Antibiotics

Question 1

How are beta lactams excreted

Answer 1

In the urine

Question 2

How do microbes develop resistance to beta lactams

Answer 2

Altered or different penicillin-binding proteins so antibiotic cant bind
Changes in specific pumps filtering out the drug
Changes in porin size or number (gram negative organisms) prevents drugs from gaining access to intracellular targets.

Inactivation by beta-lactamases – most common
Gram neg bacteria have it in their cell wall
Others get it induced after exposure to the drug

Question 3

List major beta lactams

Answer 3

Cephalosporins, penicillins, carbepenems, and monobactams

Question 4

Beta lactam MOA

Answer 4

Interferes with bacterial cell wall synthesis and causes cell wall degradation

Question 5

Beta lactam time or concentration dependent

Answer 5

Time dependent

Question 6

MRSA resistance MOA

Answer 6

Use of Beta lactamase protectors – clavulanic acid or sulbactam – led to adaptation by Staph by mutations in penicillin-binding proteins (PBP-2) encoded by mecA gene, located on the staphylococcal chromosomal cassette.
Expression of this gene prevents efficacy of any beta-lactam antibiotic

Question 7

T/F: Beta lactams do not work well in hypoxic and hypertonic environments (e.g. abscesses)

Answer 7

True

Question 8

Beta lactam - Efficacy in hypertonic environment

Answer 8

Does not work well in hypertonic environment (e.g. renal interstitium)

Question 9

How to minimize nephrotoxicity associated with aminoglycosides

Answer 9

Add dietary calcium to protect against toxicity
Allow kidneys drug-free period (high once daily dosing)
Alkaline urine increases activity and decreases renal tubular cell uptake (reduces chance of tox)

Question 10

List some aminoglycosides

Answer 10

Neomycin, gentamicin, amikacin, netilmicin, and streptomycin

Question 11

Aminoglycosides MOA

Answer 11

Target bacterial ribosomes – 30s ribosomal subunit

Question 12

Aminoglycosides bactericidal or static
Time or concentration dependent

Answer 12

Bactericidal and concentration-dependent

Question 13

Aminoglycosides in purulent material

Answer 13

Not efficacious due to acidic environment

Question 14

Is presence of renal disease a contraindication for administering aminoglycosides

Answer 14

No

Question 15

Aminoglycosides and oxygen

Answer 15

Uptake depends on membrane bound respiratory protein therefore anaerobes are resistant - Lack of oxygen renders aminoglycosides ineffective

Question 16

How do hyperosmolarity and decreased pH affect aminoglycosides

Answer 16

Hyperosmolarity and decreased pH also decrease drug movement into the cell

Question 17

MOA of fluoroquinolones

Answer 17

Inhibits DNA synthesis via DNA gyrase – only veterinary microbial that does so

Question 18

Benefits of fluoroquinolones

Answer 18

Still good in low oxygen tension
Accumulate in WBC
Broad gram-negative spectrum

Question 19

Are fluoroquinolones bactericidal or static
time or concentration dependent

Answer 19

Bactericidal
Concentration dependent

Question 20

Antibiotic recommended for hepatobiliary surgery

Answer 20

Cefoxitin

Question 21

Which combination would be best for a gram positive aerobic and gram negative anaerobic infection

Answer 21

AGs or FQs are often combined with beta lactams, metro, or clindamycin to target both aerobic G+ and G- infections, or infections caused by both aerobes and anaerobes

Question 22

Which antibiotics cross the blood-brain barrier in the presence of inflammation

Answer 22

Penicillins
Selected cephalosporins (e.g., cefotaxime, ceftriaxone, ceftazidime)
Fluorinated quinolones
Vancomycin

Question 23

Which antibiotics cross the blood-brain barrier

Answer 23

Chloramphenicol
Doxycycline
FQ (for some organisms)
Metronidazole
Rifampin
Sulfonamides/trimethoprim

Question 24

Which antibiotics DO NOT cross the blood-brain barrier

Answer 24

Aminoglycosides
Carbenicillin
Cephalothin
Cefazolin
Cefotetan
Clindamycin
Erythromycin
Tetracycline

Question 25

hyperosmolar environment affects on drugs

Answer 25

Hyperosmolar environment: may occur in inflammatory debris – reduces osmotic destruction of the organisms and causes drugs that target cell walls (beta-lactams in particular) to be less effective.