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Our Thyroid group of Pet Care products contains a drug for treating hyperthyroidism, which is overactive thyroid in cats and dogs.

Use the search feature to quickly find the product you are looking for by entering either the active ingredient, e.g. carbimazole; or the product name e.g. Neo-Mercazole.

The thyroid and thyroid hormone

The thyroid gland consists of 2 small lobes situated in the neck around the trachea (windpipe). 

The thyroid gland produces two hormones; calcitonin, which regulates calcium metabolism and thyroid hormone, which controls many important body functions, including how the body uses energy, regulates temperature, metabolises nutrients, and controls growth and development. 

Thyroid hormone exists in two forms.  Thyroxine or levothyroxine, also known as T4 and liothyronine or L-triiodothyronine also known as T3.  Up to 90% of thyroid hormone secreted by the thyroid gland is T4, which is inactive but is converted to the active form of thyroid hormone T3 when it reaches its target tissue. This conversion takes place in the liver, kidney and other tissues of the body and T3 then interacts with a specific receptor inside the nucleus of cells, to influence the transcription of specific pieces of DNA (genes) to produce proteins needed to manage and control a variety of processes, including carbohydrate, fat, protein and vitamin metabolism.

The production of thyroid hormone is regulated by a hormone produced by the pituitary gland in hypothalamus at the base of the brain, and is called thyroid stimulating hormone (TSH).  When levels of thyroid hormone in the blood are low, this stimulates increased production of TSH and thereby increases production of more thyroid hormone.  Conversely, when thyroid hormone levels increase, TSH production is decreased.  This is known as a negative feedback loop, which helps maintain normal levels of thyroid hormone in the blood.

Hyperthyroidism in pets

Hyperthyroidism or thyrotoxicosis, as it is also known, is a common disorder in cats, particularly older cats and is caused by overproduction of thyroid hormone usually due to a benign enlargement of the thyroid gland.  However, hyperthyroidism is a rare condition in dogs and is usually caused by a malignant tumour called thyroid adenocarcinoma. 

The enlarged thyroid gland in cats is similar to toxic nodular goitre in humans, which is one of the major causes of hyperthyroidism in humans.  The symptoms or signs of hyperthyroidism in cats can be dramatic and can cause serious illness.  They include:

  • weight loss
  • increased appetite (polyphagia) and increased thirst (polydipsia)
  • increased food intake
  • over activity and restlessness
  • increased heartrate (tachycardia)
  • diarrhoea and vomiting
  • heat intolerance
  • change in hair coat condition
If undiagnosed or left untreated hyperthyroidism can cause more serious illness including heart failure, high blood pressure and kidney disease.  

Medical treatment 

Although surgical removal of the affected thyroid tissue is an option for treating hyperthyroidism (thyroidectomy); also radioactive iodine treatment, medical treatment is available and successful.  Anti-thyroid drugs known as thioamides like carbimazole are widely used to treat hyperthyroidism in animals and humans.  They work by blocking the synthesis of thyroid hormone and help restore high levels of thyroid hormone to normal levels.  

Medical management of hyperthyroidism with carbimazole requires daily administration and is not a cure but can be also used stabilise the animal before radiation or surgery.  
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