Antibacterial Drugs - Dermatology

Question 1

How can I curb MRSP and MRSS infections?

Answer 1

Appropriate use
Don't over use fluoroquinolones
Culture & Sensitivity
Hand washing/post-glove removal
Client hygiene
Topical therapy

Question 2

Baytril

Answer 2

Fluoroquinolone: Enrofloxacin is a fluoroquinolone antibiotic sold by the Bayer Corporation under the trade name Baytril. Enrofloxacin is currently FDA-approved for treatment of individual pets and domestic animals in the United States. In September 2005, the FDA withdrew approval of Baytril for use in water to treat flocks of poultry, as this practice was noted to promote the evolution of fluoroquinolone-resistant strains of the bacterium Campylobacter, a human pathogen. Fluoroquinolones such as ciprofloxacin are widely used in the treatment of human disease.

Question 3

Benefit of using topical therapy

Answer 3

Avoids MRSP/MRSS
More rapid lesion resolution
Reduces the duration of systemic antibiotic treatment if additionally necessary
May be used solely in mild/moderate infections
Chlorhexidine is most effective (benzoyl peroxide is less, and acetic acid-boric acid isn’t great)

Question 4

When do you use Fluoroquinolone?

Answer 4

Only use for gram -ve bacteria (pseudomonas etc)

Question 5

Antibiotic shampoos to use

Answer 5

Chlorhexidine is most effective (benzoyl peroxide is less, and acetic acid-boric acid isn’t great)

Question 6

The antibiotic selection depends on what 7 things?

Answer 6

• The route and frequency of administration
• Cost
• Animal species
• Safety
• Patient specific factors
• Duration of treatment
• Availability
  (Empirical selection vs. selection based on the results of bacterial culture and sensitivity testing)

Question 7

Empirical therapy should be reserved for the following situations:

Answer 7

• Non-recurrent infections
• Recurrent skin infections (without prior exposure to multiple antibiotic classes)
• Pending the results of bacterial culture and sensitivity testing
• Where initial treatment has been limited to topical antibacterial
  therapy alone
  Bacterial culture and sensitivity testing is NEVER contraindicated!

Question 8

Cultures and sensitivity testing is essential in the following situations:

Answer 8

• Poor response to 2 weeks of appropriate empirical systemic antibiotic therapy
• Emergence of new lesions 2 weeks or more after initiation of such therapy
• Presence of residual lesions after 6 weeks of therapy combined with skin cytology demonstrating infection with cocci
• Recurrent skin infections (prior exposure to multiple antibiotic classes)
• Whenever skin cytology demonstrates intracellular rods

Question 9

Cultures and sensitivity testing should be obtained in the following situations:

Answer 9

• When factors linked to nosocomial infections (acquired from veterinary hospitals) are present. These factors include:
• Long hospitalization stays (typically for a surgery)
• Induced immunosuppression with chemotherapy
• The use of injectable and oral antibiotics
  Antimicrobial exposure and hospital exposure are associated with MRSP infections in dogs, but primary community-onset cases in the absence of antimicrobial exposure or hospitalization can occur!

Question 10

Impact of antibiotics on microflora

Answer 10

All antibiotics are capable of altering the normal gastrointestinal microflora by eliminating sensitive microorganisms
This is particularly true when antibiotic are administered orally
This is usually of little or no clinical significance, however, it may lead to bacterial overgrowth of a resistant species, vomiting, soft stools, diarrhea and flatulence
First-line antibiotics target Staphylococcus pseudintermedius primarily with a minimal impact on the normal gastrointestinal microflora

Question 11

First line antibiotics include (6)

Answer 11

first generation cephalosporins, cefovecin, clindamycin, trimethoprim-sulfamethoxazole, doxycycline and minocycline

Question 12

When do you use second line antibiotics

Answer 12

Second/third line and last resort antibiotics should always be selected based on the results of bacterial culture and sensitivity testing
Second-line antibiotics (chloramphenicol, rifampin) are reserved for the treatment of meticillin-resistant staphylococcal infections

Question 13

First vs. second & third line antibiotics

Answer 13

.

Question 14

second line antibiotics examples

Answer 14

(chloramphenicol, rifampin)

Question 15

When do you use third line antibiotics

Answer 15

reserved for infections associated with Gram-negative bacteria and should not be used for the routine treatment of meticillin-sensitive staphylococcal pyoderma as they select for meticillin resistance

Question 16

Third line antibiotics examples

Answer 16

(fluoroquinolones)

Question 17

Potentialted Sulfonamides (first line) - biggest issue with toxicity

Answer 17

Can cause Keratoconjunctivitis sicca (irreversible, destruction of lacrimal glands, monitor tear production q1-2w if treatment exceeds 2 weeks, discontinue treatment if Schirmer tear test is < 15 mm/min or if there is > 50% decrease in tear production)

Question 18

Potentialted Sulfonamides (first line) - other issues with toxicity

Answer 18

Occasionally causes GI adverse effects (anorexia, vomiting, soft stools, diarrhea, flatulence)
Hypersensitivities (not dose dependant, avoid long-term administration, cutaneous adverse reaction, fever)

Question 19

Doxycycline Toxicity

Answer 19

Rarely causes GI adverse effects (anorexia, vomiting, soft stools, diarrhea, flatulence)
Oesophageal strictures in cats (from a broken tablet or incompletely dissolved capsule causing hydrochloride prolonged contact with the oesophageal mucosa due to slow transit through the oesophagus). This problem may be alleviated by administration of tablets and capsules with a water ‘flush’ or immediate feeding to ensure that the medication passes to the stomach
Doxycycline has little affinity for calcium and does not cause the dental enamel (teeth) discolouration seen with other tetracyclines in young animal

