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General Pharmacology 2 > Antimicrobial Therapy: Beta-Lactams > Flashcards

Antimicrobial Therapy: Beta-Lactams Flashcards

1
Q

Beta-Lactams

A
  • Drug class characterized by the Beta-Lactam ring
    • penecillins, cephalosporins, carbapenems
    • Beta lactamase inhibitors
  • Sir Alexander Fleming discovered by mistake
    • staphylococcus plate contaminated with penicillium mold which inhibited staphylococcus growth
    • Initially ~ 10 years scientific community brushed it off as umimportant … it is not very stable, hard to isolate/mass produce, and why do we need it?
    • A team of scientists discovered methods to isolate, stabilize, purify and mass produce
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2
Q

Beta-Lactams:

Pharmacodynamics

A

MOA: Bind to penicillin binding proteins, enzymes in peptidoglycan biosynthesis in the bacterial cell wall, resulting in cell wall failure

Bactericidal, T>MIC mostly

Weak acids

Variable oral absorption

Variable lipophilicity/penetration into protected environments

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3
Q

Beta-Lactams:

Resistance

A
  • Beta Lactamases -
    • break down beta lactam ring and inactivate drug
    • Penicillinases -
      • inactivate penicillins
    • Cephalosporinases -
      • inactivate some penicillins and cephalosporins
    • Extended Spectrum Beta Lactamases -
      • uh oh!
      • inactivate most beta lactams, but carbapenems may still be active
    • Carbapenemases -
      • inactivate carbapenems - oh no!
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4
Q

Beta-Lactams:

Resistance:

How do we treat these?

A
  • Penicillinases:
    • use cephalosporin for staphylococcus
  • Cephalosporinases:
    • use a beta lactamse inhibitor, or later generation cephalosporin
  • ESBLs, Carbapenemases:
    • consult a clinical pharmacologist or infectious disease expert, cross your fingers, and wear gloves
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5
Q

Beta Lactams:

Resistance:

Alterations in Penicillin binding Protein

A
  • No place for beta lactams to bind
  • Confers resistance across essentially the entire beta lactam class
  • If resistance ot oxacillin than resistance to all beta lactams regardless of MICs to specific beta lactams
    • E.g. Methicilin resistant Staphylococcus aureus (MRSA), Methicillin resitant Staphylococcus Pseudintermedius (MRSP)
  • How do we treat these?
    • many still susceptible to ather anitmicrobials
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6
Q

Penecillin Formulations:

Penicillin G

A
  • AKA: benzylpenicillin
  • Unstable in acid, no PO administration
  • Primary Spectrum:
    • gram positive and anaerobes
    • Efficacy: T>MIC
  • Poor lipophilicity and penetration into protected environments, although inflammation may enhance penetration
  • Weak acids (ion trapping)
  • Low protein binding
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7
Q

Penicillin Formulations:

Procaine Penicillin G

A

water insoluble, slow release from injection site, IM/SQ only

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8
Q

Penicillin Formulations:

Potassium Penicillin G

A

Water soluble, rapid absorption, can be administered IV

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9
Q

Penicillin Formulations:

Penicillin V

A

is available and is acid stable (po) but essentially never used

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10
Q

Penicillins:

PenG

A
  • primarily eliminated in the urine as active drug
  • Anaphylaxis si a possibility, but overall rare
  • May cause fatality in non-ruminant herbivores due to bacterial/clostridial overgrowth
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11
Q

Penecillins - Clinical Use:

Procaine Penicillin G

A
  • NEVER administer IV
  • Seizures can occur with inadvertant IV or potentially “free” prociane
  • Cattle:
    • rarely used due to widespread resistance.
    • PPG administer IM, not SQ due to hematoma formation and drug residue risk
  • Horses:
    • may cause racing violations due to prociane
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12
Q

Penicillin - Clinical Use:

Potassium Penicillin G

A
  • Most common IV
  • Horses:
    • give slowely
      • potential for potassium toxicity in cardiac arrhythmia and death
    • Also can stimulate GIT and result in defecation of soft feces
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13
Q

Penicillin - Clinical Uses

A

Pen G is overall well tolerated even with high doses

Effective for susceptible bacteria except in protected environments

Often used in conjunction with another antimicrobial

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14
Q

Aminopenicillins:

Amoxicillin

A
  • PO
  • More acid stable
  • some oral ampicillin formulations exist, but relative to amoxicillin ampicillin has much lower oral bioavailability
  • Some formulations for intrammary too
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15
Q

Aminopenicillins:

Ampicillin, Sodium

A
  • IV, IM, SQ
  • Can be administered PO, but amoxicillin preferred
  • Ampicillin trihydrate is an ampicillin suspension, but is more variable absorption
  • DO NOT ADMIN SUSPENSION IV
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16
Q

Aminopenicillins:

Enhance Spectrum

A

To include some gram negative, but resistant is often noted due to beta lactams

The “amino addition” enhances penetration into gram negative bacteria

Leptospira - can decrease circulating / shedding organisms, but will not eliminate infection

