Mechanisms of Action of Antibiotics Flashcards
What are the 3 different mechanisms antibiotics can use to inhibit or kill bacteria?
- ) Inhibition of cell wall synthesis (e.g. penicillins & cephalosporins)
- ) Inhibition of Protein synthesis (e.g. gentamicin & erythromycin)
- ) Inhibition of nucleic acid synthesis (e.g. trimethoprim & ciprofloxacin)
What are the 2 types of beta-lactams?
Penicillins and cephalosporins
What do beta-lactams do?
- Disrupt peptidoglycan synthesis by inhibiting the enzymes which are responsible for cross-linking the carbohydrate chains.
INHIBIT CELL WALL SYNTHESIS
What are the enzymes which are involved in cell wall synthesis known as?
Penicillin-binding proteins
PBPs
Why are many gram negative organisms resistant to benzyl peniciliin?
Due to the relative impermeability of the gram negative cell wall.
What group do penicillins and cephalosporins belong too?
Beta-lactams
Why are human cells not disrupted by the action of beta-lactams?
They have no cell wall. Beta-lactams disrupt cell wall synthesis.
What are the 2 groups of antibiotics that inhibit cell wall synthesis?
- beta-lactams
- glycopeptides
What are the 2 glycopeptides in clincial use?
Vancomycin
Teicoplanin
What do vancomycin and telcoplanin (glycopeptides) do to kill or inhibit bacteria?
Inhibit assembly of peptidoglycan precursor
What type of bacteria do vancomycin and teicoplanin (glycopeptides) act on?
Gram positive bacteria only.
Why are vancomycin and teicoplanin (glycopeptides) usually only given parenterally?
They are not absorbed in the GI tract.
What is one of the negatives of Vancomycin use?
It is toxic.
Why must iv Vancomycin be given carefully?
If it leaks from the veins it can cause damage to the surrounding tissue.
Must be given enough to be theraputic but not too much as to be toxic.
What are some of the side effects of Vancomycin?
- Skin rash
- Ototoxicity
- Nephrotoxicity
What is ototoxicity and nephrotoxicity?
ototoxicity - toxic to ears
nephrotoxicity - toxic to the kidneys.
What are the antibiotics which are involves in the inhibition of protein synthesis?
- Aminoglycosides
- Macrolides & Tetracyclines
- Oxazolidinones
- Cyclic Lipopeptide
What types of bacteria can Aminoglycosides usually work on?
- Gram negative bacteria
- Most staphylococci
NOT streptococci
What is the most common aminoglycoside?
Gentamicin
What is the negative of gentamicin use?
Gentamicin is toxic, so it requires a careful dosing regime and monitoring of levels.
What are macrolides useful in?
Treatment of gram positive infections in patients that are allergic to penicillin.
What is a negative of macrolide use?
A signifiant percentage of staph. aureus, strep. ptogenes and strep. pnuemoniae strains are resistant. (This must be determined through testing).
What is the name of the common oxazolidinone?
Linezoid
What is linezoid useful in?
How is it given?
- Treatment of MRSA / serious infections
- Orally
What is the common cyclic lipopeptide?
Daptomycin
What is daptomycin used in?
Treating gram positives and MRSA/ serious infections.
What are the types of antibiotics which inhibit the synthesis of nucleic acids?
- Trimethoprim & sulphamethoxazole
- Fluoroquinolones
What do trimethoprim and sulphamethoxazole do to inhibit nucleic acid synthesis?
Inhibit steps in purine synthesis.
What are trimethoprim and sulphamethoxazole used in conjuction with?
co-trimoxazole
Why was the use of co-trimoxazole discouraged previously but is becoming more widely used now?
- Discouraged due to side effects
- Increase in use because it is less likely to cause C. diff infections than other broad spectrum agents.
What is Trimethoprim used to treat on its own?
UTIs
What is a common fluroroquinolones?
Ciprofloxacin
How does ciprofloxacin work?
How is it taken?
Direct inhibition of DNA synthesis
Orally and parenterally
What is ciprofloxacin useful against?
Gram negative organisms
When can ciprofloxacin not be used and why?
In treating children, due to the danger it could interfere with cartilage growth.
