Thyroid medicine for dogs
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Thyroid Medicine for Dogs: An Overview
Impact of Various Medications on Canine Thyroid Function
Influence of Common Medications on Thyroid Function Tests
Several medications can significantly affect thyroid function tests in dogs, potentially leading to misdiagnosis of hypothyroidism. Drugs such as glucocorticoids, sulfonamides, phenobarbital, and nonsteroidal anti-inflammatory drugs (NSAIDs) have been shown to alter thyroid hormone physiology, including synthesis, secretion, distribution, and metabolism1 2. For instance, glucocorticoids and sulfonamides can suppress thyroid-stimulating hormone (TSH) levels, while phenobarbital can decrease total thyroxine (TT4) concentrations1 2.
Specific Drug Effects on Thyroid Function
Toceranib and Thyroid Dysfunction
Toceranib, a tyrosine kinase inhibitor used in veterinary oncology, has been associated with thyroid dysfunction in dogs. Studies have shown that while toceranib therapy does not typically result in hypothyroidism, it can cause significant elevations in TSH levels3. This necessitates regular monitoring of thyroid function in dogs undergoing toceranib treatment to avoid misinterpretation of thyroid status3.
NSAIDs and Thyroid Hormone Levels
NSAIDs, such as acetylsalicylic acid (ASA) and ketoprofen, can also influence thyroid function tests. ASA has been found to significantly decrease TT4 levels within 24 hours of administration, although it does not significantly affect free T4 (FT4) or TSH levels. Ketoprofen, on the other hand, does not appear to have a significant impact on thyroid function tests4. This suggests that thyroid function test results should be interpreted with caution in dogs receiving NSAID therapy4.
Clomipramine and Thyroid Suppression
Long-term administration of clomipramine, an antidepressant, has been shown to significantly decrease serum T4, FT4, and reverse T3 (rT3) concentrations in dogs. This reduction can lead to a misdiagnosis of hypothyroidism, although no clinical hypothyroidism was observed in the study population6. The potential for subclinical hypothyroidism exists, particularly with prolonged treatment or concurrent illness6.
Treatment of Canine Hypothyroidism
Liquid L-Thyroxine Formulation
A novel liquid formulation of levothyroxine (L-T4) has been evaluated for the treatment of canine hypothyroidism. This formulation, administered once daily, has been found to be effective and safe, with 91% of dogs showing improvement or resolution of clinical signs within four weeks5. The starting dosage of 20 micrograms per kilogram body weight was suitable for the majority of dogs, and the maintenance dose was established within 12 weeks for all dogs in the study5.
Conclusion
Understanding the effects of various medications on thyroid function is crucial for accurate diagnosis and treatment of thyroid disorders in dogs. Drugs such as toceranib, NSAIDs, and clomipramine can significantly alter thyroid hormone levels, potentially leading to misdiagnosis. For treating hypothyroidism, the liquid L-T4 formulation has proven to be an effective and safe option. Regular monitoring and cautious interpretation of thyroid function tests are essential to ensure proper management of thyroid health in dogs.
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Most relevant research papers on this topic
Influence of medications on thyroid function in dogs: An update
Drugs like amiodarone, zonisamide, and clomipramine can alter thyroid hormone physiology in dogs, leading to misdiagnosis and unnecessary treatment.
Influence of drugs on thyroid function in dogs.
Drugs like glucocorticoids, propranolol, sulfonamides, phenobarbital, potassium bromide, and NSAIDs can affect canine thyroid function, potentially leading to overdiagnosis of hypothyroidism in dogs.
Highly CitedInvestigation of thyroid function in dogs treated with the tyrosine kinase inhibitor toceranib.
Toceranib therapy in dogs is not associated with hypothyroidism but may cause elevated thyroid stimulating hormone levels, requiring monitoring.
Observational StudyInfluence of acetylsalicylic acid and ketoprofen on canine thyroid function tests.
Acetylsalicylic acid therapy can significantly decrease thyroid function in dogs, requiring cautious interpretation of thyroid function test results.
RCT
Animal StudyClinical evaluation of a novel liquid formulation of L-thyroxine for once daily treatment of dogs with hypothyroidism.
Once daily oral administration of a liquid L-T4 solution effectively and safely controls hypothyroidism in dogs, with a starting dosage of 20 microg/kg BW once daily being suitable for 79% of dogs.
Non-RCTAnimal StudyEvaluation of the effects of clomipramine on canine thyroid function tests.
Long-term clomipramine administration in dogs may lead to significant decreases in serum T4, f4, and rT3 concentrations, potentially leading to misdiagnosis of hypothyroidism.
Non-RCTAnimal StudyThe effect of imepitoin, a recently developed antiepileptic drug, on thyroid parameters and fat metabolism in healthy Beagle dogs.
Imepitoin does not affect thyroid parameters or fat metabolism in healthy Beagle dogs, while phenobarbital may decrease thyroxine levels over time.
Non-RCTAnimal StudyToceranib phosphate in the treatment of canine thyroid carcinoma: 42 cases (2009-2018).
Toceranib phosphate provides clinical benefit and minimal adverse effects in dogs with thyroid carcinoma, regardless of whether they have prior therapy or not.
Observational StudyThe effect of trilostane treatment on circulating thyroid hormone concentrations in dogs with pituitary-dependent hyperadrenocorticism.
Trilostane treatment in dogs with pituitary-dependent hyperadrenocorticism increased canine thyroid-stimulating hormone levels, but did not significantly change thyroxine levels.
Non-RCTAnimal StudyEffect of trimethoprim/sulfamethoxazole on thyroid function in dogs with pyoderma.
Trimethoprim/sulfamethoxazole treatment in dogs with pyoderma may cause hypothyroidism and may lead to incorrect diagnosis of inadequate thyroid function.
Non-RCTAnimal Study