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Pharm Test 3 > Antimicrobials 2 > Flashcards

Antimicrobials 2 Flashcards

1
Q

definining molecular structure of the ‘penicillins’

A

beta lactam ring
* Confers activity B
* Destroyed by enzymes secreted by some bacteria: “penicillinases” or “beta-lactamases”
* Temperature labile; warming or freezing can destroy the BL ring

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2
Q

penicillins are only effective against what kind of bacteria?

A

growing

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3
Q

mechanism of action of penicillins?

A

inhibit cell wall synthesis
Beta lactams covalently bind to & inactivate the transpeptidase enzyme
Defective cell wall > as cells divide, they lyse & die

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4
Q

what kind of bacteria do penicillins work best against and why?

A

Penicillins tend to work best against Gram-positive bacteria, which have a thick, unprotected peptidoglycan layer

In Gram-negative bacteria:
* Binding sites are different on transpeptidases
* External bilayer can be difficult to penetrate
* Some bacteria secrete penicillinases into the periplasm

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5
Q

penicillins pharmacokinetics

A
  • Distribute well to extracellular fluids everywhere except CNS & prostate (unless inflamed), poor penetration into cells > low Vd
  • Acid stability varies; some cannot be given orally due to acid hydrolysis
  • Short half-lives (≤ 2 h)
  • Elimination: No metabolism; renal excretion of unaltered drug
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6
Q

Main Adverse Effects of penicillins

A

1) Hypersensitivity
* Mild allergy to anaphylactic reaction

2) Colitis in hindgut fermenters
* Oral penicillins can disturb gut flora

3) Breakthrough seizures in epileptics
* Beta-lactams inhibit GABAa receptors in the brain > increases neuronal excitability

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7
Q

penicillins resistance profile and reasons

A

Fairly common

  1. Poor penetration of complex Gram-neg. cell wall
  2. Acquired bacterial penicillinases
    - Plasmid-encoded > can be transferred to other bacteria
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8
Q

Penicillin G: spectrum, excellent against what type of bacteria, half-life, administration strategies, stability

A

Narrow spectrum Excellent against:
* Gram-positive aerobes
* Anaerobes

  • Sodium salt has 30 min half-life > admin. frequently, or use a depot formulation
  • Depot formulation consists of penicillin bound to a molecule such as procaine or benzathine > penicillin gradually dissociates from procaine at IM or SC injection site > longer duration of action
  • Penicillin G is not acid stable, must be administered parenterally
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9
Q

amoxicillin: spectrum, what bacteria it is effective against

A

Example of an extended spectrum penicillin

  • Gram-pos. aerobes, anaerobes, plus a variety of Gram-neg. aerobes, especially Enterobacteriaceae
  • Activity against Gram-pos. aerobes & anaerobes is generally less than that of penicillin G
  • Oral bioavailability exceeds 90%
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10
Q

what is ampicillin and its uses?

A

similar drug to amoxicillin but mainly used parenterally because of poorer oral bioavailability
>but this means more remains in GI tract > GI upset more likley

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11
Q

what is potentiated penicillin

A

Bacterial penicillinases can be inactivated with penicillinase inhibitors such as clavulanic acid
> called a “potentiated penicillin”

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12
Q

Penicillins Flash Card: mechanism of action

A

Inhibition of cell wall synthesis

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13
Q

Penicillins Flash Card: Main adverse effects

A
  • Hypersensitivity
  • Contact dermatitis risk > not used topically
  • Potentially fatal colitis in hindgut fermenters (oral admin.)
  • Reduction of seizure threshold
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14
Q

Penicillins Flash Card: general spectrum

A
  • Penicillin G: Gram-pos. aerobes, anaerobes
  • Amoxicillin: Same as pen G, plus several Gram-neg. aerobes
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15
Q

Penicillins Flash Card: Health Canada prudent use stats

A

First line: Penicillin G, amoxicillin Second line: Potentiated penicillins

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16
Q

Penicillins Flash Card: PK features

A

Excreted intact in the urine
Penicillin G is not acid-stable
Oral bioavailability of amoxicillin is ~90%

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17
Q

what drug class are the cephalosporins similar to? in what ways?

A

Similar to penicillins:
* Mech. of action
* Distribution
* Elimination
* Main adverse effects

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18
Q

what route of administration is not good for cephalosporins and why?

A
  • Most are not acid stable > cannot be given orally
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19
Q

if an animal has a penicillin allergy will cephalosporins be safe?

A

About 5% of humans with a penicillin allergy are also allergic to cephalosporins > avoid in an animal with a penicillin allergy to be safe

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20
Q

3rd gen cephalosporins enter what hard to reach tissue reasonably well?

A

CNS

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21
Q

1st gen cephalosporins spectrum of activity

A

1st generation: Similar to amoxicillin
>Mainly Gram-pos. aerobes, + anaerobes, plus some medically important Gram-neg. aerobes

22
Q

3rd gen cephalosporins spectrum of activity

A
  • Less activity against Gram-pos. & anaerobic bacteria but better against Gram-neg. aerobes
23
Q

cephalexin is what type of drug? usaed mainly in what animals?

A

1st gen cephalosporin, used mainly in small animals

24
Q

ceftiofur is what type of antibiotic? mainly used for what?

A

3rd gen cephalosporin

resp. infections in livestock & horses; foot rot & metritis in cattle; UTI in dogs, etc.

25
Q

Cefovecin is what type of drug? what is a drawback?

