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Dermatology > Therapy for Bacterial Disease > Flashcards

Therapy for Bacterial Disease Flashcards

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Dermatology Board Prep flashcards
1
Q

What might cause recurrent Staphylococcal pyoderma?

A
  • recurrent vs. persistent
    • > 2 weeks <
  • inappropriate therapy
    • dosage and length
  • look for underlying cause
    • Demodex
    • allergies
    • endocrine/metabolic
    • immunodeficiency (cats)
    • physical causes (trauma)
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2
Q

What is your approach to a recurrent wound or cellulitis?

A
  • best to culture
  • systemic therapy based on C&S
  • biopsy of intact nodule
  • large sample required to culture atypical mycobacteria
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3
Q

What cases should be cultured?

A
  • recurrent pyoderma
  • pyodermas that fail to respond to initial tx
  • deep pyodermas
    • chronic recurrent draining tracts
    • cellulitis
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4
Q

How should you culture a bacterial skin lesion?

A
  • look for primary lesion
    • papule
    • pustule
    • nodule
  • avoid secondary lesions, if possible
  • avoid ulcerated or opened lesions
  • stop abx 3-5d before culture
    • if possible - if not alert the laboratory
  • pustules - wipe surface w/ alcohol, open and swab
  • papules, plaques, nodules or draining tracts - clean surface and biopsy
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5
Q

What is the choice of antibiotics determined by?

A
  • empirical or based on susceptibility test
    • in vitro vs. in vivo
  • safety profile
  • concurrent dz
  • depth of the infection
  • length of the tx
  • needs to reach the skin in high concen.
  • breed
  • age
  • constraints of owner
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6
Q

What are general rules of therapy for bacterial skin disease?

A
  • use abx with narrow spectrum first
    • rapid resistance with some abx
  • use abx with less adverse effects
    • incr safety
  • if many bacteria isolated
    • select abx effective against various organisms
    • if not possible, focus on Staph first
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7
Q

What are the general rules of antibiotic therapy?

A
  • appropriate length of therapy
    • superficial pyoderma
      • minimum: 3-4 wks
      • abx continued for a minimum of 7-10d past resolution of C/S
    • deep pyoderma
      • minimum: 2-3 mo
      • abx continued for a min of 4 wks past resolution of signs
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8
Q

How do you monitor therapy for bacterial disease?

A
  • difficult with deep infections
    • rapid initial improvement
    • apparent “plateau” of improvement
    • granulomatous component
    • fibrosis and FB
  • topical tx is mandatory
    • antibiotic vs. antiseptic
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9
Q

What are common reasons for treatment “failure”?

A
  • failure to ID all underlying causes
  • wrong abx
  • inappropriate dose
  • inappropriate length of tx
  • concurrent use of steroids
  • foreing body rxn
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10
Q

What are the first tier antibiotics for pyoderma?

A
  • macrolides/macrolides-like
    • erythromycin
    • lincomycin
    • clindamycin
  • first generation cephalosporins
  • amoxicillin/clavulanic acid
  • potentiated sulfonamides
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11
Q

What are the second tier antibiotics for pyoderma?

A
  • third generation cephalosporins
    • cefpodoxime, cefovecin
  • doxycycline and minocycline
  • fluoroquinolones
  • chloramphenicol
  • rifampin
  • aminoglycosides
    • gentamycin and amikacin
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12
Q

What are the third tier antibiotics for pyoderma?

A
  • vancomycin
  • linezolid
  • teicoplanin
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13
Q

Describe beta-lactam antibiotics

A
  • first tier antibiotic
  • penicillins
    • beta lactamase resistant penicillins
      • oxacillin
      • dicloxacillin
      • dafcillin
    • potentiated penicillins
      • amoxicillin/clavulanic acid
      • ampicillin/sulbactam
    • cephalosporines
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14
Q

What three first tier antibiotics are beta-lactamase susceptible?

