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Pharm Test 3 > Antimicrobials 3 > Flashcards

Antimicrobials 3 Flashcards

1
Q

tetracyclines mainly used to treat infections with what type of bacteria?

A

Used mainly to treat infections caused by atypical bacteria in all species

Also effective for many common bacterial infections of livestock

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2
Q

tetracyclines mechanism of action

A
  • Bind to bacterial ribosomes
    > inhibit protein synthesis
  • Bacteriostatic
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3
Q

tetracyclines spectrum of activity?

A

Small animals:
1st choice for atypicals

Livestock:
Effective against many/some common G+ & G- aerobic & anaerobic pathogens, as well as atypical bacteria

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4
Q

pharmacokinetics of tetracyclines: absorption

A

Absorption:
* Oral bioavailability varies with drug & species but tends to be low
* Doxycycline has better oral bioavailability than most other
tetracyclines
* Divalent cations in food (e.g., calcium in milk, cheese) can markedly inhibit oral absorption

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5
Q

pharmacokinetics of tetracyclines: distribution

A
  • Most distribute well to the extracellular fluid compartment, except the CNS
  • Distribution into cells depends on lipid solubility; doxycycline is the most lipid sol.
    > enters host cells well, including prostate & CNS

Tetracyclines bind to multivalent cations such as calcium, and become incorporated into growing bone and teeth
>A food animal residue concern

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6
Q

Pharmacokinetics of tetracycline – Distribution

A

Tetracyclines bind to multivalent cations such as calcium, and become incorporated into growing bone and teeth
>A food animal residue concern

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7
Q

Pharmacokinetics of tetracycline – Elimination

A

Most tetracyclines are excreted primarily by glomerular filtration into the urine

Biliary & non-biliary excretion into the intestinal lumen also occurs to an extent depending on lipid solubility of drug
> mainly doxycycline, which is much more lipid soluble than most other tetracyclines and is eliminated almost entirely through the intestinal tract into feces

Enterohepatic recycling can extend drug elimination half life

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8
Q

Pharmacokinetics of tetracycline – Elimination

A

Most tetracyclines are excreted primarily by glomerular filtration into the urine

Biliary & non-biliary excretion into the intestinal lumen also occurs to an extent depending on lipid solubility of drug
> mainly doxycycline, which is much more lipid soluble than most other tetracyclines and is eliminated almost entirely through the intestinal tract into feces

Enterohepatic recycling can extend drug elimination half life

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9
Q

tetracycline resistance profile and machanisms for resistance

A

Resistance is widespread

Two main acquired (i.e., plasmid-encoded) mechanisms:
1. Efflux pump
* Removes drug from bacterial cell
* Efflux pump may be overwhelmed by high drug concentration
> explains improved efficacy with topical application in some situations
2. Ribosomal protection protein
- inhibits binding of tetracycline

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10
Q

Adverse effects of tetracyclines:

A

1) Incorporation into growing teeth & bones
>Discoloration of growing teeth

2) Renal tubular damage
>Use of expired (outdated) drug; administration to dehydrated patients (may be fatal); administration of high dosages

3) Tissue irritation

4) Esophageal lesions from doxycycline in cats
>Broken tablets or undissolved capsules can cause significant esophageal lesions & strictures in cats

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11
Q

Adverse effects of tetracyclines:

A

1) Incorporation into growing teeth & bones
>Discoloration of growing teeth

2) Renal tubular damage
>Use of expired (outdated) drug; administration to dehydrated patients (may be fatal); administration of high dosages

3) Tissue irritation

4) Esophageal lesions from doxycycline in cats
>Broken tablets or undissolved capsules can cause significant esophageal lesions & strictures in cats

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12
Q

Tetracyclines Flash Card: mechanism of action

A

Inhibition of protein synthesis (bacteriostatic effect)

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13
Q

Tetracyclines Flash Card: main adverse effects

A
  • Incorporation into growing teeth & long bones
  • Nephrotoxicity in dehydrated patients
  • Tissue irritation (pain on injection; vomiting oral dose)
  • Risk of esophageal damage in cats
  • Etc.
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14
Q

Tetracyclines Flash Card: general spectrum

A
  • All species: Atypical bacteria (usually drug of choice)
  • Livestock: Broad Spectrum
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15
Q

Tetracyclines Flash Card: health canada prudent use stats

A

first line

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16
Q

Tetracyclines Flash Card: PK features

A

Lipid-soluble tetracyclines (e.g., doxycycline) are useful against intracellular pathogens

17
Q

are sulfonamides very effective alone? why?