A

3rd gen cephalosporin
o 2-week formulation essentially guarantees inappropriate duration of therapy in most patients
>veterinary surgeons prescribing cefovecin rarely justified its use

26
Q

Cephalosporins Flash Card: mechanism of action

A

Inhibition of cell wall synthesis

27
Q

Cephalosporins Flash Card: main adverse effects

A
  • Hypersensitivity
  • Potentially fatal colitis in hindgut fermenters (oral admin.)
  • Reduction of seizure threshold
28
Q

Cephalosporins flash card: general spectrum

A
  • First gen.: Similar to amoxicillin
  • Third gen.: A mix, but mainly Gram-neg. aerobes
29
Q

Cephalosporins flash card: health canada prudent use stats

A

First line: First generation
Second line: Third generation

30
Q

cephalosporins flash card: PK features

A

Only a few are acid-stable (e.g., cephalexin)
Not destroyed by penicillinases, but may be inactivated by some “beta-lactamases”
Some third-gen drugs enter CNS readily

31
Q

what are the major types of beta-lactams? scope of effect?

A

Penicillins
-penicillin G: Gram positive aerobes, anaerobes
-amoxicillin: Gram positive aerobes, anaerobes, some gram negative aeroboes

Cephalosporins
-1st gen: Gram positive aerobes, anaerobes, some gram negative aeroboes
-3rd gen: gram negative aerobes, some grame pos aerobes, some anaerobes

32
Q

two main uses for aminoglycosides

A

1) Systemic for severe Gram-neg. aerobic infections
2) Topical (e.g., for Staph)

33
Q

do aminoglycosides cross cell membranes well? why?

A

limited ability to cross membranes > highly ionized

34
Q

best route of administration for aminoglycosides

A

must be given parenterally for systemic treatment

-oral absorption only ~3%

35
Q

most used drug in the aminoglycosides group

A

gentamicin

36
Q

aminoglycosides mechanism of action

A

Inhibit bacterial protein synthesis by binding to bacterial ribosomes

AGs cause wrong AA to be incorporated into growing protein
> these can form lethal porins
> kill bacterial cell

37
Q

spectrum of activity for aminoglycosides

A

Gram-neg. aerobes
+ Staph (including MRSA/MRSP)
+ Mycoplasma

38
Q

resistance considerations for aminoglycosides:

A

1) Constitutive: Entry of drug into cell requires oxygen-dependent transport system
> AGs are therefore ineffective against anaerobes

2) Plasmid-acquired: Aminoglycosidase

39
Q

mechanism of aminoglycosides nephrotoxicity?

A

1) NEPHROTOXICITY

  • AGs are eliminated by filtration into the urine intact
  • AGs enhance free-radical formation following accumulation in renal tubular cells > damage some renal tubular epithelial cells in every patient
  • Proximal renal tubular epithelium regenerates well > usually not a problem (i.e., as long as cell loss is not extensive)
  • Ordinary dose can be very damaging to kidneys of dehydrated patients & patients with renal disease (T1/2 of most AGs doubles in old age)
  • Excretion is directly proportional to creatinine clearance > helps in making dosage adjustments
40
Q

what types of patients have an increased risk of adverse effects from aminoglycosides?

A

dehydrated and those with renal disease

41
Q

how can we minimize nephrotoxic adverse effects of aminoglycosides?

A

AGs enter renal tubular cells via a saturable transporter
> amount entering cells depends on duration of exposure rather than peak concentration

Damage is minimized by allowing a washout period each day
> give single daily dose and allow concentrations to fall for remainder of day

42
Q

use and considerations for aminoglycosides in food animals

A

IM use in cattle may result in drug residues detectable for >1 year (e.g., kidney)

Approved only for neonatal colibacillosis in piglets, and for intrauterine infusion (negligible absorption from sites of admin) in dairy and beef cattle and horses (also used in newborn chicks)

43
Q

use and considerations for aminoglycosides in food animals

A

IM use in cattle may result in drug residues detectable for >1 year (e.g., kidney)

Approved only for neonatal colibacillosis in piglets, and for intrauterine infusion (negligible absorption from sites of admin) in dairy and beef cattle and horses (also used in newborn chicks)

44
Q

ototoxicity of aminoglycosides mechanism? how to avoid?

A

AGs damage CN VIII & hair cells in cochlea & vestibular apparatus

  • Can cause permanent, severe, high-frequency hearing loss
  • Topical otic prep: ensure tympanum is intact
45
Q

3 main aminoglycosides and their uses:

A

Gentamicin:
- Broadest spectrum (Gram-neg. aerobes, Staph, mycoplasma)
- The most commonly used AG

Tobramycin:
* Used second-line for infections resistant to gentamicin

Amikacin
* Used second-line for infections resistant to gentamicin
* Resistant to many aminoglycosidases

46
Q

Aminoglycosides Flash Card: mechanism of action

A

Inhibition of protein synthesis (bactericidal effect)

47
Q

Aminoglycosides Flash Card: main adverse effects

A
  • Nephrotoxicity
  • Ototoxicity
48
Q

Aminoglycosides Flash Card: general spectrum

A
  • Gram-neg. aerobes
  • Staph
  • Mycoplasma
49
Q

Aminoglycosides Flash Card: health canada prudent use stats

A

First line: Topical admin.
Second line: Systemic admin.

50
Q

Aminoglycosides Flash Card: PK features

A
  • Highly ionized > negligible oral or topical absorption
  • Food residues > 1 year with parenteral administration

Pharm Test 3 (16 decks)

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