Antithyroid Drugs for Feline Hyperthyroidism Treatment

Feline hyperthyroidism occurs when the thyroid glands are hyperactive. The condition is more common in older cats. The condition will be signaled by an increased appetite and weight loss, a poor condition of the coat and can have serious effects on the cat’s health if left untreated. The condition can be controlled with antithyroid medication or cured with surgery or radioactive ionic therapy.

The Advantages of Antithyroid Drugs

There are several types of antithyroid drugs that can be administrated as tablets 1 or 2 times per day. The drugs will control the amount of hormones secreted by the thyroid gland, preventing an excess of hormonal discharge.

The antithyroid drugs may be used as a short term or long term treatment.

The most common antithyroid drugs used for felines include:

  • Methimazole also known as felimazole, which can be administered once or twice per day, depending on the condition of the cat
  • Cabimazole also known as vidalta, which should be given once per day; it is important not to break or crush the tablets when administered to the cat

The dosage of these antithyroid drugs should be low at the beginning of the cure and increased if the cat reacts well. After 2 to 3 weeks of treatment, the level of the thyroid hormones must be measured again, to determine if the dosage is appropriate.

If the dosage is too high, the cat may secret a reduced amount of thyroid hormones and develop hypothyroidism. Periodical checkups will be necessary to monitor the thyroid hormone levels and adjust the medication dosage, if needed.

The Disadvantages of Hyperthyroidism Medication

The main disadvantage of hyperthyroidism medication is the fact that these cannot cure the cat’s condition; the drugs will only control the secretion of thyroid hormones; once the treatment is discontinued, the cat may start secreting thyroid hormones in excess. However, the antithyroid drugs may be administered for a long period of time or for life, provided the cat does not develop side effects or resistance to the drugs components.

The most frequently met side effects of antithyroid drugs include vomiting, loss of appetite and lethargy. If the side effects are severe, the vet will reduce the dosage.

In rare cases, the cat may develop skin irritations, liver problems or low white blood cell count. If these side effects occur, a different treatment should be applied.

Hyperthyroidism Treatment Options

In addition to medication therapy, hyperthyroidism may be treated using surgery or radioactive ionic treatment. These options will cure the thyroid problem.

The surgery involves the removal of the thyroid glands. There is also the option of removing only one gland, allowing the remaining to produce the thyroid hormones needed for the cat. Typically, prior the surgery, the cat needs to get some antithyroid drugs to stabilize the cat’s hormone production.

The radioactive iodine therapy will focus on eliminating the hyperactive thyroid tissues. The dormant tissues will not be affected by the therapy, so after the treatment, these dormant tissues will activate and produce a normal amount of thyroid hormones.