Antimicrobial agents

Question 1

Which antibiotics cannot be used in penicillin allergic patients due to cross-sensitivity?

Answer 1

Penicillins, cephalosporins and carbapenams have cross-reactivity in up to 10% of penicillin allergic patients.

Question 2

Which of the following could be used in a severely penicillin allergic patient?

(piperacillin, teicoplanin, cefradine, clarithromycin, imipenem)

Answer 2

Piperacillin - NO penicillin

Cefradine - NO cephalosporin

Imepenem - NO carbapenem

Teicoplanin - YES glycopeptide

Clarithromycin - YES macrolide

Question 3

Which of the following have anaerobic cover?

(imipenem, metronidazole, trimethoprim, aztreonam, vancomycin)

Answer 3

Imipenem - wide spectrum including some anaerobes

Metronidazole - only covers anaerobes and parasites

Question 4

What is aztreonam?

Answer 4

Aztreonam is a monobactam with no useful activity against anaerobes or gram-positive organisms; it covers a wide range of gram-negative bacteria.

Question 5

What are the bacteriocidal antibiotics?

Answer 5

Penicillins, cephalosporins, carbapenems, aminoglycosides, quinolones, metronidazole, vancomycin.

Question 6

What are the bacteriostatic antibiotics?

Answer 6

Sulphonamides, tetracyclines.

Question 7

Which of the following antibiotics are bactericidal?

(piperacillin, cefotaxime, imipenem, clindamycin, rifampicin)

Answer 7

All except clindamycin (bacteriostatic lincosamide antibiotic)

Question 8

Are macrolides bacteriocidal or bacteriostatic?

Answer 8

Can be either depending on their plasma concentration

Question 9

What is the MOA of benzylpenicillin?

Answer 9

Inhibits cell wall synthesis

Question 10

How does ceftriaxone work?

Answer 10

Cephalosporins, including Ceftriaxone, inhibit cell wall synthesis as do all beta-lactam antibiotics.

Their beta-lactam ring binds to proteins and prevents peptidoglycan cross-linkage in the bacterial cell-wall thus weakening it.

Question 11

What does gentamicin do?

Answer 11

Gentamicin arrests bacterial protein synthesis by binding to the 30S ribosomal RNA subunit

Question 12

What does ciprofloxacin do?

Answer 12

INhibits DNA gyrase

Question 13

What does rifampicin do?

Answer 13

Rifampicin binds to the beta-subunit of DNA-dependent RNA polymerase, preventing bacterial protein synthesis.

Question 14

What antibiotics cover MRSA?

Answer 14

Meropenem, Ciprofloxacin, Vancomycin, Clindamycin, Fusidic acid and Teicopleinin.

Question 15

What antibiotics treat C. Diff?

Answer 15

Metronidazole and vancomycin

Question 16

Which antibiotics provide good gram-negative cover?

Answer 16

Aztreonam

Gentamicin

Ciprofloxacin

Question 17

How does amphotericin B work?

Answer 17

Creates pores in fungal cell membrane

Question 18

Is miconazole absorbed orally?

Answer 18

No, all azoles EXCEPT miconazole are well absorbed orally

Question 19

Which routes can amphotericin B be given?

Answer 19

IV only

Question 20

Does the dose of ketoconazole need to be reduced in renal failure?

Answer 20

Ketoconazole is metabolised in the liver and inactive metabolites are excreted in the bile, hence no dose adjustment is required in renal failure.

Question 21

How do azoles work?

Answer 21

By affecting funcal ergosterol synthesis

Question 22

Can vancomycin cause ototoxicity?

Answer 22

Yes

Question 23

Which antibiotic causes red discolouration of body fluids?

Answer 23

Rifampicin

Question 24

How do aminoglycosides affect NDMRs?

Answer 24

Aminoglycosides increase potency of NDMRs by decreasing pre-junctional release of ACh and reducing the sensitivity of post-junctional receptors to ACh.

Question 25

What effect can tetracycline have on children?

Answer 25

Discolouration of teeth

Question 26

Which drug is associated with red man syndrome?

Answer 26

Vancomycin (histamine release and widespread rash)

Question 27

Which antibiotics are significantly sensitive to beta-lactamases produced by bacteria?

Answer 27

Beta-lactam antibiotics are sensitive to beta-lactamase enzymes produced by resistant bacteria; different antibiotics in this class have differing degrees of sensitivity. Benzylpenicillin and Piperacillin are sensitive.

However Meropenem is very resistant to beta-lactamases, and Flucloxacillin is moderately beta-lactamase resistant.