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Pharmacokinetics of Total Thyroxine after Repeated Oral Administration of Levothyroxine Solution and its Clinical Efficacy in Hypothyroid Dogs

BACKGROUND: Oral levothyroxine (l‐T(4)) supplementation is commonly used to treat hypothyroid dogs. OBJECTIVES: Investigate the plasma profile and pharmacokinetics of total thyroxine (tT(4)) after PO administration of a l‐T(4) solution and its clinical efficacy in hypothyroid dogs. ANIMALS: Ten dogs...

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Detalles Bibliográficos
Autores principales: van Dijl, I.C., Le Traon, G., van de Meulengraaf, B.D.A.M., Burgaud, S., Horspool, L.J.I., Kooistra, H.S.
Formato: Online Artículo Texto
Lenguaje:English
Publicado: John Wiley and Sons Inc. 2014
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4857956/
https://www.ncbi.nlm.nih.gov/pubmed/24773132
http://dx.doi.org/10.1111/jvim.12363
Descripción
Sumario:BACKGROUND: Oral levothyroxine (l‐T(4)) supplementation is commonly used to treat hypothyroid dogs. OBJECTIVES: Investigate the plasma profile and pharmacokinetics of total thyroxine (tT(4)) after PO administration of a l‐T(4) solution and its clinical efficacy in hypothyroid dogs. ANIMALS: Ten dogs with naturally occurring hypothyroidism. METHODS: After hypothyroidism diagnosis and supplementation with l‐T(4) solution PO q24h at 20 μg/kg BW for minimum 4 weeks, the plasma profile and pharmacokinetics of tT(4) were determined over 34 hours and the clinical condition of the dogs was evaluated. RESULTS: Before dosing for pharmacokinetic evaluation, mean tT(4) concentration was 23 ± 9 nmol/L. l‐T(4) was absorbed rapidly (t (max), 5 hours), reaching a mean maximal tT(4) concentration of 56 ± 11 nmol/L. The apparent terminal half‐life was 11.8 hours. Clinical signs of hypothyroidism improved or resolved in all dogs after 4 weeks of treatment. The dosage of 20 μg/kg PO q24h was judged appropriate in 5 dogs, and 4 dogs required slight increases (9–16%). Twice daily treatment, with a 30% increase in dosage, was necessary for 1 dog. CONCLUSIONS AND CLINICAL IMPORTANCE: The pharmacokinetics of l‐T(4) in hypothyroid dogs was similar to that reported in healthy euthyroid dogs. Clinical and hormonal responses to l‐T(4) solution were rapid in all dogs. The starting dosage of 20 μg/kg PO q24h was suitable for maintenance supplementation in 50% of the dogs, minor dosage modification was required in 4 other dogs, and treatment q12h was required in 1 dog.