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17
Q

Aminopenicillins

A
  • Addition of beta lactamase inhibitor further enhances spectrum
    • irreversible antagonist of many, but not all, beta lactamases
    • Little anitmicrobial activity of beta lactamase inhibitors by themselves
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18
Q

Betal Lactamase Inhibitor:

Clavulanate / Clavulanic acid

A

oral beta lactamase inhibitor

Most commonly combined with amoxicillin

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19
Q

Beta Lactamase Inhibitor:

Sulbactam

A

injectable beta lactamase inhibitor

Most commonly combined with Ampicillin

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20
Q

Aminopenicillins:

Culture and susceptibility

A

ampicillin is typically the class represntative drug for amoxicillin

Amoxicillin / clavulanate is typically the marker drug for ampicillin / sulbactam

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21
Q

Aminopenicillins:

Species

A
  • most commonly used in small animal patients
    • Amoxicillin and ampicillin are well tolerated
      • Some GI adverse effects can occur uncommonly
      • Rare anaphylaxis
  • GI adverse effects in horses, poor PO bioavailability therefore not used
  • Typically not used in cattle
    • polyflex approved systemic, amoxi-mast appromed for IMM
  • Used in swine, waterers
  • Rabbits, Guinea pigs, rats etc. - PO use results in bacterial overgrowth and death
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22
Q

Anti-staphylococcal Penicillins

A
  • Specturm:
    • gram postivie aerobes and anaerobes
  • These drugs are resistant to beta lactamase
  • Used either intramammary or as markers for resistance
    • rarely used orally or systemically
      • cephalosporins much more widely used
23
Q

Anti-staphylococcal Penicillins:

Cloxacillin

A

intramammary

24
Q

Anti-Staphylococcal Penicillins:

Methicillin

A

was originally used ot test for PBP mediated resistance of Staphylococcus, but now Oxacillin is used

25
Q

Anti-pseudomonal Penicillins

A
  • Primarily parenteral, some topical
  • Used only for very resistant infections
    • Enterobacteriaceae including Pseudomonas
  • Used more commonly in exotic animal species
    • short half-life in birds, and dosing regimens may not be feasible
    • Snakes have longer half-life, more feasible
    • Also used in reptiles, amphibians, turtles, but little data supporting its use
26
Q

Cephalosporins

A
  • Originally isolated form a Fungus:
    • Acremonium aka “Cephalosporium”
  • Many additional drugs found / developed since originally isolated
27
Q

Cephalosporins:

MOA

A

SImialr to penicillins, binding to PBPs and bactericidal

28
Q

Cephalosporins:

Enhanced Spectrum

A

Cephalosporins are resistant to inactivation by the penicillinase beta lactamase and are therefore more active against those bacteria producing penicillinase

Stephylococcus are typically resisant to amoxicillin, but susceptible to cephalosporins

29
Q

Cephalosporins:

Efficacy

A

T>MIC

30
Q

Cephalosporins:

Resistance

A

there are other beta lactamases active against cephalosporins

Alteration of PBP also confers resistance to cephalosporins

MRSA are resistant to cephalosporins as well

31
Q

Cephalosporins:

Classification

A

There are many different ways to classify different cephalosporins, probably the most common way is by generations. Typically have some activity against anaerobes, but are not consistent for anareobes except cefoxitin

  1. First Generation:
    1. gram positive except Enterococcus,
    2. some gram negative
  2. Second Generation:
    1. additional activity against gram negative,
    2. some gram positive borrelia
    3. Cefoxitin has similar activity as 2nd gen, with good anaerobic spectrum
  3. Third Generation:
    1. Even greater activity agianst Gram negative, some penetrate BBB, some are lepto positive
    2. Ceftazidime is the only 1-3rd generation cephalosporin we use with activity against pseudomonas
  4. Fourth Generation:
    1. rarely used in vet med
    2. has activity against Pseudomonas and retains activity against some cephalosporinase producing bacteria
  5. Fifth generation:
    1. yeah, dont worry about these
    2. Not used in vet med
32
Q

Cephalosporins:

dosing

A

is drug specific, but oral, IV, IM, SQ, intramammary formulations are available depending on the specific drug

33
Q

Cephalosporin:

Distribution

A

most cephalosporins do not penetrate protected environments well

The primary exception are some 3rd generation cephalosporins

weak acids

protein binding varies from low to high

34
Q

Cephalosporin:

Elimination

A

most cephalosporins are primarily eliminated as unchanged drug in urine.

