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 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)