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Pharmacology Final > Beta-Lactam Antibiotics > Flashcards

Beta-Lactam Antibiotics Flashcards

1
Q

classes of beta lactams

A

penicillins, cephalosporins, carbapenems, monobactams

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2
Q

what characteristic do all members of beta-lactams share?

A

they all share a similar structure: the beta-lactam ring that is essential for activity
- substitutions on the ring are used to increase resistance to beta-lactamase enzymes, enhance

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3
Q

penicillin drug classifications

A
  • natural penicillins: penicillin G
  • amino penicillins: ampicillin, amoxicillin
  • anti-staph penicillins: oxacillin
  • extended spectrum penicillins: piperacillin
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4
Q

penicillin MOA

A
  • prevention of cell wall formation and lysis of bacteria: bactericidal action!
  • inhibition of peptidoglycan synthesis by interfering with enzymes called PBPs: penicillin-binding proteins
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5
Q

penicillins are bactericidal for what type of cells?

A

growing cells: only bactericidal for those undergoing cell-wall synthesis

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6
Q

what has a faster rate of kill activity: penicillins or fluoroquionolones

A

fluoroquinolones

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7
Q

how are beta-lactams bactericidal?

A

the ring of betalactams has a 3D structure that mimics a terminus that acts as a natural substrate for transpeptidase activity during cell wall synthesis
- by blocking the formation of theses covalent bonds, the cell weakens and leads to lysis from high internal osmotic pressure

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8
Q

what determines if beta lactams will be effective on cells?

A

variation in activity for Gram + vs Gram - depends on:
- differences in receptor sites on PBPs
- relative amount of peptidoglycan present
- ability to penetrate outer cell membrane of Gm-
- resistance to different types of betalactamase enzymes present

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9
Q

bactericidal of beta-lactams is dependent on

A

time

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10
Q

are beta lactams time or concentration dependent?

A

time dependent: length of time that abx concentrations at site of infection exceed the MIC (T>MIC) should be at least 50-60% of the dosing interval)
- thus, these drugs are often dosed MORE FREQUENTLY than the concentration dependent drugs like fluoroquinolones

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11
Q

you need to give Muffin, a 9 year old crusty white dog, antibiotics. You decide on a beta lactam, and because you are an astute CSU grad, you know that these drugs are time-dependent. what does this mean for how often you are likely going to dose Muffin?

A

muffin will likely be dosed more frequently because of the time-dependency: need to be above the MIC to constantly block the transpeptidase in cell wall formation

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12
Q

why is the “eagle” or paradoxical effect important with beta lactams?

A
  • if you give concentrations above an optimal killing concentration, you get reduced bactericidal (killing) effect because PBPs get bound and cause a growth arrest. this failure to grow means failure to be killed by the antibiotic
  • important because there can be a tendency to overdose with these drugs due to the large margin of safety. more doesn’t always mean better!!
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13
Q

resistance to beta-lactam abx

A
  • beta lactamase enzymes produced by bacteria
  • these enzymes break the beta-lactam ring, destroying the active part of the drug
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14
Q

where do gram + produce beta lactamases?

A

gram + produce inducible beta-lactamase extra-cellularly

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15
Q

where do gram - bacteria produce beta lactamases?

A

constitutively produce beta-lactamase in the peri-plasmic space

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16
Q

gram - bacteria beta lactamase enzymes are more active against what drugs?

A

penicillins

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17
Q

what is better at killing gram - bacteria: penicillins or cephalosporins?

A

cephalosporins: the beta lactamase enzymes are more active against penicillins than cephalosporins

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18
Q

why has the discovery of beta-lactamase inhibitory drugs been so important

A

they irreversibly bind the beta-lactamase enzyme and allow the antibiotic to exert the bactericidal effect: we use these with beta-lactams to block the bacteria’s ability to break down the drug

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19
Q

what beta-lactamase enzyme inhibitors are often mixed with beta-lactam antibiotics?

