Trilostane & Thyroid Hormones
Steroids affect thyroid hormone concentrations. Trilostane is a reversible inhibitor of steroidogenesis. In this prospective study, blood was drawn to measure thyroid hormone levels before and after 6 months of treatment with trilostane in 20 dogs with confirmed pituitary hyperadrenocorticism. Serum was assayed for total thyroxine (T4), free T4, and canine thyroid-stimulating hormone (cTSH). When data from all dogs were pooled, pre- and posttreatment findings revealed a nonsignificant increase in T4 concentrations, a significant decrease in free T4 concentrations, and a significant increase in cTSH concentrations after therapy. The decrease in free T4 was unexpected and unexplained. Study supported in part by Arnolds Veterinary Products

COMMENTARY: This study further documents that glucocorticoids suppress cTSH concentrations and that it is difficult to accurately interpret thyroid hormone concentrations in dogs receiving exogenous steroids or those with endogenously elevated glucocorticoid levels.

The effect of trilostane treatment on circulating thyroid hormone concentrations in dogs with pituitary dependent hyperadrenocorticism. Kenefick SJ, Neiger R. J SMALL ANIM PRACT 49:139-143, 2008.