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INTRODUCTION TO ANTIBIOTICS - MICRO {ST1}

INTRODUCTION TO ANTIBIOTICS - MICRO {ST1}. BY RANJEET RAMAN. Drugs separated by mechanism of action, spectrum of activity, adverse effects, selective toxicity.

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INTRODUCTION TO ANTIBIOTICS - MICRO {ST1}

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  1. INTRODUCTION TO ANTIBIOTICS - MICRO {ST1} BY RANJEET RAMAN

  2. Drugs separated by mechanism of action, spectrum of activity, adverse effects, selective toxicity. An antibiotics is a substance produced by bacteria, fungi, or actinomycetes, that has the capacity ​to inhibit the growth or destroy bacteria and other microorganisms.

  3. Within a class, know antibiotics by incremental coverage. Group organisms with similar drug ​sensitivities, and know organisms for their clinical syndromes. It is best to use the ​narrowest spectrum of coverage to avoid resistance and adverse effects.

  4. Therapeutic index = LD50/ED50 = MTD/MED is very high for antibiotics. Host efficacy = Bacterial toxicity – Host toxicity

  5. Bactericidal = kills bugs Bacteriostatic + healthy immune system and good penetration = kills bugs Bacteriostatic = stops bugs

  6. Bactericidal Bacteriostatic Penicillins Tetracycline Cephalosporins Macrolides Quinolones Chloramphenicol Aminoglycosides Clindamycin Trimethoprim + Sulfamethoxazole Trimethoprim or Sulfonamides alone

  7. Synergistic and Antagonistic effects of using two drugs at once. Tissue penetration can be a problem due to molecular size, protein binding, but especially ​inflammation. During inflam, membrane transporters may become poisoned, keeping ​drugs within cells longer. Thus, many ABX work better in the setting of inflammation.

  8. Penetrating the bacteria is also difficult. They have outer membranes (Gram- only), periplasmic ​β-lactamases, and cytoplasmic pumps. They can also gain resistance by: ​modifying drug target or the drug itself ​--bypassing the inhibited reaction ​--overproducing the target enzyme ​--activating efflux pumps

  9. Post-Antibiotic Effect (PAE) Suppression of bacterial growth persisting after short exposure to ABX agent. Even after drug is ​totally gone, bacteria keep declining. β-lactam ABX exhibit PAE against Gram+ but not Gram- bacteria. Aminoglycosides and quinolones exhibit PAE against Gram- bacteria.

  10. Time-dependent versus Concentration-dependent effects For some drugs, such as aminoglycosides, killing increases with concentration. With other drugs, ​such as β-lactam drugs, killing does not increase as concentration rises above the MIC. For ​these drugs you’d simply dose at the MIC.

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