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Pharmacology > Beta-lactams > Flashcards

Beta-lactams Flashcards

1
Q

Beta-lactams

A

-includes penicillins and cephalosporins

-all have a beta lactam ring which is site of action of penicillinase

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2
Q

Benzyl penicillin vs. Penicillin G

A

The exact same thing, just two different names

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3
Q

Crystalline penicillin G

A

-Na or K salt with penicillin

Formulations:
1.sterile formulations for injection (IV formulation, sometimes IM, SC)
2. Soluble powder for drinking water- in Vet med

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4
Q

Procaine Penicillin G

A

-used commonly in cattle and horses
-Short acting/daily injections procaine will slow down penicillin absorption
-give IM or SQ; NEVER IV

Formulations:
-white injectable penicillin
-oral feed premixes

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5
Q

Benzathine Penicillin G

A

-long acting injectable penicillin (IM, some products are IV)
*not absorbed well

-Only in Duplocillin in Canada for LA

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6
Q

Penicillin V

A

-acid stable so can be given orally
-not really used in vet med, other drugs are better

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7
Q

Procaine Pen G in oil

A

-long acting
-IM or SC only

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8
Q

Procaine and benzathine Pen G formulation

A

-long acting
-IM or SQ injection only

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9
Q

Penicillin G Mechanism of Action

A

Act by disrupting synthesis of bacterial cell wall
-inhibits the penicillin-binding proteins (PBPs) on outside of bacterial cell membrane
-this interferes with enzymes (transpeptidases) needed for peptidoglycan synthesis (part of cell wall)
-causes lysis of growing bacterial cells

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10
Q

Are penicillin G a bactericidal or bacteristatic?

A

Bactericidal- BUT only if bacteria is actively growing

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11
Q

What types of bacteria does Penicillin G get used for?

A

GRAM +
-lots of peptidoglycan in cell wall
-high affinity of PBPs for beta-lactams

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12
Q

Why does penicillian not work as well for gram - ?

A

-lesser peptidoglycan in cell wall and lower affinityof PBPs for beta lactams

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13
Q

What are possible resistance mechanisms of bacteria against Penicillin G?

A

-Presence of penicillinase (exogenous often gram + which breaks down Penicillin) or Beta-lactamase enzymes (exogenous often gram - which break down penicillin)

-inability of Beta-lactam to penetrate bacterial cell wall

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14
Q

Cephalosporin and penicillinase or beta-lactamases

A

Cephalosporin can make it through the enzymes and bacteria will be susceptible

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15
Q

Penicillin G spectrum activity

A

-Many gram + (mostly strep, not most staph because they make beta-lactamase)

-Many anaerobes

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16
Q

MIC numbers and penicillins

A

MIC values are great and comparing susceptibility

ex. Low number= will kill it off

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17
Q

Bacteria you can use Penicillin G for

A

Gram +
-Actinomyces
-Trueperella pyogenes
-Some Bacillus anthracis, Corynebacterium, Erysipelothrix, rhusiopathiae, Listeria

Gram -
-Some histophilus, pasteurella

-most anaerobes
-fusobacterium, some clostridium, some bacteroides

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18
Q

Bacteria typically resistant to Penicillin G

A
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19
Q

Penicillin Oral Pharmacokinetics

A

-poor oral absorption of Pen G due to rapid hydrolysis in stomach acid
**Exception: Phenoxymethyl penicillin

-Pen G used in feed premix or drinking water BECAUSE not trying to get plasma concentrations, just for local effects in GI tract

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20
Q

Penicillin Parenteral Pharmacokinetics

A
  1. Crystalline pen G
    -only dosage used IV. Rapid absorption after IM or SC]
    -need every 6 hrs; high concentration but drops quickly
  2. Procaine pen G
    -slowly absorbed IM then crystalline forms
    -causes vasoconstriction at injection site
    -lower but sustained plasma concentrations
    -absorbed more and quicker in neck then in hindquarters (also less carcass damage)
    -NEVER IV because CNS signs
    **milky= no IV
  3. Benzathine pen G
    -poorly soluble, very slowly absorbed
    -produces sustained Pen G plasma concentration but not high enough to reach MIC= residues in meat and milk
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21
Q

Distribution of Penicillin

A

-Weak acid (pKa= 2.7)
-highly ionized at physiological pH/plasma?

