Antimicrobials

Question 1

State the ideal features of an antimicrobial agent?

Answer 1

• 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

Question 2

How do B-lactams act as an antibacterial agent?

Answer 2

• Bind to penecillin binding protein and prevent cross-linking of peptidoglycan cell wall
• Bacterium looses structural integrity and dies

Question 3

How do glycopeptides act as an antibacterial agent?

Answer 3

• Competitively block cell wall linking enzymes and prevent cross linking of peptidoglycan cell wall
• Bacterium looses structural integrity

Question 4

Name a beta-lactam

Answer 4

-Penicillin

Question 5

Name a glycopeptide

Answer 5

-Vancomycin

Question 6

How do quinolones exert their action?

Answer 6

• 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

Question 7

What are the 4 classes of antimicrobial agents?

Answer 7

• Antibacterial
• Antiviral
• Anti fungal
• Antiprotozoal

Question 8

Name a quinolone

Answer 8

• Fluoroquinolone
• Trimethaprim
• Rifampicin

Question 9

What are the 3 main mechanisms of resistance?

Answer 9

• 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

Question 10

What are the two genetic basis of antibiotic resistance?

Answer 10

• Horizontal gene transfer

- Chromosomal gene mutation

Question 11

What are the three mechanisms of horizontal gene transfer?

Answer 11

• Conjugation
• Transduction by phages
• Transformation (introduction, uptake and expression of free foreign DNA)

Question 12

How can antibiotic sensitivity be measured in a laboratory?

Answer 12

• Antibiotic disc sensitivity

- Minimum inhibitory concentration

Question 13

What are the four groups of B-lactams?

Answer 13

• Penicillins
• Cephalosporins
• Carbapenems
• Monobactams

Question 14

Why is flucloxacillin used in staph infections?

Answer 14

-Staph often have b-lactamases which flucloxacillin can resist

Question 15

What is the most common cephalosporin?

Answer 15

-Ceftriaxone

Question 16

What is penicillin mainly active against?

Answer 16

-Streptococci

Question 17

Why is amoxicillin more broad spectrum than penicillin?

Answer 17

-Also active against some gram negative bacteria as well as gram pos

Question 18

Why is there reason for concern with ceftriaxone?

Answer 18

-Associated with C.difficile infections

Question 19

Can you give carbapenem to a penicillin-allergic patient?

Answer 19

• Get history of reaction of penicillin allergy

- Generally safe to give unless anaphylactic

Question 20

What is the target bacteria for vancomycin?

Answer 20

-Active against most gram positive eg staph and strep (not gram neg)

Question 21

How must vancomycin be administered?

Answer 21

• It is not absorbed so given in IV (oral for C.diff)

Question 22

Why must you be careful when using vancomycin?

Answer 22

-It has a very narrow therapeutic window

Question 23

Which antimicrobials act by inhibiting protein synthesis?

Answer 23

• Tetracyclines eg doxycycline
• aminoglycosides eg gentamycin
• macrolides eg erythromycin

Question 24

What is the target bacteria for tetracyclines?

Answer 24

• Broad spectrum ie both gram pos and gram neg

- Also used in atypical pneumonia, chlamydia and some protozoa

Question 25

What is the mode of administration of tetracyclines?

Answer 25

-Oral only

Question 26

What are the target bacteria for aminoglycosides?

Answer 26

-Gram neg

Question 27

Where is gentamycin good at fighting infections?

Answer 27

• Blood/urine

- Generally reserved for severe gram neg sepsis

Question 28

What is a concern when using gentamycin?

Answer 28

-Nephrotoxic/ototoxic so therapeutic drug monitoring required

Question 29

What are the target bacteria for macrolides?

Answer 29

• Mild gram pos infections as an alternative to penicillin

- Atypical respiratory pathogens

Question 30

What is ciprofloxacin and what enzyme does it inhibit?

Answer 30

• Quinolone

- DNA gyrase to prevent nucleic acid synthesis

Question 31

What are the target bacteria for quinolones?

Answer 31

• Gram negs

- Atypical

Question 32

Which antibacterials are used against gram positive bacteria?

Answer 32

• B-lactams (penicillins, cephalosporins and carbapenems)

- Tetracyclines, glycopeptides and Macrolides

Question 33

Which antibacterials are used for gram neg infections?

Answer 33

• Amoxicillin and co-amoxiclav, cephalosporin and carbapenems
• Aminoglycosides
• Quinolones

Question 34

What drug is used to treat UTI?

Answer 34

-Trimethoprim

Question 35

What is the mechanism of action of trimethoprim and sulphonamides?

Answer 35

-Inhibits folic acid synthesis

Question 36

What are the two classes of antifungals?

Answer 36

• Azoles

- Polyenes

Question 37

What is used to treat candida?

Answer 37

-Fluconazole

Question 38

How do antifungals work?

Answer 38

-Inhibit cell wall synthesis and function

Question 39

Amphotericin is used to treat what systemic fungal infection?

Answer 39

-Aspergillus

Question 40

What is Aciclovir?

Answer 40

-Antiviral which inhibits DNA polymerase used to treat herpes simplex and varicella zoster

Question 41

What is metronidazole? What is it used for?

Answer 41

• Antibacterial and antiprotozoal agent

- Anaerobic bacteria and protozoa such as amoebae/giardia

Question 42

How do polymixins work?

Answer 42

-Inhibit cell membrane function

Question 43

What is a side effect of tetracycline?

Answer 43

-Stains teeth