antimicrobial drugs au10
TRANSCRIPT
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Antimicrobial Drugs
Chapter 20
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Antimicrobial Drugs
Antimicrobial drugs: Interfere with the growthof microbes within a host
Antibiotic: A substance produced by a microbethat, in small amounts, inhibits another microbe
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1928: Flemingdiscovered
penicillin,
produced byPenicillium
1940: Howard
Florey and ErnstChain performed
first clinical trials
of penicillin
Antimicrobial Drugs
Figure 1.5
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Features of Antimicrobial Drugs
1. Selective toxicity
2. Antimicrobial action:
Bac
te
r ios
tatic
vs.
Bac
te
r ic
idal3. Spectrum of activity:
Broad-spectrum vs. Narrow-spectrum
4.
Adverseeffects: Allergies,
Toxicity,
Suppression of the normal flora
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Mechanism of Action of
Antibacterial drugsTargets :
Inhibition of cell wall synthesis
Inhibition of protein synthesis
Inhibition of nucleic acid synthesis
Inhibition of me
tabolic
pathways
Inhibition of cell membrane integrity
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The Action of Antimicrobial Drugs
Figure 20.2
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1. Inhibitors of Cell Wall Synthesis
Penicillin1. Natural penicillins
Penicillin G and Penicillin V
2. Semisynthetic penicillins
Extended-spectrum penicillins
Res
is
tant to Pe
nic
illinase/
-Lac
tamase
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Figure 20.6
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2. The Inhibi tion of Protein Synthesis by Antibiotics
Figure 20.4
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Antibiotic Resistance
A variety of mutationscan lead to antibioticresistance
Resistance genes are often on plasmids ortransposons that can be transfer red betweenbacter ia
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Resistance to Antibiotics
Figure 20.20
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Selective advantage
Figure 21.13
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Antibiotic Resistance
Misuse of antibioticsselects for resistancemutants. Misuse includes
Using outdated or weakened antibiotics
Using antibiotics for thecommon cold and otherinappropriateconditions
Using antibiotics in animal feed
Failing to complete the prescr ibed regimen
Using someoneelse's leftover prescription
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Examples of emerging resistance
1. Enterococci (vancomycin resistantenterococci)
2. Staphylococcusaureus(methicillin resistant Staphylococcusaureus)
3. Streptococcuspneumoniae(penicillin
resistant)4. Mycobacteriumtuberculosis
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Effects of Combinations of Drugs
Synergism occurs when the effect of twodrugs together is greater than the effect of
either alone
Antagonism occurs when the effect of twodrugs together is less than the effect of either
alone
Antibiotic SafetyTherapeutic index: risk vs. benefit
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Anti-viral drugs
Selective toxicity difficult to achieve
Antibiotics (antibacterials) have no effect
on viruses
Relatively few
Nonecan eliminate latent viruses
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Targets
Unc
oatingAmantadine & rimantidine influenza
Nucleic acid synthesis
Nuc
le
os
ide
analogs
He
rpes
virus
& HI Vpolymerase inhibitors
Assembly and release
Prote
ase
inhibitors
H I VNeuraminidase inhibitors - influenza
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Nucleoside and Nucleotide Analogs
Figure 20.16b ,c