Hill’s Updates Guidelines For Y/d Feline


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After the launch of its Prescription Diet y/d Feline Thyroid Health pet food last year, Hill’s Pet Nutrition Inc. of Topeka, Kan., has released an updated set of guidelines and algorithms to assist veterinary care providers who are managing hyperthyroid patients with the food.

Hyperthyroidism is one of the most common diseases in middle-aged and older cats. Resulting from too-high levels of thyroid hormone (T4) and increased metabolism, the illness can cause a range of clinical findings, from hypertension to ravenous appetite, weight loss and excessive urination. Some cats also have concurrent kidney disease.

Traditional treatment options have included radioactive iodine, the medication methimazole to control levels of thyroid hormone, or a thyroidectomy.

A decade in the making, Prescription Diet y/d Feline gives veterinarians a new management tool—and so far, says David Bruyette, DVM, Dipl. ACVIM, medical director of VCA West Los Angeles Animal Hospital, it has been working. 

Since June, Dr. Bruyette and his veterinary health care team have been using the therapeutic cat food to manage newly diagnosed feline hyperthyroid patients and those previously diagnosed that are transitioning from anti-thyroid medication.

“What we’ve seen is that in the 22 cats we’ve managed to date that have been eating the pet food, 19 have come back to normal and three didn’t,” he reports. “In those three cats, two were eating food other than the y/d; they were getting into another cat’s food or getting treats. The other cat didn’t respond as expected and we were not able to identify a reason.”

Prescription Diet y/d Feline must be the only food eaten by the patient. Any other food or treats will decrease or prevent the cat food’s beneficial effects.

Hill’s reports that the limited-iodine food has proven to be 90 percent effective, and Bruyette reports similar findings in his clinical patients.

“We’ve seen about 86 percent effectiveness,” he says. “We need to continue managing more cats, but so far it appears like the pet food is highly effective in getting their thyroid levels down into the normal range and controlling the signs of hyperthyroidism.”

Diagnostics First

S. Dru Forrester, DVM, MS, Dipl. ACVIM,  director of scientific and technical communication for Hill’s, helped develop the new guidelines and algorithms for managing feline hyperthyroid patients with y/d Feline. She says practitioners should first consider a patient’s clinical presentation, which may include signs such as weight loss, polyphagia, hyperactivity, polyuria, polydipsia, cardiac murmur, tachycardia, vomiting and diarrhea.

Clinical examination should be followed with a diagnostic evaluation, Dr. Forrester says, which includes the patient’s history, physical examination, complete blood count, serum chemistries, urinalysis and measurement of serum thyroxine, or T4.

“When doing the physical examination, veterinarians always want to palpate the area in the neck where the thyroid is located, which is just below the larynx,” Dr. Forrester says. “It takes some skill to find it, but they should be able to feel a palpable nodule or mass, which is almost always a benign tumor.

“With most cats, you can diagnose hyperthyroidism based on the T4 levels,” she says. “If not, it can get a little tricky. If you suspect the cat is hyperthyroid but the T4 is not abnormal, you can wait and repeat it a few weeks later.”

Management Options

With a diagnosis determined, practitioners should discuss their findings with the clients and outline the various management options, Forrester says. They include radioactive iodine, the anti-thyroid medication methimazole to control the levels of thyroid hormone, nutritional management using Hill’s Prescription Diet y/d Feline, or a thyroidectomy.

“Every veterinarian who diagnoses this should discuss all of those options with the pet owner, and the advantages and disadvantages of each,” Forrester advises, noting that different situations will require different solutions.

Some owners, for instance, may not be able to administer a pill. Others may not have a radioactive iodine treatment center available or be able to afford its upfront costs, she says. And still others may have a multi-cat household, which means the hyperthyroid cat could get into the other cat’s food.

“You have to figure out what’s best for the individual cat and the owner,” Forrester says.  

Making a Transition

Some owners of feline hyperthyroid patients already being treated with medication may be candidates to switch to nutritional management, Forrester says.

“Some folks have difficulty giving medications, which are needed every day for the rest of the cat’s life,” she says. “And the medication has some potential side effects that could be significant. So if the cat is experiencing problems with medication or can’t be medicated appropriately by the owner, that’s  a great candidate for transitioning.”

If, however, a difficult-to-regulate or critically ill patient is doing well on medication, “Then it’s reasonable to leave that cat alone and not change its medical management just because there’s a new pet food,” Forrester says.

When a hyperthyroid cat is being transitioned from drugs to the food, Forrester emphasizes that a baseline evaluation should be done. Depending on the results, the medication dosage is either discontinued or reduced by 50 percent as soon as the transition to the cat food begins.

“The food and the medication can have a potentially potent effect, making the thyroid hormone go too low,” Forrester says. “Cats should be carefully monitored when they transition off the medication and are beginning nutritional management. In the recently revised guidelines, we added more detailed information to help veterinarians understand the importance of doing that baseline evaluation, even though the cat is receiving anti-thyroid medication.”

The most current version of suggested guidelines and algorithms are available online.

Choose Cases Wisely

For practitioners who are new to using nutritional management of cats with hyperthyroidism, Forrester recommends starting with some straightforward cases first. “I wouldn’t pick a critical cat as my first case,” she says.

Whether managing a newly diagnosed patient or one that’s transitioning from medication to food, veterinarians should carefully monitor the cat. Initial rechecks should include physical examination and measuringT4, BUN, serum creatinine and urine specific gravity; long-term evaluation is indicated every 6 months and could be done at the time of routine wellness examinations.

“The key is careful monitoring,” Forrester says. “Use your clinical judgment. The guidelines we’ve provided are suggestions and can’t account for every nuance of every single patient. The attending  veterinarian is in the best position to make decisions for their individual patients.”

For individual patient recommendations, health care team members can call the Hill’s Veterinary Consultation Service at 800-548-8387.

This Education Series article was underwritten by Hill’s Pet Nutrition of Topeka, Kan.

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