Pergolide does not decrease blood thyroid hormone and thyroid function in horses

Am J Vet Res. 2024 Nov 27:1-5. doi: 10.2460/ajvr.24.09.0257. Online ahead of print.

Pergolide mesylate administration does not decrease blood thyroid hormone concentrations and thyroid function in horses

Martyna M Jargielo, Janice E Kritchevsky, François-René Bertin
PMID: 39626361 DOI: 10.2460/ajvr.24.09.0257
Free article
Abstract
Objective: Pergolide, labeled for the treatment of pituitary pars intermedia dysfunction, is 90% protein bound and might cause a decrease in blood thyroid hormone concentrations by displacing them from binding proteins. This study investigated the effect of pergolide on the equine thyroid function.

Methods: This was an analytic, observational, cohort study. Six horses (17 to 24 years old and 530 to 599 kg) received 1 mg of pergolide mesylate orally once a day from days 1 to 6. Total T4 (tT4) was measured daily from day 0 to 11 (before, during, and after pergolide treatment). Thyrotropin-releasing hormone (TRH) stimulation tests were conducted on days 0 and 6. Total T3 (tT3), tT4, and free T4 by equilibrium dialysis (fT4) were measured at baseline and 2 hours (tT3) and 4 hours (tT3, T4, and fT4) after TRH administration. The effect of pergolide on thyroid hormone concentration was determined by ANOVA, with P < .05 considered significant. Results: No effect of pergolide was detected on tT4 during and after treatment. Administration of TRH resulted in significant increases in tT3 (effect size: +165.8 ng/dL [95% CI, 109.4 to 222.2 ng/dL]), tT4 (+1.162 µg/dL [95% CI, 0.7135 to 1.610 µg/dL]), and fT4 (+1.195 µg/dL [95% CI, 0.7195 to 1.670 µg/dL]). There was, however, no significant effect of pergolide on any thyroid hormone concentration. Conclusions: Pergolide has no detected effect on blood thyroid hormone concentrations and equine thyroid function. Clinical relevance: Protein-bound agents do not necessarily affect thyroid hormone concentrations. In horses with pituitary pars intermedia dysfunction, low thyroid hormone concentrations are likely due to the condition itself, not pergolide treatment. Keywords: endocrinology; hypothyroidism; nonthyroid illness syndrome; pituitary pars intermedia dysfunction; thyrotropin-releasing hormone.