Principles of Antimicrobial Chemotherapy Flashcards
Define chemotherapy.
The use of chemicals, natural or synthetic, to inhibit the growth and replication of invading organisms or cancer cells within the body.
Define selective toxicity.
1- Agents which are toxic to invading organisms or cancerous cells, but relatively harmless to the host of normal cells
2- This approach depends on the existence of biochemical differences between target cells and host cells
What five drug classes are active against the cell membrane?
1- β-lactam and cephalosporin 2- Glycopeptide 3- Cyclic peptide 4- Phosphonic acids 5- Lipopeptide
What drug class is penicillin G?
β-lactam
Where are peptidoglycans found?
1- Cell walls
2- Do not occur in eukaryotes
Describe the features of peptidoglycans.
1- Strands are made of of multiples of amino-sugars: N-acetylglucosamine and N-acetylmuramic acid dimers.
2- N-acetylmuramic acid has a short peptide side chain
3- Peptide side chains cross-link to form a latticework which provides strength
4- Found in bacteria cell walls
How do β-lactams, such as penicillin G, act on bacteria?
Prevent peptidoglycan cross-linking in cell wall
What are the two first generation penicillins?
1- Penicillin G
2- Penicillin V
What are the five β-lactamase-resistant penicillins?
1- Methicillin 2- Oxacillin 3- Nafcillin 4- Cloxacillin 5- Dicloxacillin
What are two broad-spectrum penicillins?
1- Ampicillin
2- Amoxicillin
What are four extended-spectrum penicillins?
1- Carbenicillin
2- Ticaracillin
3- Azlocillin
4- Piperacillin
Where are cephalosporins derived from?
From the fungus Cephalosporium acremonium
What is the mechanism of cephalosporins?
Prevent cross-linking of peptidoglycans in cell wall
What is cephalexin?
1- Cephalosporin
2- Oral intake
What is cefuroxime?
1- Cephalosporin
2- Parenteral intake
What is cefotaxime?
1- Cephalosporin
2- Parenteral intake
What are two examples of antibiotics that inhibit the folate pathway in bacteria?
1- Sulphonamides
2- Trimethoprim
What is the mechanism of sulphonamides?
1- Selective toxicity
2- Inhibit folate pathway in bacteria
3- Inhibit dihydropteroate synthetase enzyme
What is the mechanism of trimethoprim?
1- Selective toxicity
2- Inhibits folate pathway in bacteria
3- Inhibits dihydrofolate reductase enzyme
What are four examples of aminoglycosides?
1- Streptomycin
2- Kanamycin
3- Neomycin
4- Gentamycin
What is the mechanism of aminglycosides?
1- Form ionic bonds at the cell surface
2- Penetrate cell wall and cell membrane
3- Diffuse into cytoplasm
4- Bind to bacterial ribosomes either at the interface between the assembled 30s and 50s subunits or directly to individual subunits
5- Inhibit protein synthesis by causing ribosomes to misread mRNA
What is the mechanism of tetracyclines?
1- Prevent attachment of tRNA to A site on the mRNA-ribosomal complex
2- This prevents the addition of new amino acids to the growing peptide chain
What determines the difference in activity between different tetracyclines?
What determines the difference in activity between different tetracyclines?
What is the mechanism of chloramphenicol?
1- Binds to ribosomes
2- Prevents addition of new amino acids to growing peptide chain
3- Prevents association of peptidyl-transferase to amino acid, thus preventing formation of peptide bond
What is the mechanism of erythromycin?
1- Binds to ribosomes
2- Prevents addition of new amino acids to growing peptide chain
3- Prevents translocation of ribosomes down the mRNA chain
What is the mechanism of clindamycin?
1- Binds to ribosomes
2- Prevents addition of new amino acids to growing peptide chain
3- Prevents association of peptidyl-transferase to amino acid, thus peptide bond cannot be formed
Where are fluoroquinolones derived from?
Synthetically
What are three examples of broad-spectrum fluoroquinolones?
1- Ciprofloxacin
2- Ofloxacin
3- Norfloxacin
What are two examples of narrow-spectrum fluoroquinolones?
1- Cinoxacin
2- Nalidixic acid
What is the mechanism of fluoroquinolones?
1- Inhibit bacteria DNA Topoisomerase II (DNA gyrase)
2- Transcription and translation not carried out
