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MeThicillin-ResisTanT sTaPhylococcal infecTions | Table 1. Systemic Antimicrobial Therapy for Dogs and Cats: Methicillin-Resistant Staphylococcal Infection DRUG DOSE / ROUTE / INTERVAL Amikacin 15–20 mg/kg IV or SC Q 24 H Chloramphenicol 50 mg/kg Po Q 8 h (dogs) 50–100 mg (total) Po Q 12 h (cats) Clindamycin 10 mg/kg Po Q 12 h 11 mg/kg PO Q 24 H Doxycycline 5–12 mg/kg Po Q 12 h Enrofloxacin 5–20 mg/kg PO Q 24 H (dogs) 5 mg/kg (maximum dose) Po Q 24 H (cats) Erythromycin 10–15 mg/kg Po Q 8 h Lincomycin 22 mg/kg Po Q 12 h Marbofloxacin 2.75–5.5 mg/kg PO Q 24 H Minocycline 5–12 mg/kg Po Q 12 h OrmetoprimSulfadimethoxine Day 1: 55 mg/kg Po following days: 27.5 mg/kg Po Q 24 H Rifampin§ 5–10 mg/kg PO Q 12–24 H TrimethoprimSulfamethoxazole 15–30 mg/kg Po Q 12 h Note: Antimicrobial selection should be based on culture and susceptibility. § rifampin monotherapy should be avoided if possible. between systemic antimicrobial therapy and acquisition of methicillin-resistant strains, topical antimicrobial or antiseptic therapy for the treatment of canine pyoderma, especially for first-time, mild, or localized infections, is recommended.31 RESISTANT INFECTION THERAPY Table 1 lists antimicrobial options and dosing regimens for methicillin-resistant staphylococcal pyoderma, based on culture and susceptibility. Treatment Duration Recommended treatment duration for methicillin-resistant staphylococcal infections does not necessarily exceed that recommended for methicillin-susceptible infections, which is the case, for example, for methicillin-susceptible staphylococcal pyoderma:58 • Superficial infections should be treated for a minimum of 3 to 4 weeks; then 1 week past clinical resolution • Deep infections should be treated for a minimum of 6 to 8 weeks; then 2 weeks past clinical resolution. Clinical resolution of MRSP-associated pyoderma may take longer than resolution of MSSP-associated pyoderma, but this is more likely due to empiric treatment failure, infection chronicity, or secondary pathologic changes to the skin rather than increased virulence of methicillinresistant strains.59 Systemic Therapy Systemic antimicrobial options for treatment of methicillin- and multidrug-resistant staphylococcal infections are often limited to: • Aminoglycosides, particularly amikacin • Chloramphenicol • Rifampin. When prescribed for extended therapy, potential adverse effects of these medications must be considered (see Table 2). use.24 Due to frequent resistance in methicillin-resistant strains, especially MRSP, practitioners should be aware for the potential of empiric failure with these antimicrobials; changes in therapy should be based on culture and susceptibility results. • Use of systemic fluoroquinolones for treatment of staphylococcal infections Table 2. Potential Adverse Effects of Systemic Antimicrobial Therapy should be reserved for cases in which: anTiMicRoBial PoTenTial aDVeRse effecTs » In vitro susceptibility is Amikacin • nephrotoxicity due to proximal tubular necrosis demonstrated • Ototoxicity » A f luoroquinolone is considered t he most Chloramphenicol • irreversible pancytopenia (humans) appropriate antimicrobi• Dose-dependent bone marrow suppression (dogs and cats) al choice for the patient. • Gastrointestinal upset, inappetence, weight loss Empiric use of fluoroqui• Drug interactions via inhibition of hepatic cytochrome P450 nolones is NOT recommicroenzymes mended due to the potenRifampin • Rapid resistance development when used alone tial for therapeutic failure • Severe, potentially fatal hepatotoxicity if the infection is caused • Gastrointestinal upset by methicillin-resistant • Hemolytic anemia, thrombocytopenia strains, which frequently • Orange discoloration of body fluids exhibit coresistance to flu• Drug interactions via induction of hepatic cytochrome P450 microenzymes oroquinolones. Due to t he connection May/June 2013 Today's Veterinary Practice 29