Antimicrobial Chemotherapy Flashcards
What is therapeutic index?
Ratio of toxic dose to the therapeutic dose (eliminates infection) - the larger the index the safer the drug is
Characteristics of antibiotic
Wide spectrum activity Nontoxic and nonallergic No undesirable side effect Shouldn't eliminate normal flora Able to reach source infection Inexpensive and easy to produce Chemically stable Microbial resistance
What is MIC and MBC
MIC - minimal inhibitor concentrate - min [antimicrobial] needed to inhibit growth
MBC - minimal bactericidal conc. min [] needed to kill
What are targets for antimicrobials?
Cell wall Protein synthesis Metabolic pathway DNA Membrane Enzymes
What is penicillin
Beta-lactam - bactericida compound
How to beta-lactam work?
Beta-lactam ring inhibit cell wall formation by inhibit peptidoglycan formation
Example beta-lactam
Penicillin - 5 membered
Cephalopsorin - 6 membered
How does penicillin work?
Mimic D-ala D-ala
Inhibit formation peptidoglycan cross link in bacterial cell wall by binding beta-lactam ring to enzyme DD-transpeptidase
Enzyme can’t catalyse cross link = cell death
Use of vancomycin and how it works?
Effective gram +ve
Bind D-ala D-alanine on newly synthesised peptidoglycan - prevent incorporation into cell wall
What antimicrobial effect protein synthesis?
Erythromycin, tetra cline, aminoglycosides, fusic acid
How does erythromycin work?
Bind to 50s subunit block exit nascent polypeptide chains
How do tetracyclines work?
Inhibit binding tRNA to mRNA
Incorporated developing bones and teeth
How to aminoglycosides work?
Bind 30s subunit - misreading genetic code
Effective against aerobes and facultative anaerobes
How does fusic acid work
Bind EGF - prevent protein synthesis
Why are ahminoglycosides not effective against anaerobes?
Bacterial take up requires oxygen - dependent electron transport
What is a macrolide?
Bacteriostatic compound w/ macrocyclic lactone ring e.g erythromycin (used for those w/ penicillin allergy)
Example DNA affected microbial?
Rifamycins, metronidzaole
How does metroinidazole work?
Disrupt DNA - only effect against anaerobes
Activated in cells via REDOX enzyme (ferredoxin is e- transporter molecule)
Electron transfer creates anion - disrupt DNA helix
What is Antimicrobial resistance?
An organism that is not inhibited or killed by antibacterial agent at [] achievable by drug at normal dose
How is antimicrobial resistance caused?
- Chromosomally- mediated resistance - mutant selecting
- Plasmid - mediated - spread of resistant plasmid
- Plasmid-mediate resistance on transpoon - spread of resistant gene
Antimicrobial resistance - how it doesn’t work
- Target structurally altered
- target overproduced
- drug is not activated
- drug is removed
How does antiviral work? - are they common?
No - few in number and narrow spec
Need to interfere w/ viral machinery w/o affecting host
