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Pharmacology Final > Macrolides/Lincosamides and Sulfonamides > Flashcards

Macrolides/Lincosamides and Sulfonamides Flashcards

1
Q

macrolides MOA

A

protein synthesis inhibitor- irreversible binding to 50 S ribosome prevents protein synthesis

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2
Q

are macrolides bacteriostatic or bactericidal

A

generally bacteriostatic but can be -cidal at high concentrations

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3
Q

what characteristic do some macrolides possess that can be useful to treat certain difficult infections?

A

anti-biofilm activity: useful for infx that are hard to treat bc of biofilm formation

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4
Q

what other effects do macrolides have?

A

immunomodulatory effects independent of abx activity
inhibit infiltration of neutrophils into airway, inhibit production of pro-inflammatory cytokines

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5
Q

what effect do macrolides have on the GI tract in horses, dogs and cattle?

A

pro-kinetic: act as direct motilin receptor agonists

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6
Q

macrolides spectrum of activity

A

generally considered broad-spectrum
good activity against gram + aerobes, gram - aerobes, and some anaerobic bacteria

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7
Q

what bacteria are resistant to macrolides?

A

Enterobacteriaceae, Psuedomonas, Nocardia, Mycoplasma, Chlamydia, Mycobacterium

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8
Q

what is the representative drug for macrolides

A

erythromycin
new ones are azithrymycin, clarithromycin

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9
Q

what are the mechanisms of resistance against macrolides?

A
  1. rRNA methylation: prevents binding of drug to ribosome
  2. active drug efflux
  3. enzymatic inactivation (less common)
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10
Q

how are macrolides absorbed?

A

variable absorbed from GI tract if not inactivated by gastric acid. oral formulas are often enteric-coated

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11
Q

how are macrolides administered?

A

IV or IM administration leads to rapid absorption, but pain and swelling occurs at injection sites :(

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12
Q

where are macrolides distributed?

A

widely distributed in tissues EXCEPT those of CNS

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13
Q

where are macrolides NOT distributed to?

A

CNS!

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14
Q

metabolism and excretion of macrolides is ______ dependent

A

drug dependent: some undergo hepatic metabolism and biliary excretion (erythromycin, tiamulin), others are excreted unchanged in bile and urine (tylosin, tilmicosin)

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15
Q

what macrolides inhibit cytochrome P450 enzymes?

A

erythromycin and tiamulin

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16
Q

adverse effects of macrolides

A
  • incidence is relatively low
  • all are irritants and cause severe pain with IM inj
  • dose-related GI disturbances in most animals
  • GI effects can be life-threatening in horses!
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17
Q

how can macrolides lead to death in horses?

A

erythromycin in horses can lead to Clostridium overgrowth, leading to serious D+ illness/death

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18
Q

what macrolide can produce cardiac toxicity in species other than cattle and swine?

A

tilmicosin
- fatal after IV inj in humans
- calcium channel blockade

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19
Q

drug of choice for Campylobacter D+ or abortion

A

erythromycin

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20
Q

what is erythromycin often used for?

A
  • drug of choice for Campy D+ or abortion
  • penicillin-alternative in pen sensitive animals
  • less effective alternative to clindamycin or metronidazole in anaerobic infx
  • ampicillin or amoxicillin alternative in txt of lepto
  • tetracycline alternative for rickettsial infx
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21
Q

what is tylosin used for

A

local and systemic infx caused by mycoplasmas, Gm+, anaerobes and some respiratory Gm- pathogens

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22
Q

what is tilmicosin used for

A

used only in cattle injectably and swine medicated feed for respiratory disease

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23
Q

what is tiamulin used for

A

used in swine for control and txt of swine dysentery (Brachyspira hyodysenteriae) and mycoplasmal arthritis

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24
Q

what is clarithromycin used for

A

drug of choice for treating Rhodococcus equi when combined with Rifampin

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25
Q

what is the drug of choice for treating Rhodococcus equi?

A

Clarithromycin + Rifampin

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26
Q

what is Tulathromycin?

A

Draxxin!!

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27
Q

what type of drug is Draxxin

A

macrolide

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28
Q

what is tulathromycin (draxxin) used for

A

long-acting, single-dose macrolide for respiratory disease in cattle and swine. drug accumulates in lung tissue

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29
Q

lincosamides

A

from Lincoln, NE!
- clindamycin, lincomycin, pirlimycin

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30
Q

are macrolides bacteriostatic or bactericidal?