Question 20

Chloramphenicol Toxicity - most important

Answer 20

Prolonged use may cause bone marrow suppression

Question 21

Chloramphenicol Toxicity

Answer 21

Commonly causes GI adverse effects (anorexia especially in cats, vomiting, soft stools, diarrhea, flatulence)
Prolonged use may cause bone marrow suppression
Reversible dose and time-dependent anemia (dogs>cats) > neutropenia
Monitor CBC q2-4w if treatment exceeds 2 weeks
Have owners monitor the color of the gums and conjunctiva daily. Tell them to discontinue use immediately if these get pale

Question 22

Rifampin (aka rifampicin, 2nd line) toxicity

Answer 22

Occasionally causes GI adverse effects (anorexia, vomiting, soft stools, diarrhea, flatulence)
Liver injury (hepatoxicity) is the most common adverse reaction (20% of dogs develop increases in liver enzymes, and some dogs develop hepatitis)
Death-inducing hepatic necrosis is very rare!
Hemolytic anemia, thrombocytopenia > neutropenia
Monitor liver enzymes (esp. ALP) and CBC q1-2w if treatment exceeds 20 days

Question 23

Aminoglycocides toxicity

Answer 23

Aminoglycosides-induced acute kidney injury (AKI, tubular nephrotoxicity)
Cationic charge of aminoglycosides is attracted to the anionic charge of the phospholipids in the cell membrane (proximal tubular cells). Inside the cell the drug accumulates in lysozymes, causing lysosomal enzymatic release and destruction of the cell (tubular necrosis) and resulting in polyuric renal failure. Further destruction causes decrease in urine production and acute oliguric renal failure. Continued use results in the irreversible loss of the nephron.
Ototoxicity (cochlear hair cells of the inner ear are susceptible to the toxic effects of aminoglycosides, especially in cats; hearing loss is irreversible)

Question 24

Polymyxin B is never a good choice for… what w.r.t. Topical administration * EXAM Q*

Answer 24

Staph infections –> cannot penetrate this bacteria so really only works on gram -ve bacteria

Question 25

Chlorhexidine is a good choice for what topically?

Answer 25

Staph infections.

Question 26

Surolan

• works against?
• doesn’t work well against?

Answer 26

• Miconazole (the antifungal azole in Surolan) has an
excellent activity against Malassezia pachydermatis
• You will read that this product can be used against Staphylococcus aureus BUT….
• Polymyxin B is a polypeptide antibiotic that exerts bactericidal effect by increasing permeability of the bacterial cell membrane via chelation of membrane phospholipid components, leading to osmotic damage
• Polymyxin B only really works on gram negative bacteria (like Pseudomonas spp.

Question 27

Why doesn’t polymyxin B/Surolan work on gram +ve bacteria

Answer 27

• The reason why Polymyxin B has little to no effect on gram positive bacteria (like Staphylococcus spp.) is that the cell wall of these bacteria is too thick to permit access to the membrane
• Regardless,themostcommonlyisolatedpathogenin canine bacterial otitis externa is Staphylococcus pseudintermedius, not S. aureus (‘human staph’)
• In addition, the normal bacterial microflora of the ear canals is also mostly composed of S. pseudintermedius

Question 28

Principles for treating bacterial otitis

Answer 28

• First-linetopicalantibioticsareantibioticsthattarget Staphylococcus pseudintermedius or Pseudomonas aeruginosa primarily
• They can be selected empirically (based on cytology) or based on the results of bacterial culture and sensitivity testing
• Second-line topical antibiotics should ideally be selected based on the results of bacterial culture and sensitivity testing

Question 29

Treating bacterial otitis - be careful of…

Answer 29

Think twice before using topical and oral fluoroquinolones for staphylococcal infections!

Question 30

LO1

Answer 30

 Know that over the past decade, the veterinary community has faced a dramatic increase in antibiotic resistance within the species of bacteria responsible for canine bacterial pyoderma and bacterial otitis externa

Question 31

LO2

Answer 31

 The emergence of meticillin-resistant Staphylococcus infections continues to grow worldwide in both general and specialty small animal practices

Question 32

LO3

Answer 32

 This is particularly problematic within referral dermatology practice where it is not unusual to encounter staphylococci resistant to all ß-lactam antibiotics, potentiated sulfonamides, clindamycin, fluoroquinolones, doxycycline and chloramphenicol. In some cases, these resistance patterns may limit the therapeutic choice to rifampin and drugs of the aminoglycoside class

Question 33

 Know what you can do to curb the global pandemic of MRSP

and MRSS skin infections

Answer 33

a

Question 34

Remember that prudent antimicrobial use is an important measure all practitioners should strive towards to help reduce the growing prevalence and impact of these pathogens

Answer 34

a

Question 35

Know the factors to take into consideration for systemic antibiotic selection

Answer 35

a

Question 36

Know when you should obtain skin bacterial cultures for sensitivity testing

Answer 36

a

Question 37

 Understand the concept of first, second and third line

antibiotics for the oral treatment of bacterial pyoderma

Answer 37

a

Question 38

 Be particularly aware of the adverse effects, limitations and precautions when using potentiated sulfonamides, chloramphenicol, doxycycline (cats), rifampin and amikacin

Answer 38

a

Question 39

Understand the concept of first and second line antibiotics for the topical treatment of bacterial otitis

Answer 39

a

Question 40

 Know the mechanism of action of polymyxin B and remember this active ingredient is NEVER a good choice for Staphylococcal otitis

Answer 40

a

Question 41

What are some of the things to consider before choosing an oral antibiotic for the treatment of canine pyoderma:

a. Duration of treatment
b. Cost of treatment
c. Route and frequency of administration d. Adverse effects of treatment
e. All of the above

Answer 41

e. All of the above