Therapy for Bacterial Disease Flashcards
(44 cards)
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)
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
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
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
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
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
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
- superficial pyoderma
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
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
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
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
12
Q
What are the third tier antibiotics for pyoderma?
A
- vancomycin
- linezolid
- teicoplanin
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
- beta lactamase resistant penicillins
14
Q
What three first tier antibiotics are beta-lactamase susceptible?
A
- ampicillin
- amoxicillin
- penicillin
15
Q
Describe amoxicillin/clavulanic acid
A
- broad spectrum
- primarily gram +
- bactericidal
- rapid absorption
- dose: 22 mg/kg q12
- adverse effects: GI
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
- Cephalexin
17
Q
Describe the adverse effects of cephalexin
A
- vomiting, diarrhea
- IMHA
- immune mediated thrombocytopenia
- urticaria
- drug eruptions
- rarely: neurotoxicity, neutropenia, interstitial nephritis
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
- D-test
- inducible methylase that alters the common ribosomal binding site for macrolides, clindamycin and the group B streptogrammins
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
What are some adverse effects of potentiated sulfonamides?
* anemia, leukopenia, thrombocytopenia
* fever
* KCS
* hepatopathy
* **nitrous metabolite is cytotoxic**
* arthropathy
* cutaneous eruptions
* hypothyroidism
* polymyositis
26
What breeds should you not use potentiated sulfonamides?
* do not use in Dobies and Rotties
* incr risk of arthropathy
* mechanism unknown
* possible defect of detoxification
27
Describe silver sulphadiazine
* topical sulfonamide
* broad spectrum
* ideal for Pseudomonas spp.
* 1% for skin
* 0.1% suspension in cases with ruptured ear drum
28
Describe Doxycycline
* _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
Describe Chloramphenicol
* 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
Describe cephalosporins
* 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
Describe fluoroquinolones
* 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
What is the aim for the appropriate concentration of an antibiotic?
* 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
What are the adverse effects of fluoroquinolones?
* GI
* neurological
* seizures (very uncommon)
* arthropathy
* stop growing plates
* blindness
* enrofloxacin (cats)
34
Describe enrofloxacin
* bioavailability = 40%
* metabolized into ciprofloxacin
* food administration incr amount of Cipro
* expensive for large dogs
35
Describe marbofloxacin
* Bioavailability: 94%
* T1/2: 14 hrs
* Tmax: 2 hrs
* Wide distribution
* Plasma concentration \> MIC for more than 24 hrs
36
Describe Orbifloxacin
* Tmax: 1 hr
* Bioavailbility: 97%
* Cmax in tissues in 6 hrs
* 90% of drug is excreted metabolized in urines
37
Describe Moxifloxacin
* human product
* used in dogs at 8 mg/kg q24h
38
Describe Pradofloxacin (Veraflox)
* 3rd generation enhanced spectrum veterinary antibiotic of the fluoroquinolone class
* labeled for dogs (Europe) and cats (USA)
* extensive ocular safety testing
39
Describe Mupirocin
* bacteriocidal
* binds to tRNA
* excellent for Staph infections
* rare resistance
* minimal systemic absorption
40
Describe Polymixin B
* 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
What are the principles of antibiotic use?
1. Full dosage!
2. Adequate time!
3. Treat Staphilococcus
4. Avoid steroids if possible
5. Re-evaluate if not improved
42
What are the considerations you should have for long term antibiotic therapy?
* not recommended
* avoid pulse tx
* consider all triggeringh factors before considering immune stimulation
43
Describe topical therapy
* 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
Describe vetericyn spray
* oxychlorine
* used in humans for MRSA
* two different strengths
* water based
* well tolerated
