January 15, 2021

The FDA’s Center for Veterinary Medicine has approved ThyroKare (levothyroxine sodium tablets), the second levothyroxine sodium product approved for replacement therapy for diminished thyroid function in dogs. 

Hypothyroidism occurs when the thyroid gland doesn’t produce and secrete enough thyroid hormones, and these hormones play a big role in metabolism and affect the function of many parts of the body. Hypothyroidism is a common hormone imbalance in dogs and is usually caused by inflammation or shrinkage of the thyroid gland. This progressive destruction of the gland leads to diminished thyroid function and insufficient levels of thyroid hormones. Hypothyroidism is typically seen in middle-aged to older dogs and occurs more commonly in medium to large breed dogs. 

This approval is an example of the FDA’s commitment to the identification and use of alternative methods to meet the requirements for new animal drug approvals. As an alternative to conducting laboratory animal studies, the FDA evaluated a range of sources that demonstrate the safety of ThyroKare in dogs. These sources included (1) a comprehensive review of publicly available literature on the use of levothyroxine in dogs; (2) pharmacovigilance data for ThyroKare that were voluntarily reported to the sponsor when it was previously marketed as an unapproved drug; and (3) reports to an animal poison control center of accidental overdoses of natural or synthetic thyroid hormone products in dogs. 

The sponsor of ThyroKare conducted a field effectiveness and safety study in client-owned dogs that were diagnosed with hypothyroidism but had never been treated with levothyroxine sodium. Owners administered ThyroKare orally to their dog every 12 hours. On Day 84, 87 of 107 dogs (81.3%) evaluated for effectiveness were a treatment success based on thyroid hormone levels. The clinical signs of hypothyroidism also improved during the study. The most common adverse reactions were polydipsia (thirst), polyuria (excessive urination), tachypnea (abnormal/fast breathing), lethargy, anorexia (loss of appetite), emesis (vomiting), and muscle tremors or shaking. 

ThyroKare is available by prescription only because professional expertise is required to diagnose hypothyroidism and to monitor the safe use of the product, including treatment of any adverse reactions. Monitoring typically includes regular evaluations of thyroid hormone levels to ensure the prescribed dose of the product remains at an appropriate level to manage the disease. Monitoring is also important when switching to another levothyroxine sodium product due to potential differences in recommended doses and in bioavailability. 

ThyroKare is available in nine strengths of color-coded tablets from 0.1 to 1 mg, in bottles of 180 and 1,000 tablet counts. 

ThyroKare is sponsored by Neogen Corp. based in Lexington, Kentucky. 

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Freedom of Information Summary