A

avibactam, clavulanic acid, tazobactam
best way to block resistance via b-lactamase enzymes is to inhibit them!

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20
Q

are penicillins well or poorly absorbed orally?

A

poorly absorbed orally

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21
Q

why are penicillins often given frequently?

A

they have very short half lives/rapid elimination = frequent administration + slowly absorbing formulations like procaine penicillin has helped combat this

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22
Q

PK properties of penicillins

A
  • acid labile, poorly absorbed orally
  • short half-lives/rapid elimination
  • small volume of distribution, don’t cross membranes easily
  • eliminated almost entirely through renal excretion = very high urine concentrations
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23
Q

why would you not want to use penicillins for a intracellular bacterial infection/mycoplasma?

A

penicillins have a very small volume of distribution and do not cross biologic membranes readily. they are very water soluble and are limited to extra-cellular water

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24
Q

how are penicillins eliminated?

A

almost entirely through renal excretion = very high urine concentrations. don’t really need to worry about giving to renally impaired patients because of the wide margin of safety

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25
Q

natural penicillin

A

benzyl penicillin and long-acting parenteral forms

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26
Q

penicillin G activity

A

most active against Gm+ aerobes and anaerobes
less activity against Staph, Gm- and enterobacter are generally resistant

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27
Q

is penicillin G more active against Gm + or Gm- bacteria?

A

Gram + aerobes and anaerobes

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28
Q

toxicities of penicillin G

A

rare, but most often is hypersensitivity reaction, can cause anaphylaxis
can have toxic effects from the potassium combined, esp if large amts of potassium PenG are injected rapidly: cardiac arrest

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29
Q

orally absorbed penicillins

A

penicillin V resists acid hydrolysis and is administered orally. same spectrum as benzyl penicillins

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30
Q

Penicillin G Salt Forms

A

IV or IM use

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31
Q

Penicillin V tablets

A

oral use (acid stable)

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32
Q

Penicillin G- Benzathine Salt Suspension

A
  • IM
  • slow release due to solubility
  • lower peak, longer duration in plasma
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33
Q

penicillin G- Procaine Salt Suspension

A
  • IM
  • slow release due to solubility
  • lower peak, longer duration in plasma
  • local anesthetic activity of procaine may alleviate deep muscle pain associated w drug
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34
Q

why would administering procaine salt suspension of Pen G help with pain?

A

it has local anesthetic activity: may alleviate deep muscle pain associated with drug

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35
Q

what type of penicillin should you NOT use in exotic species?

A

procaine penicillin!! susceptible to procaine toxicity!!

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36
Q

what species should you NOT use procain penicillin in?

A

birds, snakes, turtles, guinea pigs, chinchillas
susceptible to procaine toxicity!!!

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37
Q

aminopenicillins

A

ampicillin + amoxicillin

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38
Q

why are aminopenicillins considered extended-spectrum?

A

spectrum of activity is increased to include many Gram- aerobes (E.coli, Proteus, Pasteurella)

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39
Q

spectrum of activity of ampicillin and amoxicillins

A
  • spectrum increased to include many Gm- aerobes (E. coli, Proteus, Pasteurella)
  • slightly less activity than PenG against Gm+ and anaerobes, but still useful clinically
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40
Q

what has more bioavailability, amoxicillin or ampicillin?

A

amoxicillin (70% > 40%)

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41
Q

why are aminopenicillins often combined with beta-lactamase inhibitors?

A

they are susceptible to beta-lactamase hydrolysis
- combos with inhibitors like clavulanic acid, sulbactam or tazobactam increase their effectiveness considerably

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42
Q

antistaphylococcal penicillins

A

cloxacillin, dicloxacillin, oxacillin, methicillin

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43
Q

why are the antistaphylococcal penicillins useful?

A

resistant to the beta-lactamases produced by Staph aureus! mainly used in treatment of bovine staphylococcal mastitis

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44
Q

you get called out to a dairy farm for a couple cases of mastitis. you are suspecting they are staphylococcal in origin. if you were to reach for antibiotics, what might be some options?