A

Resistance to sulfonamides is now widespread among pathogens of small animals and humans
> largely ineffective when used alone

18
Q

What are Potentiated sulfonamides? when are they used?

A
  • Effectiveness of the sulfonamide (S) is restored when combined with ‘diaminopyrimidine inhibitors’ such as trimethoprim (TM)
  • TMS combinations are widely used in large animal medicine
  • Important off-label option for exotic animals
19
Q

sulfonamides mechanism of action

A

Folic acid (vitamin B9) is required for DNA, RNA, & protein synthesis
* Mammals acquire all they need from the diet
* Bacteria must synthesize it from PABA

Sulfonamides and trimethoprim inhibit different steps in the bacterial folic acid synthesis pathway:

Sulfonamides
>Resemble PABA
>Competitively inhibit dihydropteroate synthetase

Trimethoprim
>competitively inhibits dihydrofolate reductase

Note: Pus contains huge amounts of PABA, so sulfonamides are ineffective in the presence of pus

20
Q

sulfonamides spectrum of activity

A

Small animals: atypical bacteria
Livestock: atypical bacteria, and some broad spectrum effect besides (Effective against many common G+ & G- aerobic & anaerobic pathogens)

Extremely broad spectrum when first marketed (all
bacteria, even some protozoa), but rapid selection for resistance occurred within the first decade of use

Used clinically like tetracyclines:
* Small animals
>Most pathogens are resistant except atypical bacteria, many of which are sensitive

  • Livestock
    A variety of common pathogens are sensitive
    > important 1st-line option
  • Also used increasingly in humans & small animals for sporadic bacterial cystitis where high concentration of drug in urine overwhelms resistance mechanisms
  • Used for bacterial prostatitis due to distribution
21
Q

pharmacokinetics of sulfonamides

A

Absorption & Distribution:
* Good oral absorption
* Distribute well to all tissues
* Tissue debris & pus provide PABA > substrate out-competes sulfonamide > reduced efficacy of this class of drugs in presence of pus

Elimination:
* A combination of renal excretion and hepatic metabolism
* Metabolites can accumulate in renal tubules
> renal damage; can be severe in dehydrated patients

22
Q

sulfonamide resistance profile and mechanisms

A
  • Common among small animal & human pathogens
  • Relatively uncommon among livestock pathogens

Bacteria can acquire a plasmid-encoded version of dihydropteroate synthetase that binds PABA better than sulfonamides

Bacteria can also acquire a plasmid-encoded dihydrofolate reductase that does not bind trimethoprim well

The likelihood of a bacterium acquiring modified versions of both enzymes is lower, which is why potentiated sulfonamides are so much more effective than either a sulfa or TM alone

23
Q

sulfonamides adverse effects

A

Usually due to the sulfonamide rather than TM

  • More allergenic than most drugs (contact dermatitis > not used topically)
  • KCS (keratoconjunctivitis sicca or “dry eye”) in dogs
    -Sulfas are “lacrimotoxic” in dogs
  • Nephrotoxicity: precipitation in renal tubules in dehydrated patients > can cause renal failure
24
Q

TMS Flash Card: mechanism of action

A

Inhibition of folic acid synthesis

25
Q

TMS Flash Card: main adverse effects

A
  • Lacrimotoxicity in dogs (KCS)
  • Nephrotoxicity in dehydrated patients
  • Hypersensitivity (including contact dermatitis)
26
Q

TMS flash card: general spectrum

A
  • All species: Atypical bacteria, UTIs
  • Livestock: Fairly broad spectrum
27
Q

TMS flash card: health canada prudent use stats

A

First-line

28
Q

TMS flash card: PK features

A

Ineffective in presence of pus
Distribute to all tissues

Pharm Test 3 (16 decks)

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