Page 165 - Small Animal Internal Medicine, 6th Edition

CHAPTER 6 Acquired Valvular and Endocardial Disease 137

and cats with culture-negative endocarditis. Initial, empiric an oral fluoroquinolone is added. Currently recommended
broad-spectrum combination therapy for infective endocar- oral therapy for Bartonella infection includes doxycycline
VetBooks.ir ditis usually includes a β-lactam antibiotic such as a syn- (5-10 mg/kg q12h PO; or minocycline at 10 mg/kg q12h
PO), combined with enrofloxacin (5-20 mg/kg q24h PO)
thetic penicillin derivative (e.g., ampicillin [22-40 mg/kg IV
q6-8h], or ticarcillin/clavulanate [50 mg/kg IV q6h]) or a
for dogs in the United States) for 28 to 42 days (at least). In
cephalosporin (e.g., cefazolin [22-33 mg/kg IV q8h], or cef- or pradofloxacin (5-10 mg/kg q24[-12]h PO; not approved
triaxone [20 mg/kg IV q12h]), with either an aminoglyco- clinically stable Bartonella patients where initial IV therapy
side (amikacin [7-10 mg/kg IV q12h; or 20 mg/kg q24h], is not used, the recommendation has been made to start
with fluid support) or a fluoroquinolone (enrofloxacin oral treatment with one drug (e.g., doxycycline at 5 mg/
[5-10 mg/kg IV q12h]). The former provides a gram-positive kg q12h), followed in 5 to 7 days with the addition of the
spectrum and the latter, gram-negative. Clindamycin or met- second drug. However, this may not be possible in patients
ronidazole provides added anaerobic coverage. Antibiotics with endocarditis or myocarditis because of illness sever-
are best administered via IV for the first week or two to ity. This recommendation is based on the observation that,
obtain higher and more predictable blood concentrations. when both antibiotics are begun simultaneously for Bar-
Oral therapy can be used thereafter for the sake of practical- tonella infection, a reaction can occur within 4 to 7 days
ity, assuming clinical and laboratory abnormalities are (or longer) which may include lethargy, fever, and vomiting
improved. Empirical options for continued oral therapy (Jarisch-Herxheimer–like reaction). It is thought that the
include either amoxicillin/clavulanate (20-25 mg/kg PO reaction, which can last a few days, relates to acute bacterial
q8h) or cephalexin (25-30 mg/kg PO q8h), in combination injury or death and host cytokine release. Unless the patient’s
with enrofloxacin (2.5-5 mg/kg PO q12h). For multiple-drug clinical status continues to deteriorate from this reaction,
resistant bacteria requiring therapy with imipenem, SC the PO antibiotic strategy should be continued as planned
administration following an initial 1- to 2-week course of IV and supportive care given as appropriate. The addition of
administration has been recommended. In general, antimi- antiinflammatory doses of a glucocorticoid may be helpful
crobial therapy is continued for at least 6 weeks, although for patients experiencing this reaction; however, the gluco-
therapy for 8 weeks is often recommended. However, ami- corticoid should be discontinued after a few days as those
noglycosides are discontinued after 7 to 10 days or sooner if signs abate.
renal toxicity develops. Close monitoring of the urine sedi- For cats with cardiac Bartonella infection, initial therapy
ment is indicated to detect early aminoglycoside nephrotox- with amikacin (10-14 mg/kg q24h IV, IM, or SC) for 7 to 10
icity. Fluid therapy is given concurrently because of the days, combined with doxycycline ([5-]10 mg/kg q12h PO)
concern for aminoglycoside nephrotoxicity. Furosemide has been recommended. Aminoglycoside precautions for
should not be given during aminoglycoside treatment patient selection and renal function monitoring are as for
because it can exacerbate nephrotoxicity. Therefore amino- dogs (see previous discussion). When the amikacin is dis-
glycoside use is generally contraindicated in patients with continued, oral pradofloxacin (5-10 mg/kg q24[-12]h PO)
CHF or underlying renal disease. can be added. Currently recommended oral therapy for Bar-
It is important to seek confirmation of suspected Barton- tonella infection includes doxycycline (5-10 mg/kg q12h PO;
ella endocarditis infection (see p. 135, discussed earlier) or minocycline at 8.8 mg/kg q12h PO), combined with pra-
because treatment may require extremely long-term antibi- dofloxacin (5-10 mg/kg q24[-12]h PO) for 28 to 42 days (at
otic therapy (e.g., for up to 3 months), using at least two least). Because higher doses and longer treatment duration
antimicrobial drugs with different modes of action, in an generally are needed for treating Bartonella infection, and
attempt to eliminate the organism. Nevertheless, the most because cats are at risk for retinotoxicity when enrofloxacin
effective strategy for eliminating Bartonella in dogs and cats is used at doses >5 mg/kg/day, this agent is no longer recom-
currently remains unproven. In vitro testing and reported mended for Bartonella infections in cats. Jarisch-Herxheimer–
antibiotic minimal inhibitory concentration (MIC) do not like reactions (see previous discussion) also can occur in
reflect efficacy against Bartonella in the host animal. Bacte- cats.
rial persistence can lead to recurrent clinical infection, espe- Supportive care includes management for CHF (see
cially with immunosuppression or concurrent disease Chapter 3) and arrhythmias (see Chapter 4), if present. Com-
process. Although previous recommendations have included plications related to the primary source of infection, embolic
use of azithromycin, this drug is no longer recommended as events, or immune responses are addressed to the extent
first-line therapy for Bartonella because of the rapid develop- possible. Attention to hydration status, nutritional support,
ment of resistance to it. and general nursing care is also important. BP and renal
For dogs with Bartonella endocarditis (or myocardi- function should be monitored, along with other parameters
tis), initial therapy with amikacin (15-30 mg/kg q24h IV, as indicated for the individual patient. Hypertension should
IM, or SC) for 7 to 10 days, combined with doxycycline be vigorously controlled (see Chapter 11). Even when BP
([5-]10 mg/kg q12h PO) has been recommended. Renal is normal, modest additional afterload reduction with an
function must be closely monitored when using an amino- arteriolar vasodilator can help support cardiac function,
glycoside; this agent should not be used in certain patients especially with advancing aortic or mitral valve regurgita-
(see previous discussion). After amikacin is discontinued, tion. Corticosteroids generally are contraindicated. The