A

can be either depending on drug concentration, bacterial species, and inoculum/amount of bacteria

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31
Q

lincosamides MOA

A

inhibition of protein synthesis: binds to the 50S ribosomal subunit (same site as macrolides) and inhibits peptidyl transferase

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32
Q

what do lincosamides have activity against

A

Gram + aerobes, mycoplasma, and anaerobes

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33
Q

distribution of lincosamides

A

widely distributed, excellent penetration of bone and soft tissues, including tendon sheaths. CNS levels are low
extensive metabolism in liver

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34
Q

how are lincosamides excreted?

A

excreted in urine, bile, and feces

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35
Q

what species are lincosamides contraindicated in? why?

A

horses, rabbits, hamsters and guinea pigs
- may produce severe, often fatal necrotizing enterocolitis (clostridial overgrowth)
- oral administration to ruminants can be fatal

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36
Q

what toxicities can occur with lincosamides?

A
  • necrotizing enterocolitis!
  • salmonellosis in dogs
  • neuromuscular blockage at high doses or when administered with anesthetics
37
Q

what drugs cause necrotizing enterocolitis in horses, rabbits, hamsters and guinea pigs?

A

lincosamides

38
Q

what is clindamycin used for?

A

dogs and cats for periodontal disease, osteomyelitis, dermatitis, and deep soft tissue infections
also used for toxoplasmosis in dogs and cats

39
Q

what is lincomycin used for?

A

used in swine for swine dysentery, staph, strep, and mycoplasma infx

40
Q

what is pirlimycin used for?

A

udder infusion for the txt of bovine mastitis caused by gram + cocci

41
Q

sulfonamides, diaminopyrimidines and their combos

A

Sulfonamides are derivatives of sulfanilamide and the substitutions on the molecule account for differences in potency, spectrum of activity and some PK properties.

42
Q

MOA of sulfonamides

A

interfere with synthesis of folic acid
inhibits formation of pteroic acid thru inhibition of dihydropterate synthase (DHPS) by acting as a false substrate/competitive inhibitor

43
Q

what are sulfonamides competing with for the enzyme dihydropteroate synthetase?

A

PABA: para-aminobenzoic acid

44
Q

how can action of sulfonamides be reversed?

A

excess of PABA; because they are competing and can overcome sulfa activity
tissue exudates and necrotic tissue should be removed before treatment with sulfas

45
Q

are sulfonamides bacteriostatic or bactericidal?

A

bacteriostatic

46
Q

sulfonamide activity is against

A

broad spectrum, inhibits growth of bacteria and protoza like toxoplasma and coccidia

47
Q

why aren’t sulfonamides good as single agents?

A

there has been extensive resistance that has developed :(

48
Q

why are sulfonamides selective to killing microorganisms?

A

animal cells take up pre-formed folic acid and thus don’t need to synthesize dihydrofolate/folic acid. folic acid is required for purine biosynthesis

49
Q

what bacteria are sulfonamides good against?

A

Bacillus spp, Brucella spp, Listeria, Nocardia, pyogenic Streptococcus spp, Cryptosporidium spp, Chlamidia and Chlamydophila spp, Pneumocystis, Coccidia remain susceptible.

50
Q

what bacteria are resistant to sulfonamides?

A

Mycobacterium spp, Mycoplasma spp, Psuedomonas.

51
Q

how have bacteria become so resistant to sulfonamides?

A

production of an insensitive dihydropteroate enzyme or hyperproduction of PABA, which antagonizes the sulfonamide
- there is complete cross-resistance for sulfonamides
- extensive resistance likely reflects the extensive use of these drugs over many years

52
Q

what are unique pharmacokinetic properties of sulfonamides?

A
  • widely distributes to tissues including CNS
  • very insoluble in water, can precipitate out and form crystals in acidic environments: urine!
  • combinations are used
53
Q

what drug can form crystals in acidic environments like urine?

A

sulfonamides

54
Q

how are sulfonamides metabolised?

A

primarily thru acetylation, with some glucoronidation and hydroxylation

55
Q

why are dogs less likely to get crystalluria from sulfonamides?

