Felanorm® (methimazole) Oral Solution is now FDA approved
Hyperthyroidism, the overproduction of thyroid hormone by the thyroid glands, is one of the most commonly diagnosed endocrine diseases in cats. It’s estimated that 10% of cats over 10 years of age have this condition. While typically identified in older cats, it isn’t limited to this group.
Some of the more common symptoms associated with this disease include weight loss, increased appetite, diarrhea, vomiting, poor hair coat and behavioral changes such as hyperactivity, irritability or aggression. Less obvious to the cat owner initially are secondary signs such as hypertension (high blood pressure) and increased drinking and urination (often associated with decreased kidney function) that are commonly found with progression of the disease. These latter signs are often detected through a thorough physical examination coupled with blood and urine evaluation by a veterinarian.
Hyperthyroidism results from a functional tumor in one or both of the thyroid glands, which are located in the neck along the trachea (windpipe). The vast majority of these tumors are benign (adenomas), although malignant versions (adenocarcinomas) do occur in about 1–3% of diagnosed cases. Left untreated, hyperthyroidism can lead to life-threatening problems for the cat. However, if adequately treated and regularly monitored, most cats with hyperthyroidism can enjoy a significantly improved quality of life and life expectancy. There are currently four options to treat this condition, all of which have pros and cons and the potential for side effects.
1. Radioactive iodine therapy
In this treatment method, radioactive iodine is administered intravenously to the cat. Because the thyroid glands selectively concentrate the radioactive iodine, the thyroid tumor is exposed to levels of radiation that can, in most cases, eliminate the tumor.This treatment is considered the “gold standard” because it has the potential to cure the disease. It also has the advantage of addressing any functional thyroid tissue that is not located in the “normal” expected location.
The downside of this therapy is that it can be costly, and many areas of the country do not have convenient access to facilities capable of administering the radioactive iodine. Because of the dangers of radiation, these cats often need to be held in a facility equipped to manage radiation exposure during treatment and require special handling for a period of time once they’ve been discharged in order to minimize human exposure.
2. Surgery
In some cases, it’s possible to surgically remove one or both affected thyroid glands containing a tumor. Because this is a disease that can affect both thyroid glands, these patients may require subsequent surgery if only one gland is removed and another tumor is identified at a later date.In ideal cases, successful surgery can potentially eliminate the disease, thereby eliminating the need for daily medication. One consideration when evaluating this option is that there is the potential to damage the parathyroid gland(s) or nerves or blood vessels that are found in and associated with the thyroid glands. This can lead to complications that may themselves necessitate chronic treatment. Additionally, hyperthyroid cats may have increased risk of the anesthetic procedure as a result of the effects of increased thyroid hormone on their system.
3. Dietary restriction of iodine
Hill’s Pet Nutrition markets a diet (Hill’s Prescription Diet® Thyroid Care y/d®) that’s restricted in iodine content. Because the only source of iodine in a cat’s system is through dietary absorption, and because the production of thyroid hormone depends on the availability of iodine, if the iodine intake is appropriately restricted, the circulating thyroid hormone level is reduced.The primary drawbacks associated with this diet are related to acceptance of the food and the necessity of avoiding most treats, top dressings, and food variety that many cats crave, for the rest of their life.
4. Medical management
By far, the most commonly employed therapy for this disease is the use of “antithyroid” medication. Methimazole, the only drug approved for the treatment of hyperthyroidism in cats in the U.S., decreases the production of thyroid hormone by the thyroid gland. This drug causes the cat’s thyroid level to fall within the normal range, often reversing many of the signs commonly seen with this disease. This treatment does not “cure” the cat but can generally be used successfully for long-term management.The downside to this method of management is that it is lifelong, and usually involves once or twice daily administration of oral medication. Transdermal (absorbed across the skin) preparations of the antithyroid drug are sometimes prescribed in situations where oral administration is “challenging.”
Unfortunately, transdermal drugs are often not consistently or reliably absorbed across the skin of cats and can leave the family and other household pets potentially exposed to the drug through petting and grooming.
Norbrook is pleased to have been the first pharmaceutical manufacturer to launch a veterinary approved methimazole oral solution to the U.K. in 2016. Compared to the current oral tablets on the market, Norbrook’s liquid formulation makes it easier to accommodate fine dose adjustments and is less stressful to administer for both the cat and its caretaker. The oral solution is easily administered to most cats and its low-volume liquid formulation helps to avoid the struggle of trying to force a cat to take daily pills.
Available and widely accepted in the U.K., EU and Australia, Norbrook’s methimazole oral solution has a successful track record of making the medical management of feline hyperthyroidism much less of a struggle for cats and their owners. With Felanorm® (methimazole) Oral Solution now FDA approved for the United States, veterinarians and cat owners alike will have an additional medical option for managing this disease in cats.
References
1. Peterson M. Hyperthyroidism in cats: what’s causing this epidemic of thyroid disease and can we prevent it? J Feline Med Surg. 2012 Nov;14(11):804-818. doi: 10.1177/1098612X12464462. PMID: 230870062. Naan EC, Kirpensteijn J, Kooistra HS, Peeters ME. Results of thyroidectomy in 101 cats with hyperthyroidism. Vet Surg. 2006;35:287-293.