LecturePP7&8Antibiotics

LecturePP7&8Antibiotics - Chemotherapy of Bacterial...

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Chemotherapy of Bacterial Infections ~~~~~~~~ Antibiotics
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Definitions of Antibiotics OLD : An antibiotic is a chemical substance produced by various species of microorganisms that is capable in small concentrations of inhibiting the growth of other microorganisms NEW: An antibiotic is a product produced by a microorganism or a similar substance produced wholly or partially by chemical synthesis, which in low concentrations, inhibits the growth of other microorganisms
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Impact of Modern Healthcare on Life Expectancy
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History Paul Ehrlich “Magic Bullet” Chemicals with selective toxicity ORIGIN : Selective Stains DRUG : Arsphenamine (1910) “606” Salvarsan NOBEL : 1908
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History (cont’d) Gerhard Domagk Drugs are changed in the body ORIGIN : Prontosil (Only active in vivo ) DRUG : Sulfanilamide (1935) NOBEL: 1939
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History Alexander Fleming Microbes make antibiotics ORIGIN : moldy culture plate DRUG : Penicillin (1928) NOBEL: 1945 (cont’d)
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History (cont’d) Selman Waksman Soil Streptomyces make antibiotics comes up with definition of antibiotic ORIGIN : Penicillin development DRUG : Streptomycin (1943) NOBEL: 1952
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The Ideal Drug* 1. Selective toxicity: against target pathogen but not against host LD 50 (high) vs. MIC and/or MBC (low) 1. Bactericidal vs. bacteriostatic 2. Favorable pharmacokinetics: reach target site in body with effective concentration 3. Spectrum of activity: broad vs. narrow 4. Lack of “side effects” Therapeutic index: effective to toxic dose ratio 1. Little resistance development * There is no perfect drug .
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Antibacterial spectrum Range of activity of an antimicrobial against bacteria. A broad-spectrum antibacterial drug can inhibit a wide variety of gram-positive and gram-negative bacteria, whereas a narrow-spectrum drug is active only against a limited variety of bacteria. Bacteriostatic activity —- The level of antimicro-bial activity that inhibits the growth of an organism. This is determined in vitro by testing a standardized concentration of organisms against a series of antimicrobial dilutions. The lowest concentration that inhibits the growth of the organism is referred to as the minimum inhibitory concentration (MIC). Bactericidal activity The level of antimicrobial activity that kills the test organism. This is determined in vitro by exposing a standardized concentration of organisms to a series of antimicrobial dilutions. The lowest concentration that kills 99.9% of the population is referred to as the minimum bactericidal concentration (MBC). Antibiotic combinations Combinations of antibiotics that may be used (1) to broaden the antibacterial spectrum for empiric therapy or the treatment of polymicrobial infections, (2) to prevent the emergence of resistant organisms during therapy, and (3) to achieve a synergistic killing effect. Antibiotic
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This note was uploaded on 10/21/2011 for the course BIO 1162 taught by Professor Howard during the Fall '11 term at UMSL.

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LecturePP7&8Antibiotics - Chemotherapy of Bacterial...

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