Session 4 Flashcards
(51 cards)
What are the classifications of antimicrobials?
- Antibacterial
- Antifungal
- Antiviral
- Antiprotozoal
What are bactericidal agents?
Drugs that kill bacteria.
What are bacteriostatic agents?
Drugs that stop the replication of bacteria.
What are broad and narrow spectrum antibiotics?
- Broad-spectrum: kill many bacteria
- Narrow-spectrum: only kill a few types bacteria, very specific
What is classification by target site?
Mechanism of action (eg. how they kill, such as by disintegrating the cell wall)
How to choose an antibiotic?
- Is it active against the organism?
- Can it reach the site of infection? (eg. cross blood-brain barrier)
- Is it available in the right formulation (eg. IV/oral)
- What is the half-life of the drug? (dosing frequency)
- Does it interact with other drugs?
- Are there toxicity issues? (narrow therapeutic windows)
- Does it require therapeutic drug monitoring? (checking if dosage is right)
How to measure antibiotic activity?*
Disc sensitivity testing - measuring the zone of clearance. Biggest zone of clearance means better antibiotic.
Lower concentration of bacteria will be closer to the paper.
What is minimum inhibitory concentration (MIC)?*
- The first concentration of the drug that will inhibit the replication of bacteria.
- Measured by broth microdilution
(broth containing antibiotics is doubling in concentrations)
What is the E-test for MIC? What are its advantages?*
A strip containing antibiotics at different concentrations at various points in a gradient (higher concentrations at the top, lower concentrations at the bottom).
- More clearing at the top, least at bottom
- Quicker than broth microdilution
What are the classes of antibacterials and what are their mechanisms of actions?
Based on the fact that they target different components.
- Cell wall synthesis: beta-lactams and glycopeptides
- Protein synthesis: tetracyclines
- Cell membrane function: polymixins
- Nucleic acid synthesis: quinolones, rifampicin
What is the mechanism of action of penicillin and vancomycin?*
- Prevents bacteria binding the cell wall
- Penicillin binding protein that inhibits the final step of cell wall synthesis
- Penicillin prevents the binding protein from forming cross-linkages as it is now occupied
- Vancomycin stops cell wall from forming by inhibiting the cell wall cross-linking enzyme
What is intrinsic resistance?
- No target or access of the drug
- The drug was never effective as it cannot get to the pathogen
- Permanent
What is acquired resistance?
- Mutates or acquires new genetic material (eg. plasmids)
- Forms resistance against the antibiotics and it’s no longer effective
- Usually permanent
What is adaptive resistance?
- The organism responds to a stress (eg. barely effective level of antibiotic)
- Will go back to being sensitive after use is stopped for a while
What are the mechanisms of resistance to drugs?
- Enzymatic modification of the antibiotic
- Enzymatic alteration of target (eg. binding protein mutating so penicillin can’t bind)
- Mutation of bacterial target site
How do chromosomal gene mutations happen?*
- Small % of bacteria resistant to antibiotic - rest will be killed off, the resistant ones live
- Resistant bacteria replicates and passes on the resistance gene
What is horizontal gene transfer?*
- Gene transfer via a plasmid (mobile genetic element)
- Can be different bacterial SPECIES
- All daughter bacteria will also contain the plasmid
- Allows spread and outbreak
Wha are beta-lactam antibiotics?
- Most commonly used
- Range from broad to narrow spectrum
- Largest group of antibiotics
- Characterised by a beta-lactam ring
What are monobactams?
- Most narrow-spectrum beta-lactams
- Only used for very resistant bacteria
What are types of penicillins and what are they mainly active against?
- Penicillin: streptococci
- Amoxicillin: Gram-negatives
- Flucloxacillin: stapylococci + steptococci
What are beta-lactamase inhibitor combinations?
Combinations of drugs that contain enzymes which will break down the beta-lactam ring for more stability.
What are some examples of beta-lactamase inhibitor combinations and what are they effective against?
- Co-amoxiclav - all above, anaerobes, gram negatives
- Piperacillin/tazobactam - all above + gram negatives, including pseudomonas (VERY BROAD SPECTRUM)
What are cephalosporins?
Antibiotics that are usually very good at treating gram negative bacteria but not as good at treating gram positive bacteria
- Broad spectrum
- No anaerobe activity
What infections can’t be treated with cephalosporins and why?
Abdominal/bowel infections are usually anaerobic and cephalosporins have no anaerobe activity.
