Objective—To determine how rapidly trimethoprimsulfamethoxazole
affects serum total thyroxine (T4)
and thyroid-stimulating hormone (TSH) concentrations
in euthyroid dogs and how quickly hormone
concentrations return to reference values following
discontinuation of administration.
Animals—7 healthy euthyroid dogs.
Procedure—Dogs were given trimethoprim-sulfamethoxazole
(26.5 to 31.3 mg/kg [12 to 14.2 mg/lb],
PO, q 12 h) for a maximum of 6 weeks. A CBC and
Schirmer tear test were performed and serum total T4
and TSH concentrations were measured weekly.
Administration of trimethoprim-sulfamethoxazole
was discontinued if total T4 concentration was less
than the lower reference limit and TSH concentration
was greater than the upper reference limit or if persistent
Results—Six dogs had total T4 concentrations less
than the lower reference limit within 3 weeks; T4
concentration was decreased after 1 week in 3 of
these 6 dogs. In these 6 dogs, TSH concentration
was greater than the upper reference limit within 4
weeks. In 1 dog, T4 and TSH concentrations were
not affected, despite administration of trimethoprimsulfamethoxazole
for 6 weeks. Neutropenia developed
in 4 dogs. In 1 dog, the neutropenia resolved
while trimethoprim-sulfamethoxazole was still being
administered. In the other 3, neutrophil counts
returned to reference values 1 week after drug
administration was discontinued.
Conclusions and Clinical Relevance—Results suggest
that administration of trimethoprim-sulfamethoxazole
at a dosage of 26.5 to 31.3 mg/kg, PO, every 12
hours can substantially alter serum total T4 and TSH
concentrations and neutrophil counts in dogs within
as short a time as a few weeks. (J Am Vet Med Assoc
Objective—To compare the effects of 2 doses of
cosyntropin (5 µg/kg vs 250 µg, IV) on serum concentrations
of cortisol, sex hormones of adrenal origin,
and adrenocortical steroid intermediates and determine
the optimal sample collection time after adrenal
stimulation with cosyntropin.
Procedure—Dogs were randomly assigned to initially
receive cosyntropin at 5 µg/kg or as a total dose of
250 µg, IV. Dogs received the alternate dose 1 to 2
weeks later. Serum was obtained from blood samples
collected before (0 minutes) and 30, 60, 90, and 120
minutes after cosyntropin administration.
Results—Maximum stimulation of cortisol,
androstenedione, progesterone, and 17-hydroxyprogesterone
production was achieved at 60 minutes following
IV administration of cosyntropin at 5 µg/kg or
as a total dose of 250 µg. Serum estradiol concentration
did not increase in response to either cosyntropin
dose. For all hormones, no significant difference in
serum hormone concentrations was found among
sample collection times of 0, 30, 60, and 90 minutes
when comparing the 2 doses of cosyntropin.
Conclusions and Clinical Relevance—Cosyntropin,
when administered at 5 µg/kg, IV, effectively stimulated
maximum production of cortisol, sex hormones of
adrenal origin, and adrenocortical steroid intermediates
at 1 hour after administration. (Am J Vet Res
Objective—To evaluate adrenal sex hormone concentrations
in neutered dogs with hypercortisolemia.
Animals—11 neutered dogs with hypercortisolemia.
Procedure—Serum samples obtained before and 1
hour after administration of ACTH were evaluated for
concentrations of cortisol, progesterone, testosterone,
dehydroepiandrosterone sulfate or androstenedione
or both, and 17-hydroxyprogesterone.
Results—For all dogs, concentrations of 1 or more
adrenal sex hormones were substantially greater than
reference range values before or after administration
of ACTH. Testosterone concentration was not greater
than reference range values in any of the dogs.
Conclusions and Clinical Relevance—Results
emphasize the importance of ruling out hypercortisolemia
before measuring adrenal sex hormone concentrations
as a means of diagnosing adrenal hyperplasia
syndrome (alopecia X) in dogs. (J Am Vet Med Assoc 2001;218:214–216)
Objective—To determine whether the stress of an
ultrasonographic procedure would interfere with the
suppressive effect of dexamethasone during a lowdose
dexamethasone suppression test (LDDST) in
Animals—6 clinically normal adult dogs.
Procedure—In phase 1, an LDDST was performed 5
times at weekly intervals in each dog. Serum samples
were obtained 0, 2, 4, 6, and 8 hours after dexamethasone
injection. A mock 20-minute abdominal ultrasonographic
examination was performed on all dogs at each
time point during the LDDST on weeks 2 through 5. In
phase 2, serum cortisol concentrations were measured
before and immediately after a 20-minute mock
abdominal ultrasonographic examination, as described
for phase 1.
