Liothyronine (Cytobin®)

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Liothyronine (Cytobin®)

By: Dr. Karin Szust

Overview

Thyroid hormones are produced by two glands located in the neck. These hormones support normal cell function in almost every organ of the body.

The main thyroid hormone in dogs and cats is levothyroxine (also called L-thyroxin or T4). L-thyroxin is later converted to another more active thyroid hormone called T3 or triiodothyronine. If this drug is not effective, liothyronine is often prescribed as an alternative.

The thyroid hormones have significant beneficial effects on brain, heart, muscle, nerve and kidney functions and also support a healthy skin and hair coat.

When an individual cannot manufacture enough thyroid hormone to support normal cell metabolism, a condition called hypothyroidism develops.

In dogs, an autoimmune disease directed against the thyroid glands usually causes hypothyroidism, and this is often suspected in a dog with lethargy, poor hair coat, obesity and weakness.

In cats, hypothyroidism is relatively rare, and usually occurs when the thyroid glands are destroyed following thyroid gland surgery or after treatment for an over-active thyroid gland (a common condition in cats called hyperthyroidism – the opposite of hypothyroidism).

A veterinarian can only make a diagnosis of hypothyroidism after analysis of special blood tests.

It should be noted that some sick pets have slightly low thyroid hormone levels in the blood; however, this does not necessarily mean the pet has hypothyroidism. Other illnesses can temporarily depress thyroid hormone concentration.

Liothyronine is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.

Brand Names and Other Names

This drug is registered for use in humans and animals.

Human formulations: Cytomel® (SK Beecham) and various generic preparations

Veterinary formulations: Cytobin® (Pfizer)

Uses of Liothyronine

Liothyronine is used to treat hypothyroidism in patients that do not respond to levothyroxine supplementation.

Precautions and Side Effects

While generally safe and effective when prescribed by a veterinarian, liothyronine can cause side effects in some animals.

Liothyronine should not be used in animals with known hypersensitivity or allergy to the drug.

Liothyronine may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with liothyronine.

Thyroid hormone supplementation should never be administered to animals without a definite diagnosis of hypothyroidism.

Excessively high doses of liothyronine can accumulate and lead to excitement, tremors and excessive stimulation of the heart. This problem may easily be overlooked.

To ensure effective and safe dosing of liothyronine, blood tests that measure thyroid hormone levels must be obtained once the pet is receiving a consistent dose of thyroid hormone supplement.

How Liothyronine Is Supplied

Cytobin tablets are available in 60 mcg (micrograms) and 120 mcg.

Cytomel tablets are available in 5 mcg, 25 mcg and 50 mcg.

Dosing Information

Medication should never be administered without first consulting your veterinarian.

The typical dose administered to dogs is 2 to 3 mg per pound (4 to 6 mcg/kg) orally every 8 hours, but some dogs require less than this.

The dose for cats is 2 mg per pound (4.4 mcg/kg) two to three times a day orally.

Final dose adjustments are made on the basis of blood tests to measure thyroid hormone levels.