AM - Definitions and Mechanisms Flashcards
What is Bactericidal?
Antimicrobial that kills bacteria
What is Bacteriostatic?
Antimicrobial that inhibits the growth of bacteria
Define sensitive
Organism is sensitive if it is inhibited or killed by the antimicrobial at the site of infection
Define resistant
Organism is resistant if it is not killed or inhibited by the antimicrobial needed to kill a given organism
Define Minimal Bactericidal Concenration
MBC is the minimum concentration of antimicrobial needed o kill a given organism
Define Minimal inhibitory concentration
MIC is the minimum concentration of antimicrobial needed to inhibit growth of a given organism
What are the routes of administration of antibiotics?
- Topical
- Systemic
- Parenteral
Describe the topical route of administration of antibiotics.
Applied to surface e.g. skin or mucous membrane
Describe the systemic route of administration of antibiotics
Taken internally (orally or parenterally)
Describe the parenteral route of administration of antibiotics
- Administrated intra-venously (IV) or intra-muscularly (IM)
- Occasionally sub-cutaneously
What are the mechanisms of action of antibiotics?
- Inhibition of cell wall synthesis
- Inhibiton of protein synthesis
- Inhibition of nuclei acid synthesis
How does inhibition of cell wall synthesis work?
Disrupt peptidoglycan synthesis by inhibiting the enzymes (penicillin-binding proteins, PBPs), responsible for cross-linking the carbohydrate chains.
Features of inhibition of cell wall synthesis
- Penicillins and Cephalosporins
- beta-lactam ring antibiitics
- bactericidal antibiotics
- effective mostly against gram-positive bacteria
Describe benzyl penicillin
Many gram negative organisms are resistant against benzyl pencillin
What is another type of inhibition of cell wall synthesis?
-Glycopeptides
What do glycopeptides do?
- They have an inability to penetrate the gram negative cell wall and act only on gram positive organisms too
- not absorbed from the GI tract and are only given parenterally
What are examples of glycopeptides?
Vancomycin and teicoplanin
- toxicity Is very common in vancomycin. Careful IV infusion in order to avoid local tissue damage, and ensure the concentration is high enough to be therapeutic but not toxic.
- Teicoplanin is less toxic than vancomycin and has the advantage of single daily dosing
How does inhibition of protein synthesis work?
- Works by binding to the bacteria’s ribosomes.
- This prevents the tRNA from landing and adding its amino acid onto the growing protein
Which antibiotics inhibit protein synthesis?
- Aminoglycosides
- Macrolides
- Tetracyclines
- Oxazolidinones
- Cyclic lipopeptide
What do Aminoglycosides do in inhibiting protein synthesis?
example?
- concentration depended bactericidal antibiotics
- useful in the treatment of serious gram negative infection (eg coliform)
- e.g. Gentamicin. It is toxic and requires a careful dosing regime and monitoring of levels
What do Macrolides do in inhibiting protein synthesis?
example?
- Concentration dependent bacterial, bactericidal, or bacteriostatic antibiotics
- Useful alternative to penicillins in treatment of Gram-positive infection in patients
- E.g. Erythromycin
What do tetracyclines, oxazolidinone, cyclic lipopeptide do?
Treat gram-positive infections
How does inhibition of nucleic acid synthesis work?
- Inhibit DNA synthesis directly or indirectly by interrupting the supply of precursors for DNA synthesis
- used orally as well as parenterally
- cannot be used in children (interference with cartilage growth)
Which antibiotics inhibit nucleic acid synthesis?
Trimethoprim and fluoroquinolones
What is inhibition of nucleic acid synthesis effective against?
Gram-negative organisms, including Pseudomonas
What antibiotics inhibit cell wall synthesis?
Penicillins
Cephasporins
Glycopeptides
