M: Antibiotic Action 2 - Week 9 Flashcards
Describe the mechanism of action of aminoglycosides (2). What does this give rise to? (3)
Aminoglycosides bind to the cytosolic, membrane-associated bacterial ribosome. Aminoglycoside presence in cytosol disturbs peptide elongation at the 30S ribosomal subunit, giving rise to:
- inaccurate mRNA translation
- misreading of the mRNA code
- biosynthesis of truncated or proteins with altered amino acid composition
In regards to Aminoglycosides, describe the following:
A: Bactericidal or Bacteriostatic?
B: What is the spectrum of microorganisms they work on
C: Level of toxicity
D: When to use
A: bactericidal
B: gram -ve aerobic bacteria (also gram +ve bacteria)
C: significant toxicity
D: reserve for serious infections
Why don’t we generally use aminoglycosides to treat gram +ve bacteria?
Because other, less toxic antibiotics are more suitable
Name 4 aminoglycosides
- gentamicin
- tobramycin
- amikacin
- neomycin
In regards to Tetracyclines, describe the following:
A: How do they work/mechanism?
B: Bactericidal or Bacteriostatic?
C: Level of toxicity
D: How often is it used? What does this suggest?
A: bind 30S subunit and prevent alignment of tRNAs
B: Generally bacteriostatic
C: Low toxicity
D: Widely used, suggesting that resistance may be a problem
Name one condition that tetracyclines are useful for. Is there anything important to note here?
useful for Chlamydia. Note: that we may need to treat at other sites, so topical treatment may be added to the oral treatment
Name 3 side-effects that can occur with tetracyclines
- nausea
- phototoxicity
- discoloration of teeth in children under 6 yrs old
In regards to Chloramphenicol, describe the following:
A: How does it work/mechanism?
B: Bactericidal or Bacteriostatic?
C: Level of toxicity
D: Broadness of spectrum of microorganisms it affects
E: Form of administration
A: inhibits peptidyl transferase, blocks chain elongation
B: Bacteriostatic
C: significant toxicity
D: Broad spectrum, highly effective
E: topical preparations available
Name one potential side effect of Chloramphenicol
irreversible aplastic anaemia
In regards to Macrolides, describe the following:
A: Name 2 of them
B: Mechanism of action
C: Broadness of spectrum
A: Ezithromycin, Azithromycin
B: Bind 50S subunit, prevent translocation of peptides
C: Broad spectrum
Name 2 antimicrobial agents that are particularly useful in treating chlamydia
- tetracyclines
- macrolides
For antimicrobial agents that target the nucleic acid of microorganisms: name the 3 ways they can act, and provide an example for each
1: Inhibition of synthesis of precursors - sulphonamides, trimethoprim
2: Inhibition of DNA replication - quinolones
3: Inhibition of RNA polymerase - rifampicin
How can antimicrobial agents inhibit the synthesis of nucleic acid precursors? i.e. What pathway do they act on?
by acting on microbial folate synthesis
How do the following agents act to inhibit nucleic acid precursors:
A: Sulphonamides
B: Tremethroprim
A: Sulphonamides - inhibit folate synthesis by enzyme inhibition
B: inhibits folate required for the synthesis of purines and pyrimidines by enzyme inhibition
In regards to Quinolones:
A: What part of DNA replication process do they affect?
B: What is this part responsible for?
C: Are quinolones bactericidal or bacteriostatic?
D: Describe their spectrum of activity
A: DNA gyrase
B: is required to supercoil the bacterial DNA
C: bactericidal
D: Good activity against pseudomonas, but resistance is rapid and increasing in isolates from other sites
Name 2 examples of fluoroquinolones
- ciprofloxacin
- ofloxacin
Describe the spectrum activity and resistance levels of fluoroquinolones. How do we maintain maximal efficacy of fluoroquinolones?
Broad spectrum activity with relatively little microbial resistance.
- to maintain maximal efficacy of these preparations, fluoroquinolones should not be used when alternative, equally effective agents could be used instead
List 6 questions you should be asking when considering the use of an antimicrobial agent
- is it an infection?
- is an antibiotic actually needed?
- what is the likely pathogen, and which are the major antibiotics active against this pathogen?
- with regard to these antibiotics, which are the safest and narrowest spectrum?
- how should the antibiotic be provided (dose, interval, duration?)
- if one antibiotic is good, are more better?
Provide 3 valid reasons to use antibiotic combinations
- To cover the range of organisms which might reasonably be expected to be present
- To achieve synergy (e.g. a penicillin + an aminoglycoside for resistant pseudonomas infection)
- To cover the possibility of the presence of antibiotic resistant mutants in the population (e.g. in mycobacterial infections)
What does the therapeutic guidelines recommend for treatment of blepharitis caused by staph? (4)
Lid hygeine: remove debris, warm compress, gentle scrub of lashes, antibiotic efficacy uncertain (chloramphenicol 1% ointment 1-2x daily, 1wk)
What does the therapeutic guidelines recommend for treatment of chronic blepharitis assoc. with rosacea? (2)
Lid hygeine, doxycyline orally (daily for 8 wks)
What does the therapeutic guidelines recommend for EMPIRICAL treatment of conjunctivitis? (2)
“Delayed prescription” approach: chloramphenicol or framycetin drops for empirical treatment
What does the therapeutic guidelines recommend for treatment of conjunctivitis? (when indicated/non-empirical) (3)
gentamycin, tobramycin, and quinolone drops when indicated
What does the therapeutic guidelines say for the treatment of conjunctivitis associated with chlamydia? (1)
successful treatment requires systemic therapy with azithromycin (orally)
What does the therapeutic guidelines recommend for treatment of HSV keratitis?
Acyclovir 3% ointment (5x daily, 14 days)
Describe 3 methods of antibacterial treatment for bacterial keratitis. Under what situations do you use either of these treatments?
- ciprofloxacin 0.3% eye drops: 1 drop into affected eye, every hour (incl. overnight)
- oflaxacin 0.3% eye drops: 1 drop into affected eye, every hour (incl. overnight)
- cefazolin 5% + gentamycin 0.9% eye drops: 1 drop into affected eye, every hour (incl. overnight)
- these topical treatments should be used in the case that referral is delayed