Antibacterial agents

Question 1

Definition of antibiotic

Answer 1

Chemical product of microbe that inhibits or kills another organism

Question 2

Types of antimicrobial agent (3)

Answer 2

Antibacterial
Anti fungal
Antiviral

Question 3

Definition of bacteriostatic

Answer 3

Inhibition of bacterial growth

Question 4

Definition of bactericidal

Answer 4

Kill bacteria

Question 5

What is the MiC?

Answer 5

Minimum Inhibitory Concentration - minimum concentration of antibiotic at which visible growth is inhibited

Question 6

What is synergism?

Answer 6

The activity of two antimicrobials given together, giving a greater sum of activity than if given separately

Question 7

What is antagonism?

Answer 7

When one agent diminishes the activity of another

Question 8

What is indifference?

Answer 8

When activity is unaffected by the addition of another agent

Question 9

Give examples of antibiotic targets

Answer 9

Cell wall
Protein synthesis
DNA synthesis
RNA synthesis
Plasma membrane

Question 10

What is the major component of the bacterial cell wall?

Answer 10

Peptidoglycan Present in gram positive and gram negative bacterium - polymer of glucose derivatives, N-acetly muramic acid (NAM) and N-acetyl glucosamine (NAG)

Question 11

Given examples of cell wall synthesis inhibitors

Answer 11

Beta-lactams
Glycopeptides
Cycloserine (anti-tuberculous agent)
Fosftomycin (antibacterial not available in UK)

Question 12

How do beta-lactams work?

Answer 12

Contain beta-lactam ring, which is a structural analogue of D-alanyl-D-alanina, so interferes with function of “penicillin-binding proteins”

Question 13

Give examples of beta-lactam antibiotics

Answer 13

Penicillins
Cephalosporins
Carbapenems
Monobactams

Question 14

Which bacteria do glycopeptides act upon?

Answer 14

Gram positive - unable to penetrate gram-negative outer membrane
Examples: vancomycin, teicoplanin

Question 15

Give examples of classes of protein synthesis inhibitors

Answer 15

Aminoglycosides e.g. gentamicin, bind to 30S ribosomal subunit
Macrolides e.g. erythromycin
Lincosamides e.g. clindamycin, bind to 50S ribosomal subunit
Streptogramins
Tetracyclines e.g. doxytetracycline, bind to 30S ribosomal subunit
Oxazolidinones e.g. linezolid, binds to 50S ribosomal subunit

Question 16

Give examples of DNA synthesis inhibitors

Answer 16

Trimethoprim - inhibits dihydrofolate reductase
Sulphonamides - inhibit dihydropteroate synthesise (enzyme that allows first step of folic acid production)
Quinolone e.g. nalidixic acid
Fluoroquinones e.g. ciproflaxin

Question 17

Give examples of RNA synthesis inhibitors

Answer 17

Rifampicin - RNA polymerase inhibitor

Question 18

Give examples of plasma membrane agents

Answer 18

Colistin - gram negatives

Daptomycin - gram positives

Question 19

What are the adverse effects of ahminoglycosides?

Answer 19

Reversible renal impairment on accumulation, irreversible ototoxicity - therapeutic drug monitoring indicated

Question 20

What are the adverse effects of beta-lactams?

Answer 20

Allergic reactions:
Generalised rash 1-10%
Anaphylaxis approx. 0.01%
Minor allergic skin reactions
Severe allergic skin reactions - Stevens-Johnson syndrome
Angio-oedema, bronchospasm, urticaria, anaphylaxis

Question 21

What are the adverse effects of linezolid?

Answer 21

Bone marrow depression

Question 22

In patients with non-severe penicillin allergy, which antibiotics are safe to use?

Answer 22

Carbapenems
Cephalosporins
*Aztreonam is safe to use in all penicillin allergies - doesn’t contain bicyclic nucleus

Question 23

Which 4 common antibiotics precipitate C.difficile?

Answer 23

Co-amoxiclav (amoxicillin-clavulante)
Cephalosporins
Cirpofloxacin
Clindamycin

Question 24

What are the three main reasons for combining antibiotics?

Answer 24

To increase efficacy
To provide adequately broad spectrum
To reduce resistance