Results—We did not detect significant differences
after dexamethasone injection when comparing
median cortisol concentrations for weeks 2 to 5
(mock ultrasonographic procedure) with median concentration
for week 1 (no mock ultrasonographic procedure).
For 5 of the 6 dogs, cortisol concentrations
after dexamethasone injection decreased to < 35.9
nmol/L after each mock ultrasonographic procedure
and remained low for the duration of the LDDST. In
phase 2, all dogs had significant increases in cortisol
concentrations immediately after the mock ultrasonographic
Conclusions and Clinical Relevance—A 20-minute
mock abdominal ultrasonographic examination performed
during LDDST did not alter results of the
LDDST in most dogs. Cortisol concentrations measured
immediately after a mock ultrasonographic
examination were significantly increased. Ultrasonographic
procedures should be performed a minimum
of 2 hours before collection of samples that will
be used to measure cortisol concentrations. ( Am J Vet Res 2004;65:267–270)
Objective—To determine frequency with which
Staphylococcus schleiferi could be isolated from dogs
with pyoderma and antimicrobial susceptibility patterns
of isolates that were obtained.
Animals—54 dogs with a first (n = 14) or recurrent
(40) episode of pyoderma.
Procedure—Specimens were obtained and submitted
for bacterial culture. Isolates were identified as S
schleiferi on the basis of growth and biochemical
characteristics. Two isolates were submitted for DNA
sequencing to confirm identification. Methicillin susceptibility
was determined by means of disk diffusion
with oxacillin-impregnated disks.
Results—3 of 14 dogs examined because of a first
episode of pyoderma and 12 of 40 dogs examined
because of a recurrent episode of pyoderma were
receiving antimicrobials at the time of specimen collection.
Staphylococcus schleiferi was not isolated
from any dog with first-time pyoderma but was isolated
from 5 dogs with recurrent pyoderma that were
not receiving antimicrobials at the time of specimen
collection and 10 dogs with recurrent pyoderma that
were receiving antimicrobials. Nine isolates were
identified as S schleiferi subsp schleiferi, and 6 were
identified as S schleiferi subsp coagulans. All S
schleiferi subsp schleiferi isolates were resistant to
methicillin, but only 2 S schleiferi subsp coagulans
isolates were. Two methicillin-resistant isolates were
also resistant to fluoroquinolones, and 1 isolate had
intermediate susceptibility to fluoroquinolones.
Conclusions and Clinical Relevance—Results suggest
that S schleiferi subsp schleiferi and S schleiferi
subsp coagulans may be isolated from dogs with recurrent
pyoderma. Although isolates from dogs with pyoderma
were frequently resistant to methicillin, multiple
drug resistance was uncommon. (J Am Vet Med Assoc
Objective—To determine the frequency of isolation and
susceptibility patterns of Staphylococcus schleiferi from
healthy dogs and dogs with otitis, pyoderma, or both
that had or had not received antimicrobial treatment.
Procedure—Dogs were allocated to 1 of 4 groups:
healthy dogs (n = 13), dogs without otitis but with pyoderma
(10), dogs with otitis but without pyoderma (11),
and dogs with otitis and pyoderma (16). Bacteriologic
culture of ear swab specimens was performed in all
dogs. Bacteriologic culture of skin swab specimens
was also performed in dogs with concurrent pyoderma.
Isolates were identified as S schleiferi subsp schleiferi
or S schleiferi subsp coagulanson the basis of growth
and biochemical characteristics.
Results—S schleiferi was not isolated from any dogs with
pyoderma only. Staphylococcus schleiferi subsp schleiferi
was isolated from the ears of 2 healthy dogs, and the skin
and ears of 2 dogs and the skin of 1 dog with otitis and
pyoderma. Staphylococcus schleiferi subsp coagulans
was isolated from the ears of 3 dogs with otitis only, and
the ears of 6 dogs and the skin of 2 dogs with otitis and
pyoderma. One of the S schleiferi subsp schleiferi isolates
from ears, 2 of the S schleiferi subsp coagulansisolates
from ears, and 1 of the S schleiferi subsp coagulansisolates
from the skin were resistant to methicillin. One
methicillin-resistant isolate from the ears and 1 from the
skin were also resistant to fluoroquinolones.
Conclusions and Clinical Relevance—S schleiferi
subsp schleiferiwas detected in healthy dogs and dogs
with otitis and pyoderma. Methicillin-resistant and -susceptible
S schleiferi subsp schleiferi and S schleiferi
subsp coagulans were detected as the predominant
organisms in dogs with otitis. ( J Am Vet Med Assoc 2005;227:928–931)
Objective—To determine whether resistance to oxacillin and other antimicrobials in 3 Staphylococcus spp commonly isolated from dogs increased from 2001 to 2005.
