2. antibiotics leture 2, 3, 4.pptx - PHARMACOLOGY III ANTIBIOTICS 1-8 Objectives… • At the end of this lecture each student should be able to List

2. antibiotics leture 2, 3, 4.pptx - PHARMACOLOGY III...

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Objectives… At the end of this lecture each student should be able to; List the classes of antibiotics, and describe their mechanisms of action, therapeutic uses, and adverse effects. Outline mechanism of development of bacterial drug resistance Describe the factors in choosing appropriate antibiotic agents
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Classification Antimicrobials Antibacterial Antifungal Antiviral Antiparasitic Antiprotozoal Anthelmintic Anticancer (Cytotoxic) Disinfectants, Antiseptics, Sterilants
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Basis for Classification of Antibiotics Chemical Structure e.g. beta-lactams aminoglycosides tetracyclines Specific Targets on the organism e.g. cell wall synthesis inhibitors protein synthesis inhibitors Nucleic acid (DNA & RNA) synthesis inhibitors
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Bacterial Targets for Antibiotics
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Beta-lactam antibiotics 1. Penicillins 2. Cephalosporins 3. Carbapenems 4. Monobactams
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Classification of Penicillins 1. Natural penc. The prototype Penicillin G Acid resistant Penicillin V 2. “Extended Spectrum” Amoxicillin, Ampicillin 3. “Antipseudomonal” ticarcillin, Piperacillin 4. Antistaphylococcal methicillin, nafcillin, oxacillin, dicloxacillin Penicillinase resistant Methicillin, Oxacillin Combinations (Penicillin + b -lactamase
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Mechanism of action of penicillins Inhibit bacterial cell wall synthesis Bind to penicillin binding proteins (PBPs) Inhibit transpeptidases (form cross-links in peptidoglycan) Cross-linking is reduced Bactericidal inhibitors
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Pharmacokinetics of penicillins Absorption: can be oral Stability in acid condition: PenG (no) Pen V (yes) Ampicillin (yes) -Incompletely absorbed orally. -Food decreases absorption due acid. Distribution : to most body sites; not in CSF and bone unless inflamed, also insufficient prostate levels. Excretion: rapidly eliminated by renal tubular secretion. Except for nafcillin and oxacillin which are metabolised in the liver. Amoxacillin (yes) Nafcillin (yes) Piperacillin (no)
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SPECTRUM OF PENICILLINS Natural Penicillins Penicillin G Benzathine PN G Procaine PN G Penicillin V Streptococcus Neisseria meningitidis Spirochetes Penicillinase-resistant Methicillin Oxacillin Nafcillin Cloxacillin Dicloxacillin Staphylococcus aureus Aminopenicillins Ampicillin Amoxicillin Heamophilus influenzae Proteus mirabilis E. coli Neisseria Carboxypenicillins Carbenicillin Ticarcillin Pseudomonas Enterobacter Proteus Ureidopenicillins Piperacillin Azlocillin Mezlocillin Pseudomonas Enterobacter Klebsiella
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Clinical Uses of Penicillins Pen G (Pen V): natural Common streptococci ( S. pneumoniae; S. pyrogenes ); URTI, pneumonia meningitis, prophylaxis of rheumatic fever Nafcillin: penicillinase-resistant Staphylococci epidemic; bacteremia, septicemia Ampicillin, Amoxycillin: Gram- spectrum: E. coli; H. influenzae;Salmonella, shigella pharyngitis, otitis media, UTI, gastroenteritis Piperacillin:
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