A

antistaphylococcal: cloxacillin, dicloxacillin, oxacillin, methicillin

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45
Q

what antistaph abx can be given orally to monogastrics?

A

cloxacillin and oxacillin

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46
Q

what is oxacillin used to test for?

A

methicillin sensitivity in vitro

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47
Q

methicillin resistant staphylococcus (MRSA and MRSP) can be considered resistant to

A

ALL beta lactam antibiotics. have super strong beta lactamases

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48
Q

what causes methicillin resistance?

A

the MecA gene in bacteria producing an alternative PBP (PBP2A)

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49
Q

antipseudomonal/extended spectrum penicillins

A

carbenicillin, ticarcillin, piperacillin

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50
Q

what is unique about drugs like carbenicillin, ticarcillin, piperacillin?

A

they are defined by their superior activity against Pseudomonas, which none of the other penicillins have
- cost and requirement for IV delivery may limit utility

51
Q

what may limit utility of antipseudomonal/extended spectrum abx?

A

cost and requirement for IV delivery

52
Q

what antipseudomonal drug has been used for treatment of otitis externa in dogs?

A

ticarcillin IV has been used in combo w topical ticarcillin in treatment of otitis externa in dogs caused by Pseudomonas aeruginosa

53
Q

do you use beta-lactamase inhibitors with antipseudomonals?

A

yes! they are susceptible to inactivation by beta-lactamase enzymes and thus can be combined with beta-lactamase inhibitors

54
Q

ticarcillin + clavulonic acid

A

Timentin

55
Q

Piperacillin + Tazobactam

A

Tazocin

56
Q

carbenicillin, ticarcillin, and piperacillin are all what type of abx?

A

beta-lactams, penicillins, antipseudomonal/extended spectrum

57
Q

what are potential issues with extended spectrum penicillins?

A

potential for disturbing normal intestinal flora
- after oral administration in dogs and cats this effect is less marked with amoxicillin than ampicillin because of better absorption (less drug remaining in GI tract)
- ampicillin should NOT be administered to small rodents (guinea pigs, gerbils, hamsters) or rabbits since it may produce Clostridial colitis

58
Q

what is better to use in dogs and cats, amoxicillin or ampicillin?

A

amoxicillin! less drug remaining in GI tract, better absorption and less disturbance of normal intestinal flora

59
Q

what drug should NOT be administered to small rodents or rabbits since it may produce Clostridial colitis?

A

ampicillin!

60
Q

why should ampicillin not be administered to small rodents and rabbits?

A

it may produce Clostridial colitis :(

61
Q

what is the best penicillin for treatment of urinary tract infections?

A

amoxicillin

62
Q

what is the drug of choice for treating leptospirosis

A

amoxicillin

63
Q

what are the drugs of choice for mixed aerobic-anaerobic infections like cat-bite infections?

A

ampicillin or amoxicillin

64
Q

cephalosporins

A

beta lactam ring is attached to a 6 membered ring which makes this class inherently more resistant to beta-lactamase enzymes
- originally made for txt of penicillinase-producing staph infections

65
Q

what came first, cephalexin or cefazolin?

A

cephalexin: ones discovered before 1975 are spelled with ph and ones after 1975 are spelled with f

66
Q

PK of cephalosporins

A
  • generally similar typical of beta lactams
  • usually require parenteral injection
  • short half-lives for most, needing frequent administrations (w a few exceptions)
  • usually excreted thru kidneys into urine
  • widely distributed to extracellular fluids and tissues EXCEPT CNS and eye
  • poor intracellular penetration = low volume of distribution
    TIME DEPENDENT AND BACTERICIDAL
67
Q

are cephalsoporins bacteriostatic or bactericidal?

A

bactericidal

68
Q

are cephalosporins time dependent or concentration dependent?

A

time dependent

69
Q

what is a good alternative for penicillin-sensitive individuals?

