Veterinary Information: Feline HyperthyroidismPage 5 (5)Continue Treatment of Feline Hyperthyroidism: 3.)Anti-Thyroid Drug Therapy: Methimazole is a drug that blocks the thyroid hormone synthesis and therefore lowers serum levels of thyroid hormones. It is both a good short-term pre-operative as long term treatment option. It is without the surgical risks of thyroidectomy and no special facilities are needed for radioactive iodine treatment. It therefore offers a good alternative for the two curative treatment options, also for very old cats or cats with concurrent diseases. Intial Methimazole dose is 5-15 mg/day. T4 levels should be monitored with a 2-3 week interval for the first 3 months: 1.)Low T4: Decrease dosage by 2.5-5 mg/day; 2.)High T4: Increase dosage by 2.5-5 mg/day Side-effects usually occur during the first 3 months of treatment: vomiting, anorexia, severe depression, (haemolytic anemia and hemorrhagic diathesis are less common). After the first 3 months the T4 screening interval can be changed to 1x/6months. Prognosis: The prognosis is dependant on the stage of hyperthyroidism, concurrent diseases and the choice of treatment. It should be emphasized that surgical thyroidectomy and radioactive iodine treatment are the only curative treatment options. Anti-thyroid drugs do not inhibit the tumor growth.
A.V. van Marrewijk, DVM Literature: Ettinger SJ, Feldman EC, Peterson ME, Textbook of Veterinary Internal Medicine, WB Saunders Company, Philadelphia (2000) 5th edition: 1400-1415 Return from Feline Hyperthyroidism to the Vet Info Database...
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