Are all hyperthyroid cats good candidates for 131I therapy?
To be candidates for 131I therapy, screening lab work (CBC, chem panel, T4 and if possible, a urinalysis) must be performed by the referring veterinarian within 60 days of the treatment date and the results faxed or e-mailed to me. Since hyperthyroidism can mask pre-existing kidney disease (the elevated blood pressure and cardiac output of hyperthyroidism can artificially normalize kidney tests in these cats), it is sometimes necessary for cats to complete a “Tapazole trial” before undergoing 131I therapy. For the Tapazole trial, the cat takes methimazole or Tapazole for 3 weeks. After normalization of thyroid levels with the antithyroid medication and while still taking the methimazole or Tapazole, blood tests (CBC, chem panel and T4) are performed by the referring veterinarian to evaluate the adequacy of the cat’s kidney function. If no dramatic worsening of kidney function is detected in the “Tapazole trial”, then the cat is considered a good candidate for 131I therapy. A “Tapazole