A

cephalosporins
- time dependent, bactericidal activity, relatively non-toxic

70
Q

antimicrobial activity of cephalosporins

A

varies with successive “generations”
- in general, as generation # increases (1-4), the Gram- coverage increases but at the cost of Gram+ coverage

71
Q

what would have more gram - coverage: a 1st generation cephalosporin or a 4th generation cephalosporin?

A

4th generation

72
Q

1st generation cephalosporins have similar spectrum of activity to what abx?

A

aminopenicillins: amoxicillin and ampicillin

73
Q

how does cephalosporin resistance happen?

A

same mechanisms as for penicillins
- PBP modification
- reduced permeability and increased efflux
- beta-lactamase production: most important mechanism!!

74
Q

first generation cephalosporins

A
  • good activity: Gram + aerobes, including beta-lactamase producing staph and strep
  • moderate: Gram - Enterobacteriacea
  • NO activity against Pseudomonas or Enterobacter
75
Q

what do first generation cephalosporins have good activity against?

A

gram + aerobes, including beta lactamase producing staph and strep

76
Q

what are the injectable formulations of first generation cephalosporins?

A

cefazolin, cephapirin, cephalothin

76
Q

what are oral formulations of first generation cephalosporins?

A

cephalexin and cefadroxil

77
Q

what do all 2nd generation cephalosporins have in common?

A

they are all given parentally! NO ORAL FORMULATIONS

77
Q

clinical applications of first generation cephalosporins

A

skin and urinary tract infections and other nonspecific infections caused by staph, strep, enterobacteria and some anaerobes

78
Q

cefazolin and cephalexin are what type of abx?

A

first generation cephalosporin

79
Q

antimicrobial activity of 2nd generation cephalosporins

A
  • slightly more gram - and anaerobe coverage than 1st gen
  • slightly less gram + coverage than 1st gen
80
Q

where are 2nd generation cephalosporins derived from?

A

2 rugs are derived from streptomyces rather than cephalosporium

81
Q

what is unique about the cephamycins: cefotetan and cefoxitin?

A

they are very stable to beta-lactamases! including those of bacteroides

82
Q

clinical applications of 2nd generation cephalosporins

A
  • cefoxitin can be used for aspiration pneumonia, bite infx, peritonitis, colonic surgery (mixed infections)
  • cefuroxime for dry-cow therapy and for treatment of clinical mastitis in lactating cattle
83
Q

how are 2nd generation cephalosporins given?

A

PARENTALLY! no oral formulations!!

84
Q

3rd generation cephalosporins activity

A
  • extended activity against Gm- pathogens
  • some have good activity against Pseudomonas: Ceftazidime has best
  • more resistant to beta lactamase enzymes
85
Q

examples of 3rd generation cephalosporins

A

cefovecin, cefoxatime, ceftiofur

86
Q

ceftiofur is what type of abx?

A

3rd generation cephalosporin

87
Q

what is ceftiofur used for?

A

respiratory disease of cattle, sheep, swine, horses, and urinary tract infection of dogs

88
Q

cefovecin

A

CONVENIAAAA

89
Q

what type of drug is convenia?

A

3rd generation cephalosporin: Cefovecin is a SQ formulation for dogs and cats that can be used as a single treatment: drug levels remain above MIC for Staph pseud for 14 days
half-life in dogs and cats is about 5 1/2-7 days

90
Q

oral 3rd generation cephalosporins

A

cefpodoxime (Simplicef)

91
Q

cefpodoxime

A
  • 3rd generation cephalosporin
  • pro-drug that is deesterified in GI tract to release active cefpodoxime
  • longer halflife than other oral cephalosporins, allows for once a day dosing!
92
Q

T/F: cefpodoxime and cefovecin are active against pseudomonas

A

FALSE. even though they are 3rd gen cephalosporins they are not active against Pseudomonas

93
Q

what are cefpodoxime and cefovecin not active against?

A

Pseudomonas
even tho they are 3rd generation

94
Q

what should you NOT use for uncomplicated infections?

