Antibiotic Classes Flashcards
Name the different mechanisms of action of antibiotics?
- Inhibit cell wall synthesis
- Inhibit protein synthesis
- Interfere with DNA synthesis
- Disrupts cell membrane
Name the 3 groups of cell wall synthesis inhibitors?
- Beta-lactams (penicillins, cephalosporins, carbapanems)
- Glycopeptides (e.g. vancomycin)
- Isonazid
Name the 3 types of Beta-lactams?
Penicillins, Cephalosporins, Carbapanems
Are B-lactams bactericidal or bacteriostatic?
Bactericidal
What is the mode of action of B-lactam antibiotics?
B-lactams act against bacteria by inhibiting the synthesis of the peptidoglycan layer in the bacterial cell walls.
The B-lactam ring structure is capable of binding to the enzymes with cross-link the peptidoglycan layers (transpeptidase/penicillin-binding proteins).
The result: damage to cell. gram-positive bacteria have high osmotic pressure, without a rigid cell wall, the cells burst when subjected to the low osmotic pressure of their surrounding environment.
Peptidoglycan is a polymer of what?
NAM (N-acetyl muramic acid)
NAG (N-acetyl glucosamine)
Summarise the process of peptidoglycan synthesis
- NAG is added to NAM to form a precursor of peptidoglycan
- Precursor transported across the cell membrane
- Precursors undergo cross-linking to create cell wall (x2 major enzymes involved: transpeptidases (aka penicillin-binding proteins)
What is the basic mechanism of B-lactam resistance?
alteration of the penicillin binding proteins
and
beta-lactamase
Action of beta-lactamase enzymes? how is this overcome clinically?
Bacteria produce enzymes called beta-lactamases in an attempt to overcome the action of the antibiotics. The b-lactamases break open the beta lactam ring, rendering inactive.
overcome clinically: b-lactamase inhibitors
Give an example of beta-lactamase inhibitor? How does it work?
Clavulanic Acid
has a similar structure to antibiotic, beta-lactam ring
blocks the active site of the beta lactamases to prevent them from destroying the antibiotic
Give an example of an antibiotic + inhibitor combination?
Amoxicillin + Clavulanic Acid
= Co-amoxiclav
What is the mechanism of the glycopeptide antibiotics?
glycopeptides also inhibit cell wall synthesis.
BUT bind directly to the side-chains, rather than the transpeptidases/PBPs.
result = PBPs can’t access the side chains
When might a glycopeptide be preferential over a beta-lactam antibiotic?
In cases of MRSA - resistance.
(MRSA - flucloxacillin resistant form of s.aureus)
against MRSA, glycopeptides would still work, for example: Vancomycin
Example of a Carbapenem?
Meropenem
What time of bacteria is vancomycin best to use against?
gram(+) - cell wall, peptidoglycan
virtually ineffective against gram(-)
What are the 3 groups of protein synthesis inhibitors?
- Macrolides
- Aminoglycosides
- Tetracyclines
What is the mode of action of the protein synthesis inhibitors?
bind to the ribosome and block translation (no amino acid chain forms)
target either 30s or 50s sub-unit
Which antibiotic group targets the 50s sub-unit of the ribosome?
Macrolides
Which antibiotic group targets the 30s sub-unit of the ribosome?
Aminoglycosides
Tetracyclines
Name the 3 antibiotic groups that interfere with DNA synthesis/replication?
- Sulphonamides
- Diaminopyrimidines
- Quinolones
What is the mechanism of action of the sulphonamides?
they block nucleotide synthesis!
bacteria can’t absorb folate like human cells, have to synthesise it - they are folate synthesis inhibitors
block enzyme at earlier stage of infection
What is the mechanism of action of the Diaminopyramidines?
they block nucleotide synthesis!
bacteria can’t absorb folate like human cells, have to synthesise it - they are folate synthesis inhibitors
blocks enzyme at later stage of infection
Example of a Diaminopyramidine antibiotic?
Trimethoprim
What is the mechanism of action of the Quinolones?
DNA gyrase inhibitor
stops the DNA unwinding before replication
rapidly fatal!
Example of a Quinolone?
Ciprofloxacin
associated with C.diff
Why might you give a sulphonamide and diaminopyramidine together?
synergistic activity
reduce resistance
and more powerful effect!
Whats different between fungus and bacteria?
fungus = eukaryotic
Mechanism of action of anti-fungal drugs?
interfere with the cell membrane
block ergosterol production
or block the cell wall
Give 3 examples of Bactericidal antibiotics?
Penicillins, gentamicin (aminoglycoside), ciprofloxacin
Give 2 examples of Bacteriostatic antibiotics?
Tetracyclines, sulphonamides
In what situation, are bactericidal antibiotics preferred?
in immunocompromised patients, or when infection is in difficult to reach sites (endocarditis, meningitis)
What are the four criteria for switching from IV to oral antibiotics?
COMS
C: Clinical improvement observed
O: Oral route is not compromised
M: Markers showing a trend towards normalising
S: Specific indication of deep infection (ABSENCE OF!)
