Effects and safety of iopanoic acid in cats administered levothyroxine

The purpose of this study was to evaluate the safety and effect of iopanoic acid in 13 cats with hyperthyroidism induced by daily subcutaneous administration of 25 μg/kg levothyroxine for a period of 42 days. On day 28 of levothyroxine administration, cats were randomly allocated to receive treatment twice daily with a placebo (control group; n = 4), 50 mg iopanoic acid (low dose group; n = 5), or 100 mg iopanoic acid (high dose group; n = 4) for 14 days. Compared to the control group, T3 concentrations were significantly decreased in both the low dose and high dose groups on days 35 and 42. T3 concentrations in the low dose and high dose groups at days 35 and 42 were not different from day -8. The effect of iopanoic acid on clinical signs of hyperthyroidism was less apparent. Further clinical studies evaluating the long-term effect in cats with spontaneous hyperthyroidism are warranted.