A

3rd and 4th generation cephalosporins! abx should be chosen that have the narrowest spectrum of activity needed for the infecting agent

95
Q

most cat bite infections can be successfully treated with

A

amoxicillin

96
Q

most staph skin infections can be treated with

A

cephalexin

97
Q

why do you not want to use 3rd and 4th generation cephalosporins all the time?

A

they have the ability to induce “super beta-lactamases” in bacteria that render them super resistant! and thus no beta-lactam may be effective. THIS IS SUPER BAD
- extended spectrum beta-lactamases are a big concern for human health and txt of serious gram-neg infections

98
Q

there is a ban on what abx in food animals?

A

extralabel cephalosporins: 3rd and 4th gen have ability to induce super beta lactamases

99
Q

carbapenems

A
  • beta lactam
  • derivative of Streptomyces spp and differ slightly from penam penicillins in structure
  • WIDEST ACTIVITY of any abx (exception is a fluoroquinolone)
100
Q

carbapenems activity

A

active against almost all clinically important aerobic or anaerobic Gm+ or Gm- cocci or rods
indv species such as MRSA/MRSP may have some resistance
- resistant to almost all bacterial beta-lactamase enzymes

101
Q

how are carbapenems administered?

A

all are administered parentally; IV, SQ, IM

101
Q

what are carbapenems role in human medicine?

A

“last resort” = super broad spectrum and wide activity

102
Q

imipenem

A
  • carbapenem
  • rapidly hydrolyzed in renal tubules to a NEPHROTOXIC COMPOUND
  • therefore ALWAYS administered with cilastatin to inhibit the enzyme that converts it and thus prevents nephrotoxicity
103
Q

how is imipenem administered?

A

IV only

104
Q

what is imipenem always administered with? why?

A

always administered with cilastatin because imipenem by itself gets hydrolyzed by a dehydropeptidase in the renal tubules to a nephrotoxic compound. cilastatin inhibits the dihydropeptidase

105
Q

cilastatin is always administered with what drug?

A

imipenem! a carbapenem

106
Q

what is impenem used for?

A

primarily for treatment of ESBL: extended spectrum beta lactamase expressing bacteria when a single drug is required (3-4 doses per day required)

107
Q

morepenem

A

carbapenem, sometimes used off-label: ex IV product can be used SQ with similar activity to imipenem

108
Q

how does cilastatin work

A

blocks formation of a toxic metabolite and thus prevents nephrotoxicity of imipenem

109
Q

what is dangerous about using carbapenems?

A

They have such broad-spectrum bactericidal action that bacterial superinfections with resistant bacteria are a likely sequela which will lead to contamination of the environment with such naturally resistant bacteria.

110
Q

if using carbapenems for Pseudomonas, what should you combine them with? why?

A

combine with an aminoglycoside to reduce potential for resistance

111
Q

monobactams

A
  • aztreonam
  • stable to most betalactamase enzymes
  • use is mainly as substitute for more toxic aminoglycoside in combo therapy of severe mixed infx (ex w clindamycin or metronidazole for mixed infc)
112
Q

spectrum of activity of monobactams

A

almost all gram - aerobic bacteria
- resistance seen in Gm+ and anaerobes

112
Q

aztreonam

A

only monobactam drug evaluated in vetmed

113
Q

classification of beta lactams

A
  1. Class of microorganism to which they show activity * Bacteria
  2. Antibacterial spectrum of activity
    * Gram+
    * Gram- (varied across the class)
  3. Bacteriostatic or bacteriacidal
    * Bacteriacidal
    * Bacteriostatic at too high a concentration (paradoxical effect)
  4. Time or concentration-dependent activity
    * Time-Dependent (T>MIC)
114
Q

are beta lactams bacteriostatic or bactericidal?

A

bactericidal

115
Q
A
116
Q
A
117
Q
A
118
Q
A
119
Q
A

Pharmacology Final (9 decks)

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