antibiotics

Question 1

what are the seven categories of antibiotics?

Answer 1

1 - antimetabolites (sulfonamides)
2 - inhibitors of cell wall synthesis (B-lactams, glycopeptides)
3 - agents that alter membrane permeability (polymyxins, polyenes)
4 - inhibitors of protein synthesis (aminoglycosides, macrolides, tetracycline, chloramphenicol)
5 - inhibitors of DNA replication (quinolone)
6 - inhibitors of RNA replication (rifampin)
7 - miscellaneous antibiotics

Question 2

what is an antimetabolite?

Answer 2

interferes with synthesis of function of a substance involved in normal cell metabolism

Question 3

mechanism of sulfonamides?

Answer 3

• broad spectrum

- penetrate sensitive bacteria and inhibit production of folic acid through competitive inhibition

Question 4

why is folic acid important for cell metabolism?

Answer 4

bacterial DNA synthesis -

Question 5

Is the action of sulfonamides reversible?

Answer 5

yes - bacteriostatic

Question 6

name the three antimetabolites we are responsible for.

Answer 6

1 - sulfonamides
2 - trimethoprim
3 - isoniazid

Question 7

trimethoprim action

Answer 7

• synergistic with sulfonamides
• inhibits enzyme that converts dihydrofolate to tetrahydrofolate
• used with sulfonamides (sulfamethoxazole) for UTIs

Question 8

isoniazid action

Answer 8

• narrow spectrum (M. tuberculosis)
• interferes with mycolic acid synthesis (mycobacteria)
• bactericidal
• inhibits enzyme InhA - fatty acid elongation
• penetrates human cell wall to kill intracellular bacteria

Question 9

name seven antibiotics that are inhibitors of cell wall synthesis

Answer 9

1 - penicillin
2- cephalosporins
3 - beta-lactam rings but not penicillin
4 - beta-lactamase inhibitors
5 - glycopeptides
6 - cycloserine
7 - bacitracin

Question 10

why such a large difference in sensitivity between animal cells and bacteria with penicillin?

Answer 10

animal cells don’t have a cell wall.

Question 11

what is a lactam?

Answer 11

an anhydride link that forms a ring structure in part of a molecule - strained and easily hydrolyzed

Question 12

how does penicillin kill cells?

Answer 12

• B-lactam antibiotic
• bind to and inactivate penicillin binding proteins (PBPs) - which are responsible for terminal stages of cell wall reshaping during growth and division

Question 13

how can you prevent or slow the lethal action of penicillin?

Answer 13

deprive bacteria of nutrients essential for growth. bacteria must be able to divide once or twice.

Question 14

how can penicillin be hydrolyzed?

Answer 14

1 - acidity of the stomach

2 - penicillinases in bacteria

Question 15

penicillin G is sensitive to:

Answer 15

acid hydrolysis and penicillinase

Question 16

penicillin V is sensitive to:

Answer 16

penicillinase only

Question 17

ampicillin is sensitive to:

Answer 17

penicillinase only

Question 18

pencillin G is effective against:

Answer 18

• many gram-positive, sensitive cocci
• some gram-negative cocci (meningitis)
• spirochete (treponema pallidum - syphilis)

Question 19

shortcomings of penicillin G

Answer 19

• no oral formulation because acid labile
• penicillinase sensitivity
• ## potential allergic response

Question 20

what are some semi-synthetic penicillins and how are they used?

Answer 20

• oxacillin, nafcillin

- used against bacteria that produce penicillinase

Question 21

penicillins that are sensitive to penicillinase and are limited spectrum include:

Answer 21

• penicillin G - acid labile
• penicillin V - relatively acid stable
• Penicillin VK - higher solubility

Question 22

penicillins sensitive to penicillinase that are broader spectrum

Answer 22

• ampicillin - acid stable

- amoxicillin - acid stable

Question 23

penicillins sensitive to penicillinase that are extended spectrum (more bacilli, less G+ cocci)

Answer 23

• tricarcillin - b-lactam effective against pseudomonas aeruginosa
• piperacillin - most active against G- bacilli

Question 24

penicillins resistant to penicillinase

Answer 24

• methicillin - acid labile

- naficillin, dicloxacillin, oxacillin - newer, more potent, acid resistant (oral available)

Question 25

What does MRSA stand for?

Answer 25

methicillin resistant staphylococcus aureus

Question 26

penicillin structure

Answer 26

- 4 membered b-lactam ring | - thiazolidine ring

Question 27

- CWSI - cephalosporin structure

Answer 27

- 4 membered b-lactam ring | - dihydrothiazine ring

Question 28

- CWSI - cephalosporin characteristics

Answer 28

- also bactericidal (cell wall inhibitor) - broad spectrum against G+ and some G- bacilli - GREATER acid stability than penicillin - resistant to some penicillinases

Question 29

first gen cephalosporins and effectiveness

Answer 29

- cefazolin, cephalexin, cefaclor, cephalothin | - G+ cocci, some G- bacilli, NOT pseudomonas aeruginosa

Question 30

second gen cephalosporins and effectiveness

Answer 30

- cefuroxime, cefamandole, cefonocid, cefotetan, cefoxitin | - less effective against G+, more against G- enterics, still NO P. aeruginosa

Question 31

third gen cephalosporins and effectiveness

Answer 31

- ceftriaxone, ceftazidime, cefotaxime, cefoperazone - broader G- spectrum - ceftazidime - gets P. aeruginosa - ceftriaxone - penetrates CNS

Question 32

CWSI - B-lactam ring antibiotics that are not penicillin include:

Answer 32

- monobactams (aztreonam) - G- and P. aeruginosa | - carbapenems (imipenem) - broadest spectrum and most resistant to most b-lactamases

Question 33

CWSI - 3 B-lactamase inhibitors

Answer 33

1 - clavulanic acid - (augmentin - with amoxicillin) 2 - sulbactam (unasyn - with ampicillin) 3 - tazobactam (zosyn - with piperacillin)

Question 34

CWSI - glycopeptides - 2 important drugs

Answer 34

1 - vancomycin | 2- teicoplanin

Question 35

vancomycin characteristics

Answer 35

- restricted to G+ organisms - binds R-D-Ala-D-Ala which blocks peptidoglycan precursor transfer - somewhat toxic but used when other drugs are contraindicated - ONLY drug available for multiply resistant enterococcus (MRE) and MRSA

Question 36

teicoplanin characteristics

Answer 36

- chemically similar to vancomycin - greater lipophilicity - excellent tissue and intracellular phagocytic penetration - NO oral formulation, very expensive - not approved by FDA yet

Question 37

CWSI - cycloserine

Answer 37

- secondary TB drug | - toxic

Question 38

CWSI - bacitracin

Answer 38

- restricted to G+ - toxic, topical only - found in Neosporin with polymyxin B or neomycin

Question 39

antibiotics that affect membrane permeability contrast to b-lactams

Answer 39

- cell growth not required for activity

Question 40

antibiotics that affect membrane permeability - examples

Answer 40

1 - polymyxins B and E: effective against G- enteric rods | 2 -