L2_Antibiotics: A logical approach Flashcards
On what basis are antibiotics categorised into groups?
- by their mechanism of action.
What is the name given to the group of antibiotics that inhibit cell wall synthesis or function?
Give 3 examples.
- β-lactams.
- penicillins.
- cephalosporins.
- vancomycin.
What is the difference between bactericidal and bacteriostatic antibiotics?
Give an example of an antibiotic for each.
- bactericidal = kills the bacteria. e.g. (all β-lactams) penicillin.
- bacteriostatic = prevent further bacterial replication. e.g. macrolides.
Give a brief explanation of MoA of penicillin.
- inhibits cell wall formation by preventing PDG cross-linkage.
- irreversibly binds to penicillin-binding proteins (transpeptidase) in the cell wall.
- these proteins are involved in the final step of PDG cross-link formation.
Explain the role of β-lactamase in relation to penicillin.
- beta-lactamase hydrolyses the lactam ring in penicillin causing it to lose its structure and therefore rendering it inactive as an antibiotic.
How can bacteria grow resistant against penicillin?
- many bacteria contain the gene code for β-lactamase which can be passed on to the next generation of bacteria through plasmids.
Give one way to overcome the issue of antibiotic resistance with regards to penicillin.
- a combination of amoxicillin and clavulanic acid can be administered.
- clavulanic acid is a β-lactamase inhibitor.
What feature of cephalosporins make them more stable than penicillins?
- they have a modified β-lactam ring which makes them less susceptible to β-lactamases.
How is vancomycin different to penicillin? (2)
- it is a non-β-lactam bactericidal antibiotic.
- it is effective against anaerobic and aerobic gram-POSITIVE bacteria.
In which instance would vancomycin be used?
- colitis (inflammation of the intestine).
- endocarditis.
- skin infections.
- blood stream infections.
- meningitis caused by MRSA.
What features of vancomycin makes it suitable for treating intestinal bacterial infections?
- when taken orally, it is poorly absorbed from the intestines, therefore prolonging its activity within the intestines.
What is teicoplanin and when is it typically used?
- an antibiotic used in prophylaxis of MRSA.
- comes in a powder which can be dissolved in water.
- cell-wall synthesis inhibitor.
What is the therapeutic range in which vancomycin must remain in a patient? Why must the concentration not fall out of this range?
- 10-15 mg^L.
- below = bacteria can continue to replicate.
- above = renal toxicity.
Which antibiotics inhibit bacterial protein synthesis? Give an example of antibiotics inhibiting the large (50s) subunit and the small (30s) subunit.
- large subunit = macrolides (erythromycin).
- small subunit = gentamicin
Why is erythromycin a good antibiotic for lower and upper respiratory tract infections?
- due to its strong sputum and lung penetration.
Which three drugs does erythromycin have interactions with? (3)
- warfarin, statins and carbomazepine.
Briefly describe the MoA of erythromycin.
- it inhibits the 50s subunit of ribosomes in bacteria.
- preventing the ribosome to move along the mRNA chain and therefore preventing the production of proteins.
Briefly describe the MoA of gentamicin.
- bacteriostatic against aerobic gram-NEGATIVE bacteria.
- needs oxygen for active transport (bc it is not hydrophilic) across the membrane of gram-ve bacteria.
- attaches to transfer RNA.
Why can’t gentamicin be given orally?
- bc it is not lipophilic therefore has poor absorption into the systemic circulation.
- needs to given as IV.
How does gentamicin cause ototoxicity?
- due to large rapid IV doses.
- causes a peak in plasma conce which leads to higher uptake in the lymph in the middle ear –> killing the hearing cells.
Which group of antibiotics inhibit DNA synthesis?
- flouroquinolones = ciprofloxacin.
Which group of antibiotics inhibit folate synthesis?
- trimethoprim.
Which group of antibiotics create free radicals?
- metronidazol.
What is the mechanism of action of ciprofloxacin?
- it blocks DNA replication.
- broad-spec antibiotic.
- bacteriostatic.
- it inhibits topoisomerase (enzyme in bacteria required to separate the DNA strands in order to initiate replication).
Pros of ciprofloxacin:
- well absorbed orally.
- limited metabolism from liver so excreted mostly unchanged.
- good distribution into CNS.
Which two drugs constitute septrim?
- trimethoprim and sulfamethoxazole
What is the MoA of septrim?
- inhibits sequential steps in the folic acid synthesis process in bacteria.
What is the MoA of metronidazole?
- effective against anaerobes.
- acts as an electron sink.
- allowing for free radicals to accumulate within the cell creating the illusion that the cell is in an oxygen rich environment.
- enters bacterial cells via passive diffusion.
- the free radicals eventually cause DNA breakage.
Pros of metronidazole:
- nearly 100% bioavailability.
Cons of metronidazole:
- can’t drink alcohol with it.
