Transdermal Methimazole for Felines

Tired of scratches, hunting for, wrestling, and cleaning up after your kitty every time you give her thyroid medication? If kitty does not like taking pills and suspensions she is not alone. You might be happy to learn there is an easier way!! Her hyperthyroid medication, methimazole, can be compounded into a topical preparation by Pharmacy Solutions and applied to the skin in her ear. This makes medication time much more pleasant for both owner and kitty!!

The oral administration of anti-thyroid medications is frequently used as treatment of hyperthyroidism in felines, however, due to many cats temperament the oral administration of tablets and suspensions can sometimes prove difficult. Thanks to a study performed by Sartor et al. at the University of Wisconsin-Madison School of Veterinary Medicine, it was determined that transdermal methimazole was as safe and effective as oral methimazole in the control of hyperthyroidism in cats. In this study, 47 felines with newly diagnosed hyperthyroidism were randomized to receive either transdermal methimazole (27 cats) in PLO gel to the inner pinna or oral methimazole (17 cats) at 2.5mg every 12 hours for both routes. The cats were evaluated at weeks 0, 2, and 4 with a physical exam, body weight determination, CBC, urinalysis, measurement of total levothyroxine (T4) concentration, and completion of owner questionnaire.  At 2 weeks, significantly more cats treated wit oral methimazole had serum T4 concentrations within the reference range (14 to 16 cats) compared to those treated transdermally (14 of 25; p=0.027). However, this difference was no longer significant at 4 weeks of treatment (9 of 11 for oral vs. 14 of 21 for transdermal). Additionally, cats treated with oral methimazole had higher incidence of gastrointestinal (GI) adverse effects (4 of 17 cats) compared to cats treated with transdermal methimazole (1 of 27; p=0.04), but no differences were found between the groups in the incidence of neutropenia, hepatotoxicity, or facial excoriations.  With its ease of administration, efficacy, and lack of GI adverse effects, transdermal methimazole is an attractive choice for many cat owners suffering from hyperthyroidism. ¹

Feline Dosing: 2.5mg to 5mg topically to hairless inner ear pinna every 12 hours

1. Sartor LL, Trepanier LA, Kroll MM, Rodan I, Challoner L. Efficacy and safety of transdermal methimazole in the treatment of cats with hyperthyroidism. J Vet Intern Med. 2004; 18: 65-655.