Antimicrobials Flashcards
State the ideal features of an antimicrobial agent?
- Selectively Toxic (onlt targets that bacteria)
- Long Half Life (infrequent dosing improves compliance)
- No interference with other drugs
- Few adverse effects
- Reach site of infection (ef penetration of CSF)
- Oral/IV formulation
How do B-lactams act as an antibacterial agent?
- Bind to penecillin binding protein and prevent cross-linking of peptidoglycan cell wall
- Bacterium looses structural integrity and dies
How do glycopeptides act as an antibacterial agent?
- Competitively block cell wall linking enzymes and prevent cross linking of peptidoglycan cell wall
- Bacterium looses structural integrity
Name a beta-lactam
-Penicillin
Name a glycopeptide
-Vancomycin
How do quinolones exert their action?
- Inhibition of nucleic acid synthesis and repair
- Bind to enzymes involved in DNA replication (such as topoisomerase) and inhibit it.
- Without DNA replication the cell will die
What are the 4 classes of antimicrobial agents?
- Antibacterial
- Antiviral
- Anti fungal
- Antiprotozoal
Name a quinolone
- Fluoroquinolone
- Trimethaprim
- Rifampicin
What are the 3 main mechanisms of resistance?
- Drug inactivating enzymes eg b-lactamases
- Altered Target site eg target enzyme has lower affinity for drug
- Altered uptake eg decreased permeability or increased efflux
What are the two genetic basis of antibiotic resistance?
- Horizontal gene transfer
- Chromosomal gene mutation
What are the three mechanisms of horizontal gene transfer?
- Conjugation
- Transduction by phages
- Transformation (introduction, uptake and expression of free foreign DNA)
How can antibiotic sensitivity be measured in a laboratory?
- Antibiotic disc sensitivity
- Minimum inhibitory concentration
What are the four groups of B-lactams?
- Penicillins
- Cephalosporins
- Carbapenems
- Monobactams
Why is flucloxacillin used in staph infections?
-Staph often have b-lactamases which flucloxacillin can resist
What is the most common cephalosporin?
-Ceftriaxone
What is penicillin mainly active against?
-Streptococci
Why is amoxicillin more broad spectrum than penicillin?
-Also active against some gram negative bacteria as well as gram pos
Why is there reason for concern with ceftriaxone?
-Associated with C.difficile infections
Can you give carbapenem to a penicillin-allergic patient?
- Get history of reaction of penicillin allergy
- Generally safe to give unless anaphylactic
What is the target bacteria for vancomycin?
-Active against most gram positive eg staph and strep (not gram neg)
How must vancomycin be administered?
- It is not absorbed so given in IV (oral for C.diff)
Why must you be careful when using vancomycin?
-It has a very narrow therapeutic window
Which antimicrobials act by inhibiting protein synthesis?
- Tetracyclines eg doxycycline
- aminoglycosides eg gentamycin
- macrolides eg erythromycin
What is the target bacteria for tetracyclines?
- Broad spectrum ie both gram pos and gram neg
- Also used in atypical pneumonia, chlamydia and some protozoa
What is the mode of administration of tetracyclines?
-Oral only
What are the target bacteria for aminoglycosides?
-Gram neg
Where is gentamycin good at fighting infections?
- Blood/urine
- Generally reserved for severe gram neg sepsis
What is a concern when using gentamycin?
-Nephrotoxic/ototoxic so therapeutic drug monitoring required
What are the target bacteria for macrolides?
- Mild gram pos infections as an alternative to penicillin
- Atypical respiratory pathogens
What is ciprofloxacin and what enzyme does it inhibit?
- Quinolone
- DNA gyrase to prevent nucleic acid synthesis
What are the target bacteria for quinolones?
- Gram negs
- Atypical
Which antibacterials are used against gram positive bacteria?
- B-lactams (penicillins, cephalosporins and carbapenems)
- Tetracyclines, glycopeptides and Macrolides
Which antibacterials are used for gram neg infections?
- Amoxicillin and co-amoxiclav, cephalosporin and carbapenems
- Aminoglycosides
- Quinolones
What drug is used to treat UTI?
-Trimethoprim
What is the mechanism of action of trimethoprim and sulphonamides?
-Inhibits folic acid synthesis
What are the two classes of antifungals?
- Azoles
- Polyenes
What is used to treat candida?
-Fluconazole
How do antifungals work?
-Inhibit cell wall synthesis and function
Amphotericin is used to treat what systemic fungal infection?
-Aspergillus
What is Aciclovir?
-Antiviral which inhibits DNA polymerase used to treat herpes simplex and varicella zoster
What is metronidazole? What is it used for?
- Antibacterial and antiprotozoal agent
- Anaerobic bacteria and protozoa such as amoebae/giardia
How do polymixins work?
-Inhibit cell membrane function
What is a side effect of tetracycline?
-Stains teeth
