Managing MRSA, MRSP, and MRSS dermatologic infections in pets - Veterinary Medicine
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Managing MRSA, MRSP, and MRSS dermatologic infections in pets
Has one of these resistant infections invaded one of your patients? What should you do now to eliminate the infection? Read on...


Infected animals

Routine infections. Localized methicillin-resistant infections may be treated with topical medications such as chlorhexidine sprays or flushes, fusidic acid, or mupirocin applied twice daily until resolution. In cases of generalized pyoderma caused by methicillin-resistant staphylococci, always use aggressive topical antimicrobial therapies; in some cases, frequent (every one to two days) antibacterial (i.e. chlorhexidine) shampoos or conditioners and twice-daily antibacterial sprays (chlorhexidine, hypochlorous acid [Vetericyn—Innovacyn Inc.]) can resolve infection. A recent study comparing in vitro efficacy of antimicrobial shampoos found chlorhexidine to be superior in killing bacteria compared with benzoyl peroxide, ethyl lactate, and chloroxylenol.9

Figure 6A & 6B. Pemphigus foliaceus complicated by a severe MRSP pyoderma and otitis.

Figure 6B.

Refractory or severe infections. In refractory or severe pyoderma cases, systemic antibiotic therapy is used in combination with topical therapies (Figures 6A & 6B). Because of the variability of methicillin-resistant isolates, antibiotic choice should always be based on in vitro antibiotic susceptibility testing.10 Never treat methicillin-resistant infections with beta-lactam antibiotics (penicillins and cephalosporins), even if in vitro testing implies susceptibility. This is because methicillin resistance means resistance to all beta-lactams, but laboratory reporting errors can occur and erroneously imply sensitivity where it does not exist.11 For superficial pyoderma (whether methicillin susceptible or methicillin resistant), antibiotics are required for at least three weeks (one week beyond complete healing); for deep pyoderma, antibiotics may be needed for four to eight weeks or longer (or two to three weeks beyond complete healing) (Figures 7A & 7B).

Rechecks every two to four weeks are important to evaluate response to treatment, make treatment modifications if needed, and evaluate when antimicrobial therapy can be stopped. Depending on the bacterial strain, antibiotics that may be effective in methicillin-resistant infections include

  • Chloramphenicol
  • Aminoglycosides
  • Potentiated sulfonamides
  • Clindamycin (only use if sensitivity to erythromycin is also indicated or a test for inducible clindamycin resistance has been performed)
  • Doxycycline (but if sensitivity testing indicates resistance to tetracycline, then doxycycline may not be effective in vivo even if in vitro sensitivity is indicated1 )
  • Minocycline
  • Rifampin
  • Fluoroquinolones

Figure 7A & 7B. Deep ulcers and draining lesions caused by immune mediated panniculitis complicated by MRSP.

Figure 7B.

Use of fluoroquinolones for the treatment of methicillin-resistant pyoderma is not recommended except as a last resort since, with the exception of moxifloxacin, they have the potential to select for high-level methicillin-resistant mutants (which are not only resistant to fluoroquinolones but also to other antibiotics).12,13 If fluoroquinolones are used, then veterinary-labeled products (which have near complete bioavailability)14 are recommended to be used at the high end of the label dose range.15

Use of ciprofloxacin may lead to treatment failure because of inconsistent absorption of this drug in dogs (in one study the oral absorption of ciprofloxacin in dogs varied from 28% to 98%),16 thus it is not recommended. Additionally, the use of vancomycin (administered intravenously only since oral vancomycin is not systemically absorbed) or linezolid for treating methicillin-resistant infections in animals is controversial and not recommended, as these drugs are often the last resort in human medicine.1

Finally, drugs for treating MRSA in human medicine include the streptogramins (quinupristin and dalfopristin), daptomycin, tigecycline, and ceftaroline fosamil; all are administered intravenously, and their use in animals has not been reported.17


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