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22
Q

Penicillin Volume of distribution

A

-Low VD
- will stay in plasma and extracellular fluid (honestly good because other infection is in the ECF)
-Some tissues may not get therapeutic conc, BUT increased distribution to tissues with inflammation

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23
Q

Penicillin elimination and excretion

A

Elimination: Very little metabolism

Excretion: Renal (some GFR, some into renal tubule)
*no real need to adjust dose for renal disease

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24
Q

Penicillin half life

A

1-2 hours
But variation depending on the formulations. Procaine/Benzathine forms will take longer because takes longer to absorb

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25
Q

Penicillin as Time dependent antimicrobials

A

-efficacy not based on high Cmax
-Keep penicillin conc >MIC for as long as possible

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26
Q

Dosing for Penicillin formulations

A

-Crystalline penicillin: may need TID/QID

-Procaine Pen G: once daily dosing

-LA procaine/benzathine Pen G: days between doses BUT Flip flop kinetics (prolonged absorption so longer half life)

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27
Q

Adverse rxns of Penicillin

A
  1. Hypersensitivity (from R1 side chains, not beta-lactam ring)
    -anaphylaxis/ local inflammation (Type I)
    -Autoimmune hemolytic anemia (Type II)
    -Vasculitis (Type III)
  2. GI flora changes (diarrhea)
    -especially in hindgut fermenters (horses, rodents, rabbits)
  3. Drug residues in food animals
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28
Q

Beta lactam drug interaction

A

-Beta lactams disrupt the bacterial cell wall which can increase aminoglycoside antimicrobial entry into the bacterial cell
**little clinical relevance that synergism results in better outcomes BUT benefits because they have complementary range of microbial targets

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29
Q

Cloxacillin

A

-Anti-staphylococcal penicillin (Isoxazolyl- eg. methicillin but not used)
-active against same bacteria as Pen G BUT are resistant to Staphylococcus penicillincase enzyme

**used to treat or prevent bovine staphyloccocal mastitis

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30
Q

MRSA or MRSP

A

-resistant to methicillin (Staph aureus and Staph pseudointermedius)

*has mecA gene which codes for PBP2A which is different from regular PBP
=low affinity for all beta-lactam drugs= RESISTANCE

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31
Q

Antistaphylococcal penicillins

A

-used against many gram positives (including most staphs)
AND anaerobes

32
Q

Aminopenicillins

A

-Includes ampicillin and amoxicillin

33
Q

Ampicillin formulations

A

1.Polyflex: Trihydrate salt injectable suspension (white and milky)
-IM, SC in cattle, swine, dogs, and cats (not really dogs and cats)

  1. Human sterile crystalline Na
    -IV injectable or oral
34
Q

Amoxicillin formulations

A
  1. Many vet oral tablets/suspensions
    *often includes clavulanic acid
    -used in dogs and cats
  2. Soluble powder for medicated water
    -used in swine and poultry
35
Q

Aminopenicillin spectrum of activity

A

-active against all bacteria that Pen G is (comparable potency)

-amino groups allow for better penetration through the outer layer of gram negative bacteria than penicillin G (especially amoxicillin)

36
Q

What are aminopenicillins susceptable to?

A

Still susceptible to degradation by microbial beta-lactamase/penicillinase enzymes
*same as Pen G

37
Q

What are aminopenicillins used for?

A

1.some gram negatives

  1. Anaerobes
  2. Many gram positives except most staphs
38
Q

Aminopenicillin absorption

A
  1. Oral
    -acid stable
    -60-80% bioavailability (ampicillin is half amoxicillin)
    -amoxicillin can give with food or without. Check labels though
  2. Injectable
    -Ampicillin trihydrate= slow absorption SC and IM
    -Ampicillin sodium= rapid, can be given IV
39
Q

Aminopenicillin distribution, metabolism, excretion

A

same as Pen G

40
Q

Dosing of Aminopenicillins

A

-BID dosing for oral forms

-SID for ampicillin trihydrate (Polyflex) after IM injection
*slower absorption so prolonged plasma concentrations