Design—Retrospective case series.
Sample Population—1,772 clinical samples of various types obtained from dogs examined at the University of Tennessee Veterinary Teaching Hospital or at regional veterinary hospitals and submitted to the bacteriology and mycology laboratories associated with the teaching hospital.
Procedures—Samples were submitted by attending veterinarians to the bacteriology and mycology laboratories for routine aerobic microbial culture. Identification and antimicrobial susceptibility procedures were performed on all isolates. Susceptibility reports for each antimicrobial and Staphylococcus spp were determined from aggregate electronically archived test results. Oxacillin and multidrug resistance for Staphylococcus intermedius was analyzed by reviewing disk diffusion zone measurements.
Results—Oxacillin resistance increased among S intermedius isolates during the past 5 years, and the increase was associated with multidrug resistance. In 2005, 1 in 5 Staphylococcus spp isolates from canine clinical samples was resistant to oxacillin. The most common staphylococcal species isolated were S intermedius (n = 37), Staphylococcus schleiferi (21), and Staphylococcus aureus (4), and frequencies of oxacillin resistance in isolates of these species were 15.6%, 46.6%, and 23.5%, respectively.
Conclusions and Clinical Relevance—Veterinarians should be aware of the potential for empiric drug treatment failures in instances where Staphylococcus spp infections are common (eg, pyoderma). Judicious use of bacterial culture and susceptibility testing is recommended.
Objective—To evaluate effects of trimethoprim-sulfamethoxazole
(T/SMX) on thyroid function in dogs.
Animals—6 healthy euthyroid dogs.
Procedure—Dogs were administered T/SMX (14.1 to
16 mg/kg, PO, q 12 h) for 3 weeks. Blood was collected
weekly for 6 weeks for determination of total
thyroxine (TT4), free thyroxine (fT4), and canine thyroid-
stimulating hormone (cTSH) concentrations.
Schirmer tear tests were performed weekly. Blood
was collected for CBC prior to antimicrobial treatment
and at 3 and 6 weeks.
Results—5 dogs had serum TT4 concentrations
equal to or less than the lower reference limit, and 4
dogs had serum fT4 less than the lower reference
limit after 3 weeks of T/SMX administration; cTSH
concentrations were greater than the upper reference
limit in 4 dogs. All dogs had TT4 and fT4 concentrations
greater than the lower reference limit
after T/SMX administration was discontinued for 1
week, and cTSH concentrations were less than reference
range after T/SMX administration was discontinued
for 2 weeks. Two dogs developed
decreased tear production, which returned to normal
after discontinuing administration.
Conclusions and Clinical Relevance—Results suggest
that administration of T/SMX at a dosage of 14.1 to
16 mg/kg, PO, every 12 hours for 3 weeks caused
decreased TT4 and fT4 concentrations and increased
cTSH concentration, conditions that would be compatible
with a diagnosis of hypothyroidism. Therefore, dogs
should not have thyroid function evaluated while receiving
this dosage of T/SMX for > 2 weeks. These results
are in contrast to those of a previous study of trimethoprim-
sulfadiazine. (Am J Vet Res 2005;66:256–259)
Objective—To determine the methicillin-resistant
profile of staphylococcal isolates from the skin of
dogs with pyoderma.
Animals—90 dogs with pyoderma.
Procedure—Staphylococci isolated from dogs with
pyoderma were tested for susceptibility to methicillin
by use of a standard disk diffusion test with oxacillin
disks. The DNA extracted from the isolates was tested
for the mecA gene that encodes the penicillinbinding
protein 2a (PBP2a) by use of a polymerase
chain reaction (PCR) assay. The expression of PBP2a
was determined with a commercial latex agglutination
assay. Species of staphylococcal isolates were
identified by use of morphologic, biochemical, and
Results—Most of the isolated staphylococci were
Staphylococcus intermedius isolates. Whereas only 2
of 57 S intermedius isolates were resistant to methicillin,
approximately half of the isolates had the mecA
gene and produced PBP2a. Staphylococcus schleiferi
was the second most common isolate. Widespread
resistance to methicillin was found among S schleiferi
isolates. More coagulase-negative S schleiferi isolates
were identified with mecA gene-mediated resistance
to methicillin, compared with coagulase-positive S
Conclusions and Clinical Relevance—The latex
agglutination assay for the detection of PBP2a
expression coupled with the PCR assay for the mecA
gene may provide new information about emerging
antimicrobial resistance among staphylococcal isolates.
(Am J Vet Res2004;65:1265–1268)