Effects of long-term oral administration of levothyroxine sodium on serum thyroid hormone concentrations, clinicopathologic variables, and echocardiographic measurements in healthy adult horses.
Abstract: To determine the effects of long-term oral levothyroxine sodium (L-T(4)) administration on serum thyroid hormone concentrations, thyroid gland function, clinicopathologic variables, and echocardiographic examination measurements in adult euthyroid horses. Methods: 6 healthy adult mares. Methods: Horses received L-T(4) (48 mg/d) orally for 48 weeks. Every 4 weeks, physical examinations were performed; blood samples were collected for CBC, plasma biochemical analyses, and assessments of serum total triiodothyronine (tT(3)) and thyroxine (tT(4)) concentrations. Plasma creatine kinase MB activity and cardiac troponin I concentration were also measured. Echocardiographic examinations were performed before and at 16, 32, and 48 weeks during the treatment period. Results: During the treatment period, mean body weight decreased significantly; heart rate varied significantly, but the pattern of variation was not consistent. Significant time effects were detected for certain clinicopathologic variables, but mean values remained within reference ranges. Cardiac troponin I was only detectable in 8 of 24 plasma samples (concentration range, 0.01 to 0.03 ng/mL). Serum creatine kinase MB activity did not change significantly over time. Compared with the pretreatment value, 5.4-, 4.0-, and 3.7-fold increases in mean serum tT(4) concentrations were detected at 16, 32, and 48 weeks, respectively. Some cardiac measurements changed significantly over time, but mean values remained within published reference ranges. Mean fractional shortening was lower than the pretreatment mean value at 16 and 32 weeks. Conclusions: In horses, long-term oral administration of 48 mg of L-T(4)/d significantly increased serum tT(4) concentrations and did not appear to adversely affect health.
Publication Date: 2008-01-03 PubMed ID: 18167089DOI: 10.2460/ajvr.69.1.68Google Scholar: Lookup
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- Clinical Trial
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This research studied the effects of long-term ingestion of levothyroxine sodium on serum thyroid hormone levels, thyroid gland function, clinical results, and cardiac measurements in healthy adult horses. It found that while there were certain changes, there were no adverse effects on the horse’s health.
Methodology
- The study was conducted on 6 healthy adult mares.
- Each horse was administered with oral levothyroxine sodium (L-T(4)) at 48 mg/day for 48 weeks.
- Every four weeks, physical examinations were done and blood samples were taken for complete blood count, plasma biochemical analyses, and evaluation of serum total triiodothyronine (tT(3)) and thyroxine (tT(4)) concentrations.
- The activity of plasma creatine kinase MB and concentration cardiac troponin I, both important cardiac indicators, were also measured.
- Echocardiographic examinations were conducted before and at week 16, 32, and 48 of the treatment.
Results
- Overall, the horses’ average body weight decreased significantly over the treatment period.
- Fluctuations were observed in heart rate, but there was no evidence of a consistent pattern.
- While time effects were detected for certain clinicopathologic variables, the mean values stayed within the reference ranges.
- Cardiac troponin I was only detectable in 8 out of 24 plasma samples, with concentration ranging from 0.01 to 0.03 ng/mL, indicating no serious cardiac injury.
- Serum creatine kinase MB activity remained steady over time, indicating healthy muscle metabolism.
- Serum tT(4) concentrations saw an increased of 5.4-, 4.0-, and 3.7-fold at 16, 32, and 48 weeks in comparison to the pre-treatment value.
- Although some cardiac measurements changed significantly over time, these values remained within accepted reference ranges.
- Mean fractional shortening, a measurement of the heart’s pumping efficiency, was lower than the pretreatment mean value at week 16 and 32.
Conclusion
- The research concludes that, in horses, long-term oral intake of 48 mg of L-T(4)/d significantly elevated serum tT(4) concentrations.
- Despite these changes, there were no indications these fluctuations would adversely impact the horses’ health.
Cite This Article
APA
Frank N, Buchanan BR, Elliott SB.
(2008).
Effects of long-term oral administration of levothyroxine sodium on serum thyroid hormone concentrations, clinicopathologic variables, and echocardiographic measurements in healthy adult horses.
Am J Vet Res, 69(1), 68-75.
https://doi.org/10.2460/ajvr.69.1.68 Publication
Researcher Affiliations
- Department of Large Animal Clinical Sciences, College of Veterinary Medicine, University of Tennessee, Knoxville, TN 37996, USA.
MeSH Terms
- Administration, Oral
- Animals
- Drug Administration Schedule
- Echocardiography / veterinary
- Female
- Heart Rate
- Horses / physiology
- Respiration
- Thyroxine / administration & dosage
- Thyroxine / blood
- Thyroxine / pharmacology
- Triiodothyronine / blood
- Weight Loss / drug effects
Citations
This article has been cited 3 times.- Morgan R, Keen J, McGowan C. Equine metabolic syndrome. Vet Rec 2015 Aug 15;177(7):173-9.
- Anger-Håål C, Fjordbakk CT, Ekstrand C, Skedsmo FS, Rørtveit R. Sodium-glucose transporters SGLT1 and SGLT2 in equine renal, hepatic and pancreatic tissue. BMC Vet Res 2025 Dec 17;22(1):36.
- Foreman JH, Tennent-Brown BS, Oyama MA, Sisson DD. Plasma Cardiac Troponin-I Concentration in Normal Horses and in Horses with Cardiac Abnormalities. Animals (Basel) 2025 Jan 3;15(1).
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