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PHARMACOLOGY 3 > 8c – Tetracyclines > Flashcards

8c – Tetracyclines Flashcards

1
Q

What are the NEED to know vet med tetracyclines?

A
  • Tetracycline (TC)
  • Oxytetracycline (OTC)
  • Chlortetracycline
  • *Doxycycline: ‘different one’
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2
Q

Tetracycline (TC): formulations

A
  • Licensed in food animals and horses
  • Water-soluble (oral) powders
  • Oral/intrauterine boluses
  • Some human oral capsules used extra label in dogs/cats
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3
Q

Oxytetracycline (OTC): formulations

A
  • Licensed in food animals ONLY
  • Oral: feed premix or water soluble powder
  • Intrauterine suspension
  • Injectable products: 2 differnet ones
  • Some human oral capsules used extra label in dogs/cats
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4
Q

*What are the 2 injectable products of oxytetracycline?

A
  • Short-acting: 100mg/mL “LP” formulations, for IM or IV use
  • Long-acting: 200-300mg/ml “LA” formulations, for IM or SC use
    o ‘nasty’ ingredients/carriers=for consistent pH, stability, sterility (can be irritating though!)
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5
Q

Onycin: tetracycline HCl powder

A
  • Yellow power
  • Wrap on wounds
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6
Q

Chloretetracycline: formulation

A
  • Oral premixes
  • Boluses for food animals
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7
Q

Doxycycline: formulations

A
  • Primarily in small animals (and horses)
  • Oral formulations: human tables or capsules used (100mg)
  • Vet formulations were available, but NOT anymore (dental gel)
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8
Q

Oral formulations of doxycycline: ‘smaller doses’ (from human med)

A
  • Smaller ‘modified release’ capsules may NOT be appropriate
    o Intended for non-antimicrobial purposes
    o Wont be released until it is too late
  • May need compounded forms to get appropriate size for small patients
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9
Q

What are the tetracyclines mechanism of action?

A
  • Binds to bacterial ribosomal 30S sub-unit
    o Cause incorrect tRNA translation
    o Disrupts bacterial protein synthesis
  • *requires energy-dependent transport into bacterial cell to reach binding sites (by the bacteria)
    o Animals lack tetracycline transporters=safe in mammalian species (no protein inhibition)
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10
Q

TCs have multiple charges on functional groups: what are they at physiological pH?

A
  • Mostly zwitterion form
    o Both + and – but overall=NEUTRLAL
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11
Q

TC are TIME-dependent antimicrobials

A
  • *Try for prolonged exposure, not high peak concentration
  • *only ones that are concentration dependent=aminoglycosides so far)
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12
Q

Antimicrobial activity and potency of tetracyclines

A
  • All basically the same
  • *differences in clinical efficacy due to PK (likely NOT big)
    o Maybe something with absorption
    o Doxycycline may have increased permeability and activity
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13
Q

What are tetracyclines potentially effective for?

A
  • Some gram + and –
    o Respiratory disease in food animals
  • Many anaerobes
  • Some Mycoplasma: DON”T believe it is suceptible
  • ***FANTASTIC:
    o Tick-borne bacteria, Chlamydia (phenicols first), protozoa, spirochetes
    o Ex. Potomac horse fever (Neoricketssia), Rocky Mountain spotted fever (Rickettsia)
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14
Q

What are tetracyclines potentially NOT/LESS effective?

A
  • Lots of resistance
  • Staphylococci often resistant
  • Gram – enterics
  • Pseudomonas
  • Enterococcus
  • *resistance emerges rapidly in many bacterial species
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15
Q

Susceptibility testing

A
  • Good idea
  • Could work, but likely to be resistant!
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16
Q

What are some mechanisms of resistance to tetracyclines?

A
  • Plasmid-mediated tet resistance genes=widespread and FAST!
    o Significant to impact clinical usefulness
  • Decreased tetracycline in bacterial cell
    o Failure of active transport into bacterial cell
    o Increased efflux from the cell
  • Enzymatic inactivation of tetracycline
  • Production of proteins that protect bacterial ribosome
17
Q

Tetracycline absorption PK

A
  • CTC/OTC: poor oral bioavailability
  • Doxycycline: much higher oral bioavailability
    o Varies with feed status and formulation
  • INJECTABLE: high bioavailability
    o LA formulation=flip-flop kinetics (SLOW absorption, drives rate of elimination)
18
Q

Tetracycline oral bioavailability in pigs example

A
  • *Tetra and CTC=higher oral bioavailability in fasted state
  • variance becomes important when LOW bioavailability (ex. if 80+% bioavailability variance is NOT a big deal)
19
Q

What is the impact of variance in for low bioavailability drugs? (ex. bioavailability %=3 +/- 3)

A
  • Spread from 0-6=big difference!
  • *variance is magnified
    o 6% already is not good, but better than 1%
20
Q

Tetracycline distribution PK

A
  • Good distribution to most tissues and fluids (better than beta-lactams, aminoglycosides and sulfas)
    o Vd=1L/kg in most species
    o EXCEPTION: doesn’t penetrate CSF well
  • Low/moderate protein binding
    o EXCEPTION: DXC (~90%)
  • **bind to Ca/Mg (divalent cations)
21
Q

If TCs binds to Ca/Mg, which tissues might be affected?

A
  • BONE (+ teeth in kids)
  • NOT a food safety risk as not really consuming bones
    o Doesn’t look great when things glow under black light
22
Q

Tetracycline elimination PK

A
  • Metabolism: very LITTLE
  • Small amounts excreted via
    o Feces: biliary+P-gp (some enterohepatic circulation can occur)
    o **more important for doxycycline
  • Uncharged TC mainly excreted by kidneys=high concentrations in urine (useful for UTI)
    o Longer T half life with renal failure (but dose modification NOT necessary)
    o May still be useful even if susceptibility report says R
    o Exception: doxycycline=more in feces
23
Q

Tetracyclines half life elimination

A
  • 6-8hrs
    o Don’t need to dose a bunch of times a day (even though time-dependent)
  • Except long acting: 24hrs
24
Q

Tetracycline AE

A
  • Generally safe
  • Nephrotoxicity=unlikely (higher dose and dehydration=risk factor)
  • CV collapse with rapid IV injection (ex. short acting): dilute and inject slowly
    o Long acting=NOT given IV (only IM/SC)
  • Chelation by calcium and heavy metals
  • Gi: vomit/diarrhea
  • Injection site reaction: depends on drug carrier
25
Q

Chelation by calcium and heavy metals: tetracycline AE

A
  • Recommended to NOT administer oral tetracyclines with dairy products=decrease ORAL bioavailability
  • Administration in young animals=teeth staining (but not a big deal)
26
Q

What is a non-antimicrobial use of tetracyclines?

A
  • Can RELAX flexor tendons
    o High dose IV given to neonatal foals with angular limb deformity
    o Mechanism: maybe inhibits matric metalloproteinase enzymes
  • Mild anti-inflammatory effects

PHARMACOLOGY 3 (15 decks)

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