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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Using outdated or weakened antibiotics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