41
Q

Aminopenicillin drug interactions

A

-synergy with aminoglycosides in terms fo spectrum activity

42
Q

Adverse events for aminopenicillin

A
  1. Hypersensitivity
    -slightly less than Pen G
    -cross reactivity between Pen G and aminopenicillins is less than 5%
    -Cross reactivity between some cephalosporins
  2. Oral adverse events= vomiting and diarrhea
43
Q

Anti-pseudomonal penicillins

A

Piperacillin
-all human formulations
-given IV, with a beta lactamase inhibitor like tazobactum
-costly

44
Q

Anti-pseudomonal penicillin spectrum of activity

A

-active against gram negatives (except beta-lactamase producers)

-active against pseudomonas (penetrates cell walls)

-active against anaerobes

**note: no activity against gram positives

45
Q

Clavulanic acid

A

-Beta-lactamase inhibitors

-many oral tablets and suspensions for small animals= clavamox, clavaseptin, aventiclav

*human formulations have a different ratio of Amox:Clav

46
Q

Beta-lactamase inhibitors mechanism of action

A

-little antimicrobial activity on its own
-But does irreversibly bind to and inactivate beta-lactamase enzymes. Allows beta lactam antimicrobial included in the formulation to bind with PBP

47
Q

Beta-lactamase inhibitors spectrum of activity

A

WHEN INCLUDED WITH AMOXICILLIN

-most gram positives including most beta-lactamase producing staph (unless methicillin resistant because different PBP)

-many gram negatives

-many anaerobes

48
Q

Beta-lactamase inhibitors

A

-quick absorption orally

-renal excretion

-Half life similar to amoxicillin

-minimal adverse effects. Effects would likely be due to aminopenicillin part of drug combo

49
Q

Imipenem or Meropenem (CARBAPENEMS)

A

-extended spectrum
-should very rarely be used in vet med because they are critical drugs for human med

50
Q

Carbapenems spectrum of use

A

-gram +
-gram -
-anaerobes

**Works well because impervious to beta-lactamase enzymes
BUT dont use because last resort in human med

51
Q

Cephalosporins

A

-part of beta-lactam family
-older generation is narrow spectrum or less administration routes

52
Q

Cephalosporin vet formulations

A
  1. Cephalexin (Rilexine or Cefaseptin tablets)
  2. Ceftiofur
    -Excenel (Na salt)
    -Excenel RTU (HCl)
    -Excede (crystalline free acid)
    -Spectramast (intramammary)
  3. Cefovecin (convenia injectable)
  4. Cefpodoxime (simplicef tabs)
  5. Cephapirin
    -Cefa-Lak (Na)
    -Cefa-dry, Metricure (benzathine)
53
Q

Cefazolin

A

-not a vet product BUT human sterile injectable formulation used in small animal clinics typically around surgery

54
Q

Ceftiofur sodium

A

used in cattle, horses, pigs, sheep

55
Q

Ceftiofur HCl

A

-milky
-long lasting
-Not IV
-cattle and pigs

56
Q

Ceftiofur crystalline fre acid

A

-slow release
-cattle and horses

57
Q

Cephalexin

A

-now only oral tablets
-often indicated for superficial pyoderma caused by staphylococcus pseudintermedius

58
Q

Convenia in dogs for skin

A

-for bacterial folliculitis, wounds, abscesses caused by susceptible strains of Staphy intermedius, Strep Canis, and e coli

59
Q

Convenia for UTIs in dogs

A

UTIs associated with e coli and proteus mirabilis

60
Q

Convenia used in cats with skin infections

A

-used for abscessed, wounds caused by P. multocida, Prevotella bivia, Bacteroides fragilis, Staph intermedius

61
Q

Cefazolin

A

-used prior to surgery
-studies show small reduction in post op infection

62
Q

Compounded Ceftiofur sodium biobullets

A

Horrible idea
-compounded product
-shooting animal
-bullets are 100mg so need to shoot them 5 x
-injection site lesions
-potential for drug residues

63
Q

Cephalosporin mechanism of action

A

-same as penicillins… disrupt synthesis of bacterial cell walls by inhibiting penicillin binding proteins

