antibiotics Flashcards
mechanism of how antibiotics work.
binds to areas of the bacteria, preventing it from working or killing it
binds to:
- cell wall
- bacteria dna
- ribosome
outline the mechanism how Beta lactam antibiotics work.
- disrupt peptidoglycan production
- by binding covalently and irreversibly to the Penicillin Binding Proteins
- cell wall is disrupted and lysis occurs
- results in a hypo-osmotic or iso-osmotic environment
- Active only against rapidly multiplying organisms
To bind to the PBPs, the β-lactam antibiotic must first diffuse through the bacterial cell wall.
Gram-negative organisms have an additional lipopolysaccharide layer that decreases antibiotic penetration.
Gram-positive usually more susceptible to β-lactams than gram-negative bacteria
Differences in the spectrum and activity of β-lactam antibiotics are due to their relative affinity for different PBPs.
Because the penicillins poorly penetrate mammalian cells, they are ineffective in the treatment of intracellular pathogens.
outline the types of B lactams and the drug names.
Beta Lactams
Penicillins
Penicillin V
Penicillin G (Benzyl penicillin)
Flucloxacillin /Methicillin
Amoxicillin / Ampicillin
Piperacillin
Cephalosporins
Cefalexin
Cefuroxime
Cefotaxime
Ceftriaxone
Ceftazidime
Carbapenems
Meropenem
Ertapenem
Imipenem
Monobactams
Aztreonam
bactericidal vs bacteriostatic antibiotics.
Bactericidal Antibiotics
The agent kills the bacteria
Antibiotics that inhibit cell wall synthesis
Useful if
poor penetration (Endocarditis),
difficult to treat infections or
need to eradicate infection quickly (meningitis)
Kill >99.9% in 18-24 hrs
Bacteriostatic antibiotics:
prevent growth of bacteria
‘inhibitory to growth’
Antibiotics that Inhibit protein synthesis, DNA replication or metabolism
Reduce toxin production and Endotoxin surge less likely*
In fact kill >90% in 18-24 hrs
define minimum inhibitory concentration.
minimum amount of antibiotic required to cure infection so there isnt excess in body
what are the 2 major determinants of anti bacterial effects?
- concentration - needs to inhibit lots of receptors
- time - must inhibit receptors for sufficient period of time
antibiotics work by affecting bacteria nucleic acid.
Ciprofloxacin@
Levofloxacin
Moxifloxacin
Rifampicin
Metronidazole@
Fluoroquinolones
antibiotics work by affecting bacteria ribosomes.
Aminoglycosides
Gentamicin @
Tetracyclines
Doxycycline@
(Tigecycline)
Lincosamides
Clindamycin@
Macrolides
Erythromycin
Clarithromycin@
Azithromycin
Chloramphenicol
antibiotics work by affecting bacteria folate synthesis in the nucleus.
Sulphonamides
Sulphamethoxazole
Trimethoprim@
Co-trimoxazole@
what factors affect how antibiotics work so therefore what do we need to consider when administering it?
A function of
Its release from the dosage form;
Its absorption from the site of administration into the bloodstream; - whats the appropriate route of administeration, IV, oral ect
Its distribution to various parts of the body, including the site of action - Which antibiotics will penetrate that site?What is the pH of the site? Is the antibiotic lipid soluble?
Its rate of elimination from the body via metabolism (LIVER) or excretion (KIDNEY) of unchanged drug. - what dosage interval / duration
what are the ways in which bacteria can be antibiotic resistant?
- change antibiotic target
- destroy antibiotic
- prevent antibiotic access
- remove antibiotic bacteria
outline the bacterial mechanism of changing the antibiotic target for antibiotic resistance.
- Bacteria change the molecular configuration of antibiotic binding site or masks it e.g.
- Bacteria changes the molecular configuration of antibiotic binding site or masks it e.g.
Flucloxacillin (or methicillin) is no longer able to bind PBP of Staphylococci – methicillin resistant S. aureus MRSA
Wall components change in enterococci and reduce vancomycin binding – Vancomicin resistant Enterococci VRE
Rifampicin activity reduced by changes to RNA polymerase in MTB – Rifampicin Resistant TB
outline the bacterial mechanism of destroying the antibiotic for antibiotic resistance.
The antibiotic is destroyed or inactivated e.g.
Beta lactam ring of Penicillins and cephalosproins hydrolysed by bacterial enzyme ‘Beta lactamase’ now unable to bind PBP
The antibiotic is destroyed or inactivated e.g.
Beta lactam ring of Penicillins and cephalosproins hydrolysed by bacterial enzyme ‘Beta lactamase’ now unable to bind PBP
Staphylococci produce ‘penicillinase’ so penicillin but not flucloxacillin inactivated
Gram negative bacteria phosphorylate and acetylate aminoglycosides (gentamicin)
outline the bacterial mechanism of preventing antibiotic access for antibiotic resistance.
modify the bacterial membrane porin channel size, numbers and selectivity e.g.
Pseudomonas aeruginosa against imipenem,
Gram negative bacteria against aminoglycosides
outline the bacterial mechanism of remove antibiotic bacteria for antibiotic resistance.
Proteins in bacterial membranes act as an export or efflux pumps - so level of antibiotic is reduced
S. aureus or S. pneumoniae resistance to fluoroquinolones
Enterobacteriacae resistance to tetracylines
