If you have a cat with thyroid disease, you're far from alone. Hyperthyroidism, or an overactive thyroid gland, is the most common hormone disorder in older cats, according to the veterinarian David Bruyette. Speaking at a 2008 CVC conference for veterinarians, Dr. Bruyette listed the most common symptoms of hyperthyroidism in cats: weight loss despite a ravenous appetite, excessive drinking and urination, vomiting, vocalisation or howling, especially at night, and increased energy and activity. Untreated hyperthyroidism in cats can take a toll on the heart and kidneys. But the disease can be managed with medication.
Methimazole (brand names, Tapazole and Felimazole) is the drug used most often to treat hyperthyroid cats, says veterinarian Wendy Brooks on the website VeterinaryPartner.com. Dr. Brooks advises giving the medication twice a day for the rest of the cat's life. For cats who are difficult to pill, methimazole can be compounded into a flavoured liquid, soft moist treats or a transdermal gel to rub inside an ear tip. Possible side effects of methimazole include scratching around the ears, lethargy, loss of appetite and vomiting. The drug can also cause liver toxicity and changes in the bone marrow, according to Dr. Brooks. Starting at a low dose and working up to a therapeutic level reduces the likelihood of side effects.
Carbimazole is converted to methimazole in the cat's body and is less likely to cause side effects, says Dr. Bruyette. It, too, must be given twice a day for life. Carbimazole is not sold commercially in the United States, but it's available from compounding pharmacies.
Vidalta is carbimazole formulated for controlled release and is given just once a day. As of 2010, Vidalta was sold only in the United Kingdom and Europe. But veterinarian Thomas K. Graves expects it will be available in the United States in the future.
Some hyperthyroid cats remain well regulated on natrum muriaticum, a homeopathic remedy. Speaking at a World Small Animal Veterinary Congress, veterinarian Peter Dobias described successful treatment of hyperthyroid cats using natrum muriaticum but cautioned that "treatment should only be performed by a veterinarian who has deep knowledge of the principles of classical homeopathy."
One injection of radio iodine cures almost all treated cats, the veterinarians at Southpaws Veterinary Specialists and Emergency Center in northern Virginia say. The treatment is done in a special facility, usually a veterinary referral hospital, and the cat must stay at the facility until the amount of radiation it releases reaches safe levels. Although the length of time varies, this usually takes two to three days. A small number of cats--less than 5 per cent--become hypothyroid after treatment and need a daily thyroid hormone.
Thyroxine (generic name, levothyroxine) is the thyroid hormone supplement used to treat hypothyroidism, or an underactive thyroid gland, in cats. Like other thyroid medications, it can be compounded into a flavoured liquid, soft moist treats or a transdermal gel. Hypothyroidism is rare in cats and most commonly occurs in cats who have been treated for hyperthyroidism with surgery or radioactive iodine, according to veterinarian and PetPlace.com contributor Rhea Morgan.