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PHARMACOLOGY 3 > 9 – Macrolides > Flashcards

9 – Macrolides Flashcards

1
Q

Think of macrolides in groups:

A
  • Tylosin
  • “respiratory disease
  • Azithromycin (human formulation): small animals
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2
Q

Tylosin

A
  • Used in large animal production and a bit in small animal
  • Feed premix, medicated water or infectable
  • Variety of label claims
  • *compounded forms used for small animal GI conditions
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3
Q

What are some label claims of Tylosin?

A
  • Swine dysentery and porcine liver enteropathy
  • Reduction in liver abscesses in feedlot cattle
  • Aid in treatment of respiratory disease and necrotic enteritis in broiler chickens
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4
Q

What are some respiratory disease macrolides for vet use?

A
  • Tilmicosin
  • Tulathromycin
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5
Q

Tilmicosin (Micotil)

A
  • For SC use ONLY in cattle and sheep
  • -oral premix and liquid for swine, feedlot cattle and rabbits
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6
Q

Tulathromycin (Draxxin)

A
  • SC in cattle
  • IM in swine
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7
Q

Azithromycin (Zithromax)

A
  • Human formulation widely used in vet med small animal practice
  • Variety of oral tablet and suspension formulation
  • Commonly used EXTRA-LABEL in small animal practice
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8
Q

Lincosamides

A
  • Different structure, but similar to macrolides
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9
Q

What is an important lincosamide in vet med?

A
  • Clindamycin
  • (Lincomycin: widespread resistance, not used as much anymore)
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10
Q

Clindamycin (Antirobe/Clinacin oral capsules or solution)

A
  • Increased antimicrobial activity compared to Lincomycin
  • Commonly used for skin, dental, bone or anaerobic infections
    o Used for protozoal diseases
  • Resistance emerges rapidly
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11
Q

Pleuromutilins: Tiamulin

A
  • Denagard liquid solution or feed premix
  • Brachyspira hydodysenteriae to prevent and treat swine dysentery
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12
Q

Streptogramins: Virginiamycin

A
  • Stafac, V-max feed premix
  • Feedlot cattle
  • Swine
  • *poultry: prevent necrotic enteritis caused by C. perfringens
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13
Q

Macrolides and lincosamides mechanism of action

A
  • Binds to bacterial ribosomal 50S sub-unit
    o Not same spot as phenicols, but same effect
    o Causes incorrect tRNA translation
    o Disrupts bacterial protein synthesis
  • *activity may be pH-dependent
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14
Q

ML and lincosamides may be pH-dependent

A
  • Basic amine groups are ionized in acidic pH, with DECREASED entry into bacterial cell
  • *still clinically effective though due to high DRUG CONCENTRAION
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15
Q

ML and lincosamides: usually time-dependent

A
  • But azithromycin shows some CONCENTRATION-dependent effects too
  • *can administer relatively infrequently
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16
Q

ML and lincosamides: spectrum of activity, generally effective

A
  • Most gram +
  • Some gram –
  • Some anaerobes
  • Helicobacter
  • Some mycoplasma (in vitro, but not really in the real world)
  • Intracellular pathogens (Lawsonia and Rhodococcus)
  • Others: Spirochetes, Chlamydia, Toxoplasma/Neospora)
17
Q

ML and lincosamides: spectrum of activity, NOT/LESS effective

A
  • Most gram negative enterics
  • Pseudomonas
  • Enterococcus
  • *resistance emerges rapidly in many bacterial species: cross-resistance is common
18
Q

What are some mechanisms of resistance?

A
  • Inability to bind to bacterial ribosome
    o rRNA methylation (erm gene)
    o mutations to ribosomal binding sites (uncommon)
  • efflux pumps/decreased entry
  • enzymatic inactivation of drugs
  • plasmid mediated resistance genes: cross resistance
19
Q

Plasmid mediated resistance genes

A
  • resistance develops and transfers quickly
  • *cross resistance to multiple ML/lincosamides is common
  • But differences between 14, 15, 16 member ring cross-resistance
20
Q

Feedlots and antimicrobial use

A
  • Probably now more macrolides than tetracyclines used now
    o Especially tulathromycin
21
Q

Absorption of macrolides and lincosamides

A
  • Lots of variation in oral F between them
    o Azithromycin and clindamycin=well absorbed
    o Some need special coating (ex. erythromycin)
  • *food may alter absorption (read the label)
22
Q

Distribution of macrolides and lincosamides

A
  • Generally highly lipophilic
    o Low plasma concentrations
    o **Very high Vd
  • Very high ‘lung’ concentrations
  • CSF: lincomycin and clindamycin have increased distribution
  • Accumulates in leukocytes
23
Q

Macrolides and lincosamides: accumulates in leukocytes

A
  • Effective against (some) intracellular pathogens
  • Delivered to site of infection
24
Q

Elimination of macrolides and lincosamides

A
  • Varies depending on drug
  • Typically hepatic metabolism
  • Excretion via bile or urine
25
Q

Some macrolides have very long half-lifes: examples and info

A
  • Tilmicosin, tulathromycin, gamithromycin, tildopirosin
  • Once distributed into tissue, it is SLOWLY elimininated from the body
    o Re-distribution back to plasma before elimination
    o ‘different’ plasma and tissue half-lives
  • *long withdrawal periods, but not prohibitive
    o Concentrations not that high in edible tissues
26
Q

Draxxin administration via pneumatic dart gun

A
  • Big difference in drug exposure compared to if you administered it normally
  • Not all the animals that ‘got darted’ had successful injections
  • More damage when darted
27
Q

**What is the adverse event of Tilmicosin?

A
  • Cardiovascular toxicity
    o Not an issue if used according to label SC ose in cattle and sheep
    o Fatal when injected IV
  • Might be fatal if administered parenterally in humans, goats, dogs
    o *Calcium channel blockage/depletion
    o Tachycardia, but negative inotrope (poor contractility)
    o IV Ca 2+ may be protective
28
Q

What are some other adverse events of macrolides and lincosamides?

A
  • GI toxicity after oral administration
    o Vomit/diarrhea=common
    o GI flora changes (clostridial overgrowth)
  • Injection site reactions
  • Hyperthermia
  • Generally minimal drug interactions
29
Q

AE: vomit/diarrhea

A
  • Especially oral erythromycin
  • Maybe some GI irritation or altered motility?
30
Q

AE: GI flora changes (clostridial overgrowth)

A
  • Fatal colitis reported in horses after erythromycin use
  • *caution when using lincosamides (clindamycin)in rodents/lagomorphs (hindgut)
    o But macrolides are OK (ex. oral tilmicosin approved for meat rabbits)
31
Q

AE: injection site reaction

A
  • Most have some degree
  • Very irritating
    o Tilmicosin (must go SC)
    o Erythromycin IM injections
32
Q

AE: hyperthermia

A
  • Reported after erythromycin injections in foals
33
Q

Drug interactions

A
  • Some are CYP inhibitors
    o Ex. erythromycin
  • Antagonism when used with phenicols
    o BOTH bind to parts of ribosomal 50S submit
    o Macrolides do NOT cause bone marrow toxicity
34
Q

What are some non-antimicrobial properties of macrolides?

A
  • Erythromycin: GI prokinetic (motilin receptor receptor)
  • Anti-inflammatory and immunomodulation
    o Inhibit production of many pro-inflammatory cytokines
    o Decrease neutrophil migration
    o Ex. Tylosin commonly used as GI anti-inflammatory

PHARMACOLOGY 3 (15 decks)

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