A
  • ampicillin
  • amoxicillin
  • penicillin
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15
Q

Describe amoxicillin/clavulanic acid

A
  • broad spectrum
    • primarily gram +
  • bactericidal
  • rapid absorption
  • dose: 22 mg/kg q12
  • adverse effects: GI
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16
Q

Describe Cephalosporins

A
  • broad spectrum bactericidal; work by inhibition of synthesis of bacterial cell wall
  • first generations:
    • Cephalexin
      • used by many as first line antibiotic
      • broad spectrum but primarily gram +
      • resistance increasingly reported
      • t1/2 = 6.5hrs
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17
Q

Describe the adverse effects of cephalexin

A
  • vomiting, diarrhea
  • IMHA
  • immune mediated thrombocytopenia
  • urticaria
  • drug eruptions
  • rarely: neurotoxicity, neutropenia, interstitial nephritis
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18
Q

Describe methicillin resistant staphylococci

A
  • NOT more virulent than MSS
  • MORE difficult to treat
  • Activation of the gene mecA
    • incr penicillin binding protein 2a
    • involved in the synth of peptoglycans in bacterial wall
    • resistance to ALL beta lactams
    • oxacillin = class representative drug for in vitro testing
19
Q

Describe clindamycin

A
  • food does not interfere with absorption
  • good penetration in fibrotic tissues
    • intracellular accumulation
  • greater efficacy than amox/clav. acid
  • very well tolerated
    • esophageal strictures (cats)
  • good choice for methicillin resistant Staph and superficial pyoderma
20
Q

Describe erythromycin

A
  • absorption
    • incomplete
    • inactivated by gastric secretions
    • delayed by food admin
  • soluble in lipids
    • 75% bound; eliminated via excretion in bile
  • inhibition of cytochrome P450
    • ​drug interactions
  • adverse effects: GI
  • macrolide; inhibits ribosomal protein synthesis
  • bacteriostatic; efficacy is time-dependent
  • T1/2 = 2 hr
  • narrow spectrum: ideal for Staph
  • effective in 80% cases
  • very expensive!
21
Q

Describe lincomycin

A
  • bacteriostatic
  • macrolide-like antibiotic
  • better absorption and distribution than erythromycin
  • give on empty stomach
  • rapid resistance (cross-reactive with erythromycin)
22
Q

Describe the clindamycin–macrolide interaction

A
  • macrolide-inducible resistance
    • inducible methylase that alters the common ribosomal binding site for macrolides, clindamycin and the group B streptogrammins
      • D-test
        • Erythomycin and clindamycin
23
Q

Describe potentiated sulfonamides

A
  • work by interfering with synthesis of folic acid
    • bacteriocidal
  • effective in 50-80% cases
  • anti-acids interfere with absorption
24
Q

What are some potential issues with sulfa group antibiotics?

A
  • they are very allergenic and may trigger hypersensitivity reactions
    • Type I-III
25
Q

What are some adverse effects of potentiated sulfonamides?

A
  • anemia, leukopenia, thrombocytopenia
  • fever
  • KCS
  • hepatopathy
  • nitrous metabolite is cytotoxic
  • arthropathy
  • cutaneous eruptions
  • hypothyroidism
  • polymyositis
26
Q

What breeds should you not use potentiated sulfonamides?

A
  • do not use in Dobies and Rotties
    • incr risk of arthropathy
    • mechanism unknown
    • possible defect of detoxification
27
Q

Describe silver sulphadiazine

A
  • topical sulfonamide
  • broad spectrum
  • ideal for Pseudomonas spp.
  • 1% for skin
  • 0.1% suspension in cases with ruptured ear drum
28
Q

Describe Doxycycline

A
  • 2nd tier antibiotic
  • used for resistant cases
  • time-dependent cases
  • currently very expensive, often substituted with minocycline
  • anti-inflammatory properties
  • adverse effects:
    • vomiting, diarrhea, nausea
    • yellow staining of teeth, esophageal strictures (cats)
29
Q

