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1
Antimicrobial Drugs
2
Antimicrobal Chemotherapy Terms
3
Chemotherapy
• The use of drugs to treat a disease
Early history of Antimicrobial Chemotherapeutic Agents
•Paul Ehrlich (1910) developed the concept of chemotherapy to treat microbial diseases
•
• He predicted the development of chemotherapeutic agents which would kill pathogens without harming the host
In 1930s Sulfa drugs came into prominenceGerhard Domagk
•Alexander Fleming discovered the first antibiotic penicillin in 1929
• ** its first trials were done in 1940
History of antibacterial•Paul Ehrlich articulates the principles of
chemotherapy in 1894•1910 introduce Salvarsan to treat syphilis
•Alexander Fleming discovered
• penicillin in 1929
•Penicillium spp
•.
•Synthetic antibiotic = sulfa drug
7
Antibiotic/Antimicrobial
• Antibiotic: Chemical produced by a microorganism that kills or inhibits the growth of another microorganism
• Antimicrobial agent: Chemical that kills or inhibits the growth of microorganisms
The Spectrum of antimicrobial Activity
•**it is easy to find or develop drugs that effective against prokaryotic cells ,& that do not affect the eukaryotic cells of humans
•**the problem is difficult when the pathogen is eukaryotic (fungus, protozoan, helminthes)
•**viral infection more difficult to treat
The Spectrum of antimicrobial Activity
•-**differ in cell wall•- differ in fine structure of their
ribosome•- details of their metabolism
•**resemble the human cell
•**the virus is within the human cells
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The
rape
utic
Inde
x• Selective toxicity: A drug that kills harmful
microbes without damaging the host
This is defined by Therapeutic Index as a measure of the degree of selective toxicity.
The therapeutic index is the ratio of the toxic dosage to the therapeutic dosage.
That is, (Lowest dose toxic to patient) (Dose normally used for therapy).
The greater the ratio (or difference) of these two numbers, the easier it is to find a dosage that kills the pathogen without harming the host.
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The
rape
utic
Inde
xTherapeutic Index = Toxic Dose/Therapeutic Dose
Dru
g D
osag
e (p
er K
g Bo
dy W
eigh
t)
Small Ratio(dangerous)
ModerateRatio
High Ratio(safe)
Most desirable.
12
Mechanisms of Antimicrobial Action
• Bacteria have their own enzymes for– Cell wall formation– Protein synthesis– DNA replication– plasma membrane– Synthesis of essential metabolites
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Tar
gets
of A
ntib
acte
rial D
rugs
14
Measuring Antimicrobial Sensitivity
• These tests are used to determine which chemotherapeutic agent is most likely to combat a specific pathogen
• These tests are used when susceptibility can not be predicted or when drug resistance arises
15
Susceptibility Tests
Agar diffusion = disk-diffusion test Kirby-Bauer Disk Diffusion Test
Sensitive
Intermediate
resistant
(cont’d)
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Antiviral Drugs
• Viruses are composed of nucleic acid, protein capsid, and host membrane containing virus proteins
• Viruses live inside host cells and use many host enzymes
• Some viruses have unique enzymes for DNA/RNA synthesis or protein cutting in virus assembly
• Viruses are reproduce only inside living cells
Viral replicative cycle
• Attachment === receptors• Penetration
• Uncoating• Nucleic acid replication
•( polymerases )
• Assembly• Release
Antiviral drugs•Inhibitors of
• Attachment• Penetration
• Uncoating• Nucleic acid synthesis
•( polymerases inhibitors)• Assembly
• Release
Antifungal Drugs
•Inhibitors of
• cell wall synthesis
• plasma membrane = sterols = ergosterol
interfere with RNA biosynthesis
Anti parasitic drugs•Anti protozoan & anti helminthes drugs
• Inhibit enzymes and proteins
• Inhibit nucleic acid synthesis
• Inhibit nutrient absorbtion
• Alters membrane permeability
• Prevent ATP generation