Page 1530 - Clinical Small Animal Internal Medicine

1468 Section 12 Skin and Ear Diseases

occurred via acquisition of the mecA gene from human Treatment of Pyodermas
VetBooks.ir staphylococci and subsequent selection of resistant Appropriate management of staphylococcal pyoderma is
strains via widespread use of beta‐lactam antimicrobi-
als. Methicillin‐resistant canine and feline cutaneous
infections and colonization have been subsequently an active area of investigation, which may result in future
changes in systemic antimicrobial dose and duration.
reported worldwide, with MR S. pseudintermedius
most commonly seen. Prevalence varies by geographic
location. Systemic Therapy
Frequent antimicrobial treatment is a risk factor for Systemic antimicrobial therapy is indicated for regional,
canine MR staphylococcal pyoderma and carriage of MR generalized or severe superficial bacterial folliculitis,
staphylococci in healthy dogs and cats. Risk factors asso- mucocutaneous pyoderma, and forms of deep staphylo-
ciated with MR S. aureus infection in the dog and cat coccal pyoderma. For milder presentations, expected
include frequent antimicrobial courses, frequent veteri- time of resolution with systemic therapy is 14–28 days.
nary visits, multiple days of hospitalization, and the pres- Duration of therapy may be longer and treatment for one
ence of surgical implants. week beyond clinical resolution is recommended. For
deep pyoderma, treatment may take 6–12 weeks to
Recognition of Methicillin Resistance achieve visual and palpable resolution. For severe pres-
entations of deep pyoderma, consider continuation of
Methicillin‐resistant and MDR staphylococcal pyo- antimicrobial therapy four weeks beyond palpable reso-
derma cases do not typically possess unique clinical lution to prevent relapse. Importantly, all patients receiv-
features. Rather, the first indication of resistance is ing antimicrobial therapy for staphylococcal pyoderma
lack of response to empirical antimicrobial therapy. must be periodically rechecked (every 2–4 weeks) prior
Therefore, to ensure appropriate response, all patients to conclusion of antimicrobial treatment to ensure
must be reexamined prior to conclusion of antimicro- appropriate response.
bial treatment. If resistance is suspected, perform a
cytologic evaluation to assess for the presence of cocci, Empirical and Culture‐Based Therapy
as well as bacterial culture and sensitivity. A sterile nee- Rational antibiotic options for empirical treatment of
dle is used to rupture a pustule or lift the edge of an staphylococcal pyoderma include cephalexin (22–30 mg/
epidermal collarette or crust to reveal exudate. The kg PO q12h), amoxicillin/clavulanate (13.75 mg/kg PO
sample is collected with a sterile swab. For cases of pap- q12h), cefpodoxime (5–10 mg/kg PO q24h), and cefo-
ular or nodular pyoderma, punch biopsies are recom- vecin (8 mg/kg SC q14 days). Lincomycin (15–25 mg/kg
mended for culture. PO q12h) and clindamycin (5.5–10 mg/kg PO q12–24h)
Although “methicillin resistance” is the accepted term, are considered first‐line choices, but their conservation
the more stable oxacillin is used as a surrogate in the is recommended as some MR and MDR staphylococcal
laboratory for methicillin susceptibility. Resistance to strains retain susceptibility to these antimicrobials. For
oxacillin is a strong indicator of mecA acquisition and cases of resistant pyoderma, clindamycin should be used
resistance to all beta‐lactam antibiotics. Upon interpret- with reservation if the laboratory has not tested for
ing antibiograms, it is important to recognize that oxa- inducible resistance (D‐test). This test should be
cillin‐resistant staphylococci may show in vitro sensitivity requested if erythromycin resistance is present. If this
to other beta‐lactams. Thus, interpretation of staphylo- test is not available and the bacterial strain is resistant to
coccal antibiograms should first involve noting oxacillin erythromycin but susceptible to clindamycin, do not
susceptibility, rather than simply searching for reported prescribe the latter.
susceptible antimicrobials. If a bacterial strain is resist- Culture and sensitivity‐based selection of a systemic
ant to oxacillin, it should be considered resistant to all antimicrobial is indicated for patients that fail to clini-
beta‐lactam antibiotics. cally respond to empirical therapy, have evidence of deep
Direct the laboratory to perform extended antimicro- pyoderma, or have a chronic history of antimicrobial use
bial panels for suspected resistance. Additionally, species with unknown or lackluster response. Empirical treat-
identification of staphylococci is useful, as MR S. aureus ment is not recommended in these cases as staphylococ-
has a more significant zoonotic implication given that it cal antimicrobial resistance patterns are unpredictable.
is host‐adapted to humans. Methicillin‐resistant, coagu- Dwindling rational systemic treatment options for MDR
lase‐negative staphylococci, including S. schleiferi subsp. staphylococcal pyoderma present a global practical chal-
schleiferi, are clinically significant and should not be lenge. A 2010 study examining 103 isolates of MRSP in
disregarded. North America reported that nearly 90% of isolates were