Describe Chloramphenicol

A
  • broad spectrum
  • bacteriostatic
  • works by inhibiting ribosomal protein synthesis
  • prescribed more and more frequently
  • metabolized by the liver
  • AE:
    • causes depression of microsomal enzymes
      • inhibits the metabolism of other drugs
    • aplastic anemai (irreversible) in owners
    • animals: GI, anorexia, elevated liver enzymes, anemia (reversible), peripheral neuropathy (large breeds)
30
Q

Describe cephalosporins

A
  • third generation
    • activity against S. pseudintermedius not superior to 1st generation
    • active against Gram -
    • potential selection for methicillin resistance; very expensive
  • e.g. Cefovecin, Cefopodoxime proxetil (Simplicef)
31
Q

Describe fluoroquinolones

A
  • broad spectrum
    • gram + and -
  • bactericidal
    • work by inhibiting DNA gyrase –> DNA replication
  • save it for resistant cases and/or gram - !!
  • absorption inhibited by anti-acids
    • chelates strong cations
  • great penetration in tissues
  • accumulate in neutrophils and macrophages
  • concentration dependent: important to use once daily high dose
  • peak concentrations are more important than duration of serum values > MIC
32
Q

What is the aim for the appropriate concentration of an antibiotic?

A
  • try to strive to reach the highest dose possible (above minimum inhibitory concentration and mutant selection window), achieving the mutant prevention concentration
    • the risk of selection for resistant mutants is virtually impossible above the MPC
33
Q

What are the adverse effects of fluoroquinolones?

A
  • GI
  • neurological
    • seizures (very uncommon)
  • arthropathy
    • stop growing plates
  • blindness
    • enrofloxacin (cats)
34
Q

Describe enrofloxacin

A
  • bioavailability = 40%
  • metabolized into ciprofloxacin
  • food administration incr amount of Cipro
  • expensive for large dogs
35
Q

Describe marbofloxacin

A
  • Bioavailability: 94%
  • T1/2: 14 hrs
  • Tmax: 2 hrs
  • Wide distribution
  • Plasma concentration > MIC for more than 24 hrs
36
Q

Describe Orbifloxacin

A
  • Tmax: 1 hr
  • Bioavailbility: 97%
  • Cmax in tissues in 6 hrs
  • 90% of drug is excreted metabolized in urines
37
Q

Describe Moxifloxacin

A
  • human product
  • used in dogs at 8 mg/kg q24h
38
Q

Describe Pradofloxacin (Veraflox)

A
  • 3rd generation enhanced spectrum veterinary antibiotic of the fluoroquinolone class
  • labeled for dogs (Europe) and cats (USA)
  • extensive ocular safety testing
39
Q

Describe Mupirocin

A
  • bacteriocidal
    • binds to tRNA
  • excellent for Staph infections
  • rare resistance
  • minimal systemic absorption
40
Q

Describe Polymixin B

A
  • Used for resistant Pseudomonas spp.
  • binds to the cell membrane and alter its structure, making it more permeable
    • the resulting water uptake leads to cell death
41
Q

What are the principles of antibiotic use?

A
  1. Full dosage!
  2. Adequate time!
  3. Treat Staphilococcus
  4. Avoid steroids if possible
  5. Re-evaluate if not improved
42
Q

What are the considerations you should have for long term antibiotic therapy?

A
  • not recommended
  • avoid pulse tx
  • consider all triggeringh factors before considering immune stimulation
43
Q

Describe topical therapy

A
  • important adjunct tx
  • Chlorhexidine
    • mildly irritant
    • bacteriocidal, fungicidal (yeast), virocidal
    • used for whirlpool tx
  • Benzoyl peroxide
    • excellent for staph infections
    • anti-pruritic, degreasing, keratolytic
      • potential irritation and dry skin
44
Q

Describe vetericyn spray

A
  • oxychlorine
  • used in humans for MRSA
  • two different strengths
  • water based
  • well tolerated

Dermatology (13 decks)

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