking does not take place -When bacteria divide in presence of β-lactam antibiotics –cell wall deficient(CWD) forms are produced -because the interior of the bacterium is hyperosmotic ,the CWD forms swell & burst bacterial lysis
  10. 10. Lytic effect of these antibiotics may also be due to derepression of some bacterial autolysins which normally function during cell division Penicillin G Spectrum- narrow active only against gram +ve bacteria Cocci: Streptococci,Pneumococci gram –ve cocci- Neisseria gonorrhoeae N.meningitidis
  11. 11. Bacilli: gram +ve - Corynebacterium. Dephtheriae clostridia tetani garm –ve- Actinomyces israelii BACTERIAL RESISTANCE Many bacteria are inherently insensitive to PnG Because in them the target enzyme & PBPs are located deeper under lipoprotein barrier wher PnG is unable to penetrate
  12. 12. Production of penicillinase it is a narrow spectrum β-lactamase which opens the β-lactam ring and inactivates PnG. Some bacteria become Penicillin tolerant –their target Enzymes are altered to have low affinity for penicillin Gram –ve bacteria have porin channels located in their outer membrane.some gram –ve bacteria become resistant By loss or alteration of porin channels.
  13. 13. PHARMACOKINETICS A- PnG is acid labile-destroyed by gastric acid absorption from i.m route is rapid & complete D – Reaches most of the body fluids Penetration in CSF is poor M- Little metabolised because of rapid excretion E- Very rapid renal excretion
  14. 14. ADVERSE EFFECTS Local irritancy and direct toxicity pain at i.m injection site nausea on oral ingestion Larger dose injected i.v – Mental confusion Muscular twitching convulsions,coma. Hypersensitivity rash,itching & fever
  15. 15. USES 1.Streptococcal infections 2. Pneumococcal infections 3.Meningococcal infections 4.Gonorrhoea 5.Syphilis 6. Diphtheria 7.Tetanus
  16. 16. 8.Drug of choice for rare infections like anthrax,rat bite fever,trench mouth SEMISYNTHETIC PENICILLINS Shortcomings of PnG -Poor oral efficacy -Suseptibility to penicillinase -Narrow spectrum of activity -Hypersensitivity reactions
  17. 17. CLASSIFICATION 1.Acid resistant alternative to PnG phenoxymethyl penicillin(Penicillin V) 2.Penicillinase-resistant penicillins methicillin,cloxacillin 3.Extended spectrum penicillins a) aminopenicillins: ampicillin.bacampicillin,amoxicillin b) carboxypenicillins: carbenicillin,ticarcillin c) ureidopenicillins: piperacillin,mezlocillin β-lactamase inhibitors Clavulanic acid,sulbactum,tazobactum
  18. 18. 1.Acid resistant alternative to PnG -acid stable -oral absorption better -antibacterial spectrum identical to PnG -but it is1/5 as active against Neisseria 2.Penicillinase-resistant penicillins -these have side chains that protect the β-lactam ring from attack by staphylococcal penicillinase Methecillin- penicillinase resistant but not acid resistant
  19. 19. Cloxacillin- Highly penicillinase resistant as well as acid resistant 3. Extended spectrum penicillins Effective against gram-ve bacilli 1.Aminopenicillins -These have amino group in side chain -prodrugs -none is resistant to penicillinase
  20. 20. AMPICILLIN Uses -UTI -RTI -Meningitis -Gonorrhoea BACAMPICILLIN Ester prodrug of ampicillin Completely absorbed from g.i.t AMOXICILLIN Close congener of ampicillin Not a prodrug Oral absorption is better
  21. 21. 2. CARBOXYPENICILLINS -active against pseudomonas aeruginosa & proteus - Carbenicillin is neither penicillinase resistant nor acid resistant -inactive orally 3.UREDOPENICILLINS Piperacillin -8 times more active than carbenicillin -used mainly in immunocompromised patients having serious gram-ve infections
  22. 22. BETA-LACTAMASE INHIBITORS Clavulanic acid Obtained from streptomyces clavuligerus Has β lactam ring but no antibacterial activity