Complete Care for Your Aging Cat - Amy Shojai [106]
If both thyroid lobes are surgically removed, Dr. Schulman says most cats do very well and bounce back pretty quickly. Interestingly, although a few need thyroid supplements, most do not need further medication at all.
Medical Treatment
“The drug methimazole (Tapazole) is the most common medical management for hyperthyroidism,” says Steven L. Marks, BVSc, an internist and surgeon at North Carolina State University. Depending on its severity and the size of the cat, the dose ranges from about 2.5 to 7.5 milligrams twice a day. The drug only suppresses the thyroid hormone production, so it must be given every day for the rest of the cat’s life. However, many cats can be treated with 2.5–5 mg once daily or every other day if side effects occur. Some cats are given Tapazole on a temporary basis until other treatment can be scheduled.
Dr. Hager warns that up to a fifth of the cats treated with Tapazole will have an adverse reaction. “They become terribly ill with problems with their liver. It can affect their blood, cause itchy face. They can have lots of problems,” he says. Also, because the drug is not a cure and little adenomas continue to grow, he says the cat needs more and more Tapazole as time goes one.
“Kitties have an aversion to being pilled,” he cautions, which can interfere with the bond you share with your pet. Repeated unpleasant associations with medicating can cause the cat to hide when he sees you. Another option is transdermal application of the medicine. Tapazole is compounded into a cream or gel that is able to carry the medicine through the skin when smeared on the inside of the ear.
Tapazol, a human drug, has been successfully used off-label for hyperthyroid cats more than thirty years. In 2009, The U.S. Food and Drug Administration announced approval of Dechra Veterinary Product's Felimazole (methimazole) specifically for treatment of hyperthyroidism in cats with coated tablets in 2.5 to 5 mg dosages. However, in a Veterinary Information Network report, Margie Scherk, DVM, DABVP (Feline) notes the new drug is identical to the methimazole already in use. However, in Great Britain (and some states in the US), veterinarians must use available licensed drugs over generics, so this likely will make a difference for some cats and their owners.
Dr. Scherk and others would like the FDA to investigate carbimazole that is converted to methimazole after metabolism. This common oral treatment for feline hyperthyroidism is sold as Vidalta in the UK by Intervet (part of Schering Plough Animal Health).
Transdermal medication has been successfully used for years in human medicine, and has been used for some time in veterinary medicine especially for pain control (fentanyl patches) and in hyperthyroid cats. Research by Dr. Marks and others looks at the benefits of transdermal application of several products, including methimazole in cats. “Pets don’t like to receive pills if they don’t have to,” says Dr. Marks. The struggle and stress of medicating cats can make them even sicker, so ask your veterinarian about less stressful medication options. More transdermal medications should become available when results of these studies are published.
When a hyperthyroid cat has other health concerns, those may also require medical treatment. For instance, Dr. Little says that hypertension is very common but highly manageable with the proper medication. “The most commonly used one is Norvasc (amlodipine). It’s a human heart drug but it’s the best drug for hypertension in cats.” She says controlling high blood pressure makes a clear difference to their quality of life day to day.
Radioactive Iodine
The third option for feline hyperthyroidism is radioactive iodine treatment, I-131. “That’s a one time only deal, but it has limited availability, typically in veterinary universities,” says Dr. Schulman. A commercial enterprise, called Radiocat, has established