Therefore urine concentrations are typically very high

Ceftiofur is metabolized to desfuroylceftiofur, and active metabolite, after systemic administration and desfuroylceftiofur primarily eliminated in urine

35
Q

Cephalosporins:

Adverse Effects

A
  • PO can result in vomiting diarrhea
  • Anaphylactic reactions rare, but may cross react with penicillins
  • False positive coombs test for autoimmune disease
  • High doses of ceftiofur/cefuroxime associated with anemia, thrombocytopenia
  • Bleeding disorders have been reported in dogs, but quite rare
  • Many people avoid cephalosporins in patients with bleeding disorders, but overall risk is considered quite low for the cephalosporins used in vet med
  • Enhanced risk of seizure reported in predisposed dogs, although the risk seem quite low especially compared to other antimicrobials
36
Q

First Generation Cephalosporins:

Cephalexin

A

oral formulations

2-3x daily administration

In general, well tolerated

AE: vomiting, anorexia

Uses: skin and soft tissue infections, UTI, intraocular infections, osteomyelitis, perioperative as appropriate

37
Q

First Generation Cephalosporin:

Cefazolin

A

parenteral only

4-8 hour administration

Uses similar to cephalexin

38
Q

First Generatation Cephalosporin:

Cephapirin

A

Intramammary formulations

Two different formulations - be sure to use the correct one

39
Q

Second Generation Cephalosporins:

Cefuroxime

A

Rarely used PO (dogs)

Has some penetration into prostate and CNS

can be used as outpatient, but not as good as parenteral cefotaxime, ceftriaxone, or ceftazidime

Short Half-life, q6-8h dosing needed

High doses of cefuroxime associated with anemia, thrombocytopenia

40
Q

Second Generation Cephalosporins:

Cefoxitin

A

Rarely used

Actually a cephamycin

Will occasionaly be used for surgical prophylaxis for large intestine surgery or if anaerobic bacteria is suspected

41
Q

Third Generation Cephalosporins:

Cefpodoxime

A

PO, once daily administration

Labeled for use in dogs (skin), but used similar as cephalexin with better gram negative activity

NO activity against Pseudomonas

Does NOT penetrate protected tissue well

42
Q

Third Generation Cephalosporins:

Cefovecin

A

SQ>>IV

Once every 7-14 days in Small animals

Not a sustained release, but large plasma protein binding

Remember only unbound drug is active

NO activity against Pseudomonas

Does NOT penetrate protected tissues well

43
Q

Third Generation Cephalosporins:

Ceftiofur

A
  • Metabolized to desfuroylceftiofur which is primary active component for systemic administration
  • Susceptibility testing is based on ceftiofur though
  • Desfuroylceftiofur is less active agianst Staphylococcus compared to ceftiofur, so susceptibilty testing overestimates activity agianst Staphylococcus
  • Other bacteria have essentially the same susceptibility to ceftiofur and metabolite
  • Penetrate bronchi well, but NOT other protected environments
  • Labeled For:
    • UTI in dogs
    • BRD, foot rot (mastitis for IMM) in cattle
    • Respiratory disease in swine, goats, sheep
    • Strangles
    • Control in early mortality (chicks, poults)
  • Used extralabel for many other reasons
44
Q

Third Generation Cephalosporins:

Ceftiofur:

Sodium Ceftiofur

A

Naxcel

water soluble solution

Short shelf life (stable 7 days when refrigerated, 12 hours at room temp)

Labeled for beef and dairy cattle, swine, goats, sheep, horses, dogs, day-old chicks/turkey poults

45
Q

Third generation Cephalosporins:

Ceftiofur:

Ceftiofur hydrochloride

A

Excenenl RTU EZ

Suspension,

Shelf stable, use within 42 days of opening

Labeled for beed and dairy cattle, swine

46
Q

Third Generation Cephalosporins:

Ceftiofur

Ceftiofur hydrochloride (Spectramast)

A

Intrammary use - two formulation

Dry cow

Lactating cow

47
Q

Third Generation Cephalosporins:

Ceftiofur

Ceftiofur Crystalline Free Acid

A

Suspension

Shelf stable and sustained release

Use within 12 weeks of opening

Labeled for beef and non-lactating diary cattle, horses, swine

48
Q

Third Generation Cephalosporins:

Cefotaxime / Ceftriaxone

Uncommon use

A

Injection only

Good activity agianst gram negative and many gram positive

NOT pseudomonas

Best cephalosporins to protected Blood-brain, prostate, bronchi, ocular barriers

This is the most common reason you would reach for these unless specific C&S states otherwise

49
Q

Third Generation Cephalosporin:

Ceftazidime:

Uncommon use

A

Injection only

Similar to cefotaxime/ceftriaxone, except additional activity against Pseudomonas

50
Q

Carbapenems

A

Parent drug originally isolated from Streptomyces cattleya

Modified to the drugs currently in use

51
Q

Carbapenems:

Spectrum

A

Gram positive, gram negative, aerobic and anaerobic

Activity against some extended spectrum beta lactamases ans Pseudomonas

52
Q

Carbapenems:

Use

A

parenteral use only,

Poor penetration into protected tissue

Reserved for resistant infections, and should only be used in consultation with a clinical pharmacologist or infectious disease expert

53
Q

Carbapenems:

Meropenem

A

most commonly used

IV, IM, SQ

54
Q

Carbapenems:

Imipenem / cilastatin

A

cilastatin added to decrease renal metabolism of imipenem and maintain antimicrobial activity of imipenem in the urine

Less commonly used, need larger volumes, less stable

General Pharmacology 2 (17 decks)

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