*stable against some beta-lactamase enzymes and good affinity for target proteins

64
Q

Resistance to Cephalosporins

A
  1. different beta-lactamase enzymes
    -extended spectrum beta lactamase enzymes
    -AmpC cephalosporinases
    -Metallo- beta- lactamase enzymes
  2. Modify PBPs
    -mecA gene or others
  3. Reduce cellular concentrations
    -decrease bacterial cell wall permeability
    -induction of efflux pumps
65
Q

Cephalosporins spectrum of activity

A
  1. Gram +
    -Strep species
    -staph aureus, pseudintermedius
    -many other gram + (but does not mean more susceptible to cephalosporins than to penicillins)

2.gram -
-e coli, salmonella, klebsiella
-histophilus, Mannheimia, Pasteurella

3.most anaerobes

66
Q

What bacteria are resistant to cephalosporins?

A

Gram +
1. Methicillin resistant staph
2. Enterococcus KNOW THIS

Gram-
1. many enteric pathogens with ESBL activity
2. Rhodococcus equi
3. Pseudomonas
4. Mycobacteria

Bacteroides (anaerobe)
*except cefoxitin

67
Q

Cephalosporins PK orally

A

Good Oral absorption

-Simplicef (cefpodoxime proxetil)= prodrug which goes through GI track and is de-esterfied allowing for cefpodoxime to be absorbed

-give with food to minimize GI effects, but also saw slight increase in bioavailability

68
Q

Cephalosporin PK parenterally

A

*depends on formulation

  1. Cefazolin- rapid, can be given IV
  2. Ceftiofur sodium (Excenel)- very rapid, can go IV but only labeled for IM/SC
  3. Ceftiofur HCl (Excenel RTU EZ (ready to use; less viscous material)- SID, slower
  4. Ceftiofur crystalline free (Excede)- given at base of ear, very slow, long lasting
69
Q

CEphalosporin distribution

A

Low Vd

70
Q

Cephalosporin metabolism

A

Some metabolites produced for some of the drugs
-but not a concern for liver
-also most metabolites still work same way as drug

71
Q

Cephalosporin elimination

A

renal
-glomerular filtration and tubular secretion

**not a concern for patients with kidney failure

72
Q

Cephalosporin half lives

A

Generally short (1-2hrs) EXCEPT:

  1. Cefpodoxime and Cefovecin
    -highly protein bound
  2. Cefpodoxime
    -5-6hrs
    -SID with simplicef
  3. Cefovecin (convenia)
    -5.5-6.9 days after SC in dogs and cats
    -low clearance in kidney because high protein binding
    -one dose every 2 weeks
    *need to ensure MIC is high enough
73
Q

Ceftiofur half life variation for different half lives

A
  1. Ceftiofur sodium= Excenel - 2-3hrs for cattle
  2. Ceftiofur HCl=Excenel RTU
    -20hrs in pigs
  3. Ceftiofur crystalline free acid= Excede
    -40+hrs in cattle
    -50hrs in pigs
74
Q

Excede administration

A

-given at base of cows ear

-no drug residues but risk if it went into the auricular artery because will get into the CNS

75
Q

Adverse effects of cephalosporins

A
  1. Hypersensitivity
    -low cross reactivity between cephalosporins and penicillin
    -higher cross reactivity between older cephalosporins with aminopenicillins
  2. GI upset
    -vomit
    -loss of normal GI flora leading to bacterial overgrowth= Superinfection (C. diff overgrowth)
  3. Nephrotoxicity (RARE)
  4. Coagulopathies/blood dyscrasias (RARE)
    -low platelets
76
Q

Concerns with cephalosporin use (FDA) driving Antimicrobial resistance

A

No extralabel administration in food animals meaning:
-cant alter the dose, route, frequency, or duration
-can’t use for prevention

Can use extralabel in minor species (Sheep, alpacas) and for different indication

**note health canada cannot ban these things the same way

77
Q

Vancomycin-resistant enterococci

A

Inherent resistance to cephalosporins
-risk factors: hospital stays, intensive care units, transplants, hematologic malignancies, exposure to antibiotics

Pharmacology (37 decks)

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