Results indicate that serum total T4, free T4, and total T3 concentrations may be low (ie, in the hypothyroid range) in dogs with moderate to severe nonthyroidal disease. Serum TSH concentrations are more likely to remain within the reference range in sick dogs.

The effect of daily doses of 5-15 mg of methimazole on the platelet count, prothrombin time (PT), activated partial thromboplastin time (APTT), and proteins induced by vitamin K absence or antagonists (PIVKA) clotting time in 20 hyperthyroid cats was determined. No significant (P > .05) difference was found in median platelet count. PT, APTT, or PIVKA clotting time before treatment compared to median values at 2-6 weeks or > or =7-12 weeks of methimazole treatment. No cat had a prolonged APTT at any time. At 2-6 weeks of methimazole treatment, 1 cat each developed thrombocytopenia or prolonged PIVKA clotting time despite initially normal values. Three cats had abnormal coagulation tests (prolonged PT [n = 1] and PIVKA clotting time [n = 3]) before treatment that fluctuated during treatment. Excluding the 3 cats that had abnormal PIVKA clotting time before treatment, prolonged PIVKA clotting time developed in 6% (1/17; 95% confidence interval, 0-28%) cats treated with methimazole for 2-6 weeks. Seemingly. doses of methimazole commonly used to treat hyperthyroidism in cats do not cause alteration in PT and APTT, and only rarely prolong PIVKA clotting time. Nevertheless, abnormal PIVKA clotting time may explain bleeding tendencies unassociated with thrombocytopenia in methimazole-treated hyperthyroid cats.

No abstract

The effect of daily doses of 5-15 mg of methimazole on the platelet count, prothrombin time (PT), activated partial thromboplastin time (APTT), and proteins induced by vitamin K absence or antagonists (PIVKA) clotting time in 20 hyperthyroid cats was determined. No significant (P Ͼ .05) difference was found in median platelet count, PT, APTT, or PIVKA clotting time before treatment compared to median values at 2-6 weeks or Ն7-12 weeks of methimazole treatment. No cat had a prolonged APTT at any time. At 2-6 weeks of methimazole treatment, 1 cat each developed thrombocytopenia or prolonged PIVKA clotting time despite initially normal values. Three cats had abnormal coagulation tests (prolonged PT [n ϭ 1] and PIVKA clotting time [n ϭ 3]) before treatment that fluctuated during treatment. Excluding the 3 cats that had abnormal PIVKA clotting time before treatment, prolonged PIVKA clotting time developed in 6% (1/17; 95% confidence interval, 0-28%) cats treated with methimazole for 2-6 weeks. Seemingly, doses of methimazole commonly used to treat hyperthyroidism in cats do not cause alteration in PT and APTT, and only rarely prolong PIVKA clotting time. Nevertheless, abnormal PIVKA clotting time may explain bleeding tendencies unassociated with thrombocytopenia in methimazole-treated hyperthyroid cats.Key words: Coagulation; Drug therapy; Feline; Hyperthyroidism.F eline hyperthyroidism resulting from functional thyroid adenomatous hyperplasia (or adenoma) is 1 of the most commonly diagnosed disorders in small animal practice.1 Treatment of the hyperthyroid state is designed to reduce the excessive production of thyroid hormone from adenomatous thyroid tissue by either surgical thyroidectomy, radioactive iodine ( 131 I), or chronic administration of an antithyroid drug.1 Many considerations (eg, financial constraints, surgical and anesthetic risks, pet quarantine for radiation therapy) favor election by the owners of antithyroid drug treatment as either short-term preoperative or permanent management.The most commonly used antithyroid drug, methimazole, a is actively concentrated in the thyroid gland, where it acts to inhibit the synthesis of thyroid hormones.2,3 Although relatively safe when administered to hyperthyroid cats, methimazole occasionally causes serious adverse effects. The adverse effects usually develop within the 1st 2-3 months of treatment and include hepatopathy, thrombocytopenia, and agranulocytosis.1,2 Bleeding tendencies (epistaxis, oral hemorrhage, excessive hemorrhage during surgery) occur in methimazole-treated cats, and are generally attributed to thrombocytopenia.2 Bleeding tendencies unassociated with thrombocytopenia have been encountered rarely in methimazole-treated hyperthyroid cats by us and others. 2,4From the Departments of Clinical Sciences (Randolph, DeMarco, Center) and Population Medicine and Diagnostic Sciences (Scarlett, Brooks), College of Veterinary Medicine, Cornell University, Ithaca, NY; and the Oradell Animal Hospital Inc (Kantrowitz, Crawford), Oradell, NJ. Dr DeMarc...