A

dogs are deficient in acetylatoin and don’t form the acetylated metabolites. the metabolites are less soluble in urine and increase risk of crystalluria
whereas glucoronide conjugates are highly water-soluble and rapidly excreted

56
Q

how are sulfonamides excreted?

A

urinary excretion via GFR, active tubular excretion and passive reabsorption

57
Q

what species is deficient in N-Acetylation, leading to less risk of toxicity from sulfonamides?

A

canines

58
Q

most common adverse effects of sulfonamides

A
  • urinary tract: crystalluria, hematuria, obstruction
  • hematopoetic disorders: thrombocytopenia, anemia
  • derm rxns: topic epidermal necrolysis
  • KCS: keratoconjuctivitis sicca
59
Q

what odd toxicity do sulfonamides have?

A

idiosyncratic drug rxns in animals and humans, 10 days to 3 weeks after exposure
hypersensitivity rxn or “drug fever”

60
Q

what drugs cause a hypersensitivity reaction or “drug fever” in dogs?

A

sulfonamides

61
Q

what breed has a severe reaction to sulfa drugs?

A

doberman pinschers- avoid giving these drugs?

61
Q

what does hypersensitivity reaction “drug fever” present as?

A

fever, arthropathy, epistaxis, hepatopathy, KCS, uveitis, skin eruptions of various types
- may be due to toxic metabolites- genetic component?

62
Q

what drugs do you want to avoid giving to doberman pinschers?

A
63
Q

sulfonamides have severe rxns in what breeds?

A

dobies

64
Q

how do you typically dose sulfonamides?

A

initiate therapy with a “priming dose” and then give maintenance doses that are 1/2 of the priming dose at intervals that are equal to the half life of the drug

65
Q

how should you administer sulfonamides?

A

IV! because of alkalinity of parenteral formulas

66
Q

what are indications for use of sulfonamides?

A

toxoplasmosis, chlamydiosis, chronic colitis
respiratory, genitourinary and soft tissue infxns are common indications

67
Q

how are diaminopyrimadines different than sulfonamides?

A

they interfere with folic acid production like sulfonamides, but via a different mechanism: they inhibit dihydrofolate reductase (DFR) enzyme

68
Q

why are diaminopyrimidines and sulfonamides often used together?

A

they inhibit sequential steps in the folic acid production pathway = synergistic activity
individually they are bacteriostatic, together are bactericidal

69
Q

trimethoprim is what kind of drug?

A

diaminopyrimadine
almost always used in combo w sulfonamides

70
Q

diaminopyrimadines

A

trimethoprim, ormetoprim, pyrimethamine
by themselves have fairly broad spectrum of activity
almost exclusively given in combo w sulfonamides

71
Q

potentiated sulfonamides

A

sulfonamide + trimethoprin
combinations are bactericidal and synergistic

72
Q

what is the formulation of potentiated sulfonamides?

A

usually in ratio of 1:5 trimethoprin:sulfonamide
1:20 ratio is optimal, but is much lower bc of rapid excretion of trimethoprin

73
Q

rifampin MOA

A

inhibition of RNA synthesis by binding the B-subunit of DNA-dependent RNA polymerases

74
Q

adverse effects of rifampin

A

liver and GI. monitor liver enzymes in dogs!

75
Q

rifampin is good for treating what?

A

intracellular bacteria like Mycobacterium (tuberculosis)
- active in Gm+ bacteria and intracellular penetration
- effective against Staph, Rhodo, and MRSA

76
Q

why are combinations of rifampin commonly used?

A

a single mutation of the amino sequence of the Beta subunit can lead to resistance

77
Q

treatment of choice for Rhodococcus equi in foals

A

rifampin

78
Q

oxazolidinones

A

super important for methicillin-resistant Staph and resistant enterococci!

79
Q

MOA of oxazolidinones

A

blocks protein synthesis: binds to site on 23S ribosomal RNA of 50S subunit

80
Q

how often are oxazolidinones used

A
  • adverse effects not reported
  • used to be expensive, but generic forms have lowered cost
  • should be used sparingly based on susceptibility testing, not rec’d for routine use
81
Q

what drug should NOT be used with sulfonamides?

A

methenamine: forms insoluble precipitates

82
Q

methenamine should not be given with what drugs? why?

A

sulfonamides: forms insoluble precipitates

83
Q
A
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Pharmacology Final (9 decks)

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