Alterations in the pituitary-thyroid and pituitary-adrenal axes--consequences of long-term mifepristone treatment

The effects of short-term administration of the antiprogestin and antiglucocorticoid, mifepristone, have been well characterized. However, little is known about the effects of prolonged administration of mifepristone. We analyzed hormonal parameters in four female and three male patients with unresectable meningioma who were treated with mifepristone (200 mg/d) for 20 to 40 months. Serum samples were collected at monthly intervals approximately 24 hours following mifepristone ingestion. Serum thyrotropin (TSH), thyroxine (T4), free T4 (fT4), 3,5,3-triiodothyronine (T3), prolactin, and cortisol were analyzed by fluoroimmunoassay, and androstenedione by