Action Mechanisms of Antimicrobials Flashcards
What are three ways an antimicrobial can act?
Inhibition of cell wall synthesis
Inhibition of protein synthesis
Inhibition of nucleic acid synthesis
What are two classes of antimicrobials that inhibit cell wall synthesis?
Penicillins and cephalosporins (beta-lactams)
Glycopeptides
How do penicillins and cephalosporins work?
Disrupt peptidoglycan synthesis by inhibiting the enzymes (PBS) that cross-link the carbohydrate chains
Allows organism destruction by autolytic enzymes
What is resistant to benzyl-penicillin and why?
Gram negative bacteria as the cell wall is made impermeable by the lipopolysaccharide
Give two examples of glycopeptides
Vancomycin and teicoplanin
How do glycopeptides work?
Inhibit the assembly of a peptidoglycan precursor, therefore work prior to beta-lactams
Glycopeptides are suitable for use on what type of bacteria?
Gram positive, as they cannot penetrate the cell wall of Gram negative bacteria
How are glycopeptides administered?
They are not absorbed from the GI tract, only given parenterally
Describe a contraindication and precaution of vancomycin administration?
Toxicity;
IV should be over a few hours
Pre-dose levels should be monitored
Describe the advantages of using teicoplanin over vancomycin
Less toxic
Single daily dose
Same spectrum
What are four classes of antimicrobial that inhibit protein synthesis?
Aminoglycosides
Macrolides and tetracyclines
Oxazolidinones
Cyclic lipopetide
Name an example of an aminoglycoside
Gentamycin
What type of bacteria are sensitive to aminoglycosides?
Staphylococci and Gram negative bacteria
Streptococci are resistant
Describe the administration of aminoglycosides
Can be injected
Describe a contraindication and precaution of aminoglycoside administration
Renal and hearing toxicity
Careful dosing regime required
How are macrolides used and why?
As an alternative to penicillin for use against Gram positive bacteria
(penicillin allergy requires an alternative)
What types of bacteria are resistant to macrolides/tetracyclines?
Many staphylococcus aureus and streptococci species
Describe the improved action of newer macrolides?
Better tissue penetration, therefore lower MIC and better cover for flu strains
What is the only oxazolidinone in common use?
Linezolid
How is linezolid used?
Usually held in reserve for serious infection
Given orally against MRSA
Name an example of a cyclic lipopetide
Daptomycin
How is daptomycin used?
Usually held in reserve for serious infection
Used against MRSA and Gram positive bacteria
What are two classes of antimicrobials that inhibit nucleic acid synthesis?
Trimethoprim and sulphamethoxazole
Fluoroquinolones
How do trimethoprim and sulphamethoxazole work?
Inhibit different steps in purine synthesis
What is the combined form of trimethoprim and sulphamethoxazole and how is it used?
Co-trimoxazole
Used in treatment of chest infections
Why is co-trimoxazole better for use in chest infection treatment than, for example, cephalosporins?
Less likely to cause clostridium difficile infections as a result of their use
Name an example of a fluoroquinolone
Ciprofloxacin
How does ciprofloxacin work?
Inhibits DNA synthesis more directly
How are fluoroquinolones administered?
Orally and parenterally
How are fluoroquinolones used?
Against Gram negative bacteria, including pseudomonas
Describe a contraindication of ciprofloxacin use
Can’t be used in children as it interferes with cartilage growth
Name a newer fluoroquinolone and describe its improved action
Levofloxacin
Has more activity against Gram positive bacteria
Sometimes used in chest infection treatment
How is trimethoprim used on its own?
UTI treatment
