Effects of deracoxib and aspirin on serum concentrations of thyroxine, 3,5,3'-triiodothyronine, free thyroxine, and thyroid-stimulating hormone in healthy dogs.
OBJECTIVE
To evaluate the effects of deracoxib and aspirin on serum concentrations of thyroxine (T4), 3,5,3'-triiodothyronine (T3), free thyroxine (fT4), and thyroid-stimulating hormone (TSH) in healthy dogs.


METHODS
24 dogs.


METHODS
Dogs were allocated to 1 of 3 groups of 8 dogs each. Dogs received the vehicle used for deracoxib tablets (PO, q 8 h; placebo), aspirin (23 to 25 mg/kg, PO, q 8 h), or deracoxib (1.25 to 1.8 mg/kg, PO, q 24 h) and placebo (PO, q 8 h) for 28 days. Measurement of serum concentrations of T4, T3, fT4, and TSH were performed 7 days before treatment (day -7), on days 14 and 28 of treatment, and 14 days after treatment was discontinued. Plasma total protein, albumin, and globulin concentrations were measured on days -7 and 28.


RESULTS
Mean serum T4, fT4, and T3 concentrations decreased significantly from baseline on days 14 and 28 of treatment in dogs receiving aspirin, compared with those receiving placebo. Mean plasma total protein, albumin, and globulin concentrations on day 28 decreased significantly in dogs receiving aspirin, compared with those receiving placebo. Fourteen days after administration of aspirin was stopped, differences in hormone concentrations were no longer significant. Differences in serum TSH or the free fraction of T4 were not detected at any time. No significant difference in any of the analytes was detected at any time in dogs treated with deracoxib.


CONCLUSIONS
Aspirin had substantial suppressive effects on thyroid hormone concentrations in dogs. Treatment with high dosages of aspirin, but not deracoxib, should be discontinued prior to evaluation of thyroid function.
Department of Small Animal Clinical Sciences, Virginia-Maryland Regional College of Veterinary Medicine, Blacksburg, VA 24061-0442, USA.
David L
DL
Panciera
Kent R
KR
Refsal
Kathleen A
KA
Sennello
Daniel L
DL
Ward
D000284:Administration, Oral; D000818:Animals; D001241:Aspirin / Q000008:administration & dosage / Q000494:pharmacology*; D004285:Dogs / Q000097:blood*; D005260:Female; D008297:Male; D010919:Placebos; D012016:Reference Values; D012709:Serum Albumin / Q000187:drug effects / Q000378:metabolism; D012712:Serum Globulins / Q000187:drug effects / Q000378:metabolism; D013449:Sulfonamides / Q000008:administration & dosage / Q000494:pharmacology*; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000097:blood*; D014284:Triiodothyronine / Q000097:blood*; D000096926:Benzenesulfonamides
D001241:Aspirin; D010919:Placebos; D012709:Serum Albumin; D012712:Serum Globulins; D013449:Sulfonamides; D013972:Thyrotropin; D013974:Thyroxine; D014284:Triiodothyronine; C471996:deracoxib; D000096926:Benzenesulfonamides