Side Effects of Thyroxine Tablets in Dogs

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Side Effects of Thyroxine Tablets in Dogs
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Thyroxine, also called levothyroxine, is a synthetic thyroid hormone drug. When a dog has low levels of natural thyroid hormones, a veterinarian prescribes thyroxine tablets to replace the missing hormones. The thyroid hormones are important to the dog's health because they control metabolism, energy and the way the body uses food. Thyroxine tablets as hormone replacements are effective with few side effects. Typical side effects that do arise are related to dosage, allergy or drug interactions.


Your dog may have thyroid problems at any age. Call your vet when your dog gains weight easily, develops flaky skin and dry hair or has other skin problems. Skin signs may be ringworm rash or lesions on the back and belly, small dark sores on the flanks or yellow scaly layers on the skin. Your dog tires easily and is lethargic because muscles are gradually replaced by fat tissue due to thyroid changes.


Confirm thyroid gland problems through veterinary examination and lab tests. Your vet tests for thyroid problems by taking a blood sample and testing the thyroid levels. The lab sample determines how low your dog's thyroid levels are for its breed. The condition is easily treated with thyroxine or other thyroid hormone replacements.



Give your dog thyroxine tablets as prescribed. Thyroxine tablets are made in several sizes and can be divided for the recommended dose based on the dog's thyroid level and weight. Thyroxine and other levothyroxine drugs are sold under various generic and brand names. The tablet dose is given twice a day, usually every 12 hours, to maintain a steady hormone level in the body. Thyroxine takes time to build up the hormone level. Thyroid tests are usually given every 30 to 45 days until the right maintenance level is reached.


Watch your dog for signs of overdose. Too much thyroxine or levothyroxine has the same effect as hyperthyroidism, a condition when the body produces too much thyroid hormone. Signs include hyperactivity, excess water drinking or eating, frequent urination and panting, or faster heart rate. To stop these overdose-related side effects, the veterinarian would reduce the hormone medication to a lower dosage.



Call your vet if your dog has allergic reactions. Such side effects include swelling in the face, a rash, vomiting or cold limbs. An allergic reaction is not a common side effect but is serious. Different brands of thyroid medication, though they have the same main ingredient, have different effects. Brands may differ by the color dye, fillers and the way the tablet disperses the drug. Any of these can cause an allergic reaction. Your dog may need a different tablet or brand to avoid the allergy.


Advise your vet if you give the dog vitamins, supplements or other medications. Thyroxine may react with the ingredients in these products. The thyroid medication may affect other drugs such as Phenobarbital, which is used for seizures. Side effects may include lethargy, hyperactivity or aggression. Be sure to report any changes in behavior or health to your vet.



Remember that thyroxine replaces a hormone your dog needs for health. It is given the rest of the dog's life. Thyroxine is effective and, when given with care, greatly improves the dog's spirit, energy and quality of life.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.


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