Ipodate treatment of hyperthyroidism in cats.

OBJECTIVE

To evaluate the efficacy and safety of ipodate in the treatment of hyperthyroidism in cats.

DESIGN

Prospective case series.

ANIMALS

12 cats with hyperthyroidism treated at The Animal Medical Center between November 1994 and March 1996.

PROCEDURE

Each cat initially received 100 mg of ipodate/d, PO. The drug's effects on clinical signs, body weight, heart rate, and serum triiodothyronine (T3) and thyroxine concentrations were evaluated 2, 4, 6, 10, and 14 weeks after initiation of treatment. A CBC and serum biochemical analyses were performed at each evaluation to monitor potential adverse effects of the drug. Dosage of ipodate was increased to 150 mg/d and then to 200 mg/d at 2-week intervals if a good clinical response was not observed.

RESULTS

8 cats responded to treatment and 4 did not. Among cats that responded, mean body weight increased and mean heart rate and serum T3 concentration decreased during the study period. Among cats that did not respond, mean body weight decreased and mean heart rate and serum T3 concentration were not significantly changed. Serum thyroxine concentration remained high in all cats. Adverse clinical signs or hematologic abnormalities attributable to ipodate treatment were not reported in any of the cats.

CLINICAL IMPLICATIONS

Ipodate may be a feasible alternative to methimazole for medical treatment of hyperthyroidism in cats, particularly those that cannot tolerate methimazole and are not candidates for surgery or radiotherapy. Cats with severe hyperthyroidism are less likely to respond to ipodate than are cats with mild or moderate disease, and cats in which serum T3 concentration does not return to the reference range are unlikely to have an adequate improvement in clinical signs.