Today's Veterinary Practice

MAY-JUN 2014

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Today's Veterinary Practice May/June 2014 48 | DermaTology DeTails tvpjournal.com owners are willing and able to bathe more frequently, they should be encouraged to do so. They can augment their bathing with the use of rinses, sprays, leave-on condition- ers, mousses, and wipes in between baths. Systemic Antibiotics Modern recommendations for antibiotic selection suggest that we: • Consider efficacy, safety, and compliance • Use those that are best in class. Traditionally, we have been taught to select older gener- ation, less active antibiotics based on the belief that if the antibiotic fails, we can then use newer, more active com- pounds. However, this principle can no longer be applied in the age of staphylococcal methicillin resistance—once the less active, beta-lactam antibiotics become ineffective, the entire class is useless for systemic therapy. Most dermatologists believe that the most appropriate first-choice antibiotic for canine pyoderma is a cephalo- sporin and, in most patients, treatment with cephalospo- rins may be empirical. If a pyoderma fails to resolve with a cephalosporin, it is important to step back and re-evaluate the diagnosis and treatment plan. If cytology from lesions of pyoderma identifies rods, sus- picion is raised for a Pseudomonas or other gram negative pyoderma. The empirical choice of antibiotic in these pa- tients is a fluoroquinolone. However, infections with rod- shaped bacteria should be cultured to verify: 1. What bacteria are present 2. Which antibiotic (if any) is indicated. Table 2 (page 46) contains a list of antibiotics and doses used to treat canine pyoderma. WHAT IS METHICILLIN RESISTANCE, AND HOW DO WE RECOGNIZE IT? Genetic Development Methicillin resistance in Staphylococci is associated with acqui- sition of a gene, mecA, that is incorporated into the bacterial genome and subsequently passed on to all daughter cells. 22-24 • MecA encodes for a mutated form of penicillin-binding protein on the bacteria's surface. • This mutant protein cannot bind any beta-lactam antibiotic; therefore, all penicillins and cephalosporins are ineffective. • The genetic element on which the mecA gene resides can also carry other antibiotic-resistant genes, and some S pseudintermedius will be resistant to all antibiotics tested. • This genetic element is retained within the Staphylo- coccus as long as antibiotic pressure is present. If antibi- otic pressure is removed, the bacteria have the potential to excise the incorporated genetic element and become sensitive again. • For this reason, it may work best to avoid systemic A Figure 2. Results of daily washing with 3% to 4% chlorhexidine shampoo in 10 dogs with superficial pyo- derma: A scoring system consisting of pruritus, erythe- ma, crusting, and hair loss was used, with each compo- nent graded from 0 to 3 based on severity; at 2 weeks, all dogs showed 50% or more improvement, with 3 dogs demonstrating complete resolution, and at 4 weeks, all pyoderma lesions were resolved except for 1 dog, which was still pruritic due to uncontrolled atopic dermatitis (A). Image of patient with superficial pyoderma prior to treat- ment with daily baths (B), and at the end of treatment, with all pyoderma resolved and hair regrowth seen (C). Score B C Many methicillin-resistent staphylococcal infec- tions are also multi-drug resistant —in these types of infections, the bacteria have acquired resistance fac- tors to antibiotics other than beta-lactams, complicating treatment and limiting therapeutic options. TVP_2014-0506_DermDetails_Infections.indd 48 5/23/2014 3:24:57 PM

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