Page 1471 - Small Animal Internal Medicine, 6th Edition

CHAPTER 92 Practical Antimicrobial Chemotherapy 1443

clinical signs of disease and trophozoites. However, ronida- Dogs or cats with apparent bacteremia or sepsis from
zole resistance and treatment failures have been detected enteric bacteria should be treated with parenteral antibiotics
VetBooks.ir (Xenoulis et al., 2013). CNS toxicity is also common with with a spectrum against anaerobic and gram-negative organ-
isms. The combination of enrofloxacin with a penicillin or
ronidazole if overdosed. Fluoroquinolones may be effective
in T. foetus infected cats that fail to respond clinically to
cephalosporins or imipenem are also appropriate choices.
ronidazole. metronidazole is generally effective. Second-generation
Most dogs or cats diagnosed with cryptosporidiosis are The most common bacteria in one study of hepatic infec-
infected by C. canis or C. felis, respectively. Although infec- tions were E. coli, Enterococcus, Streptococcus, Clostridium,
tion with these host-adapted species is common, it is unclear and Bacteroides (Wagner et al., 2007). Dogs or cats with
how many infected dogs and cats actually have diarrhea hepatic infections and signs of bacteremia should be treated
directed related to the infection. Infection studies of healthy with antibiotics that kill gram-positive, gram-negative, and
dogs or cats rarely induce diarrhea. Thus, if other potential anaerobic bacteria, as previously discussed. Bacteremic
causes of diarrhea, like Giardia spp., are detected in a dog or hepatic infections generally respond to amoxicillin-
cat positive for Cryptosporidium, the other cause of diarrhea clavulanate, first-generation cephalosporins, or metronida-
should be treated first to see if the diarrhea resolves. Antibi- zole; a fluoroquinolone should be added if signs of sepsis are
otic treatment does not eliminate Cryptosporidium spp. present. Decreasing numbers of enteric flora by oral admin-
infection; it just potentially lessens clinical signs. Tylosin istration of penicillins, metronidazole, or neomycin can
(10-15 mg/kg q12h PO) has apparently been successful in lessen the clinical signs of hepatic encephalopathy.
lessening diarrhea and oocyst shedding in cats and dogs with
diarrhea that were positive for Cryptosporidium. Azithromy-
cin at 10 mg/kg PO daily for 7 days may lessen diarrhea in MUSCULOSKELETAL INFECTIONS
some dogs or cats with cryptosporidiosis. If responding after
7 days, continue treatment for at least 1 week past clinical Osteomyelitis and discospondylitis are commonly associated
resolution. Nitazoxanide can be considered at 75 mg/kg, PO, with infections by Staphylococcus, Streptococcus, Proteus,
twice, 14 days apart in dogs with Giardia and Cryptospo- Pseudomonas spp., E. coli, and anaerobes (Siqueira et al.,
ridium co-infections (Moron-Soto et al., 2017). 2014). Recently, Bartonella spp. infections have also be iden-
The Toxoplasma gondii oocyst-shedding period can be tified in cats, dogs, and humans (Varanat et al., 2009). First-
shortened by administration of clindamycin, sulfadimethox- generation cephalosporins, amoxicillin-clavulanate, and
ine, or ponazuril. However, most cats have completed the clindamycin are logical antibiotics for empirical therapy of
oocyst-shedding period in 7 to 14 days, so treatment is not these conditions because of their spectrum of activity against
often needed. Cystoisospora spp. generally respond to the the gram-positive organisms and anaerobic bacteria, and
administration of ponazuril at 50 mg/kg, PO, daily for 3 days their ability to achieve high concentrations in bone (see
(Litster et al., 2014). Use of sulfadimethoxine, other sulfa- Table 92.6). Quinolones should be used if gram-negative
containing drugs, or clindamycin is generally not needed. organisms (including Brucella canis) or Bartonella spp. infec-
Diarrhea associated with enteric bacterial infections gen- tions are suspected. Antibiotic treatment should be contin-
erally will respond to dietary changes and administration of ued for a minimum of 2 weeks beyond resolution of
probiotics. If antibiotics are deemed necessary, C. perfringens radiographic changes. Repeated treatment may be required,
and bacterial overgrowth generally respond to treatment as bone infections can be difficult to eliminate.
with tylosin, amoxicillin, or ampicillin. Dogs or cats with Dogs and cats with septic polyarthritis should be treated
suspected campylobacteriosis or salmonellosis should have in the same way as those with osteomyelitis, and the source
fecal culture performed to determine antimicrobial sensitiv- of infection should be removed, if possible. Anaplasma
ity if other pets or people in the family become ill. GI signs phagocytophilum, E. ewingii, Bartonella spp., Borrelia burg-
of campylobacteriosis or salmonellosis are generally self- dorferi, Ehrlichia spp., L-form bacteria, Mycoplasma spp.,
limited with supportive care alone, so these infections are Rickettsia rickettsii, and other chronic infections can induce
often only treated parenterally and if systemic signs of disease nonseptic, suppurative polyarthritis from local infection in
(e.g., fever) exist because of rapid resistance that occurs after the joints or immune complexes. Occasionally, morulae of
oral administration of antibiotics. Appropriate antibiotics for A. phagocytophilum or E. ewingii are identified cytologically
the empirical treatment of salmonellosis while awaiting sus- in the joint fluid or in circulating neutrophils. In general, the
ceptibility testing results include ampicillin and trimethoprim- cytologic findings in joint fluid induced by these agents are
sulfonamide; quinolones are also effective. Visible Helicobacter similar to those of immune-mediated polyarthritis. For this
spp. infections were eliminated after administration of oral reason, doxycycline is a logical empirical antibiotic choice
metronidazole (11-15 mg/kg PO q12h), amoxicillin (22 mg/ for dogs with nonseptic, suppurative polyarthritis pending
kg PO q12h), and bismuth subsalicylate suspension (0.22 mL/ the results of further diagnostic tests. Amoxicillin and cefo-
kg PO q6-8h) for 3 weeks (Jergens et al., 2009). Boxer colitis vecin are alternative drugs for the treatment of B. burgdorferi
is likely associated with Escherichia coli and is generally infection (Wagner et al., 2015) but are not effective for the
treated with enrofloxacin administered at 10 mg/kg PO q24h treatment of most other infections associated with polyar-
for 8 weeks (Marks et al., 2011). thritis and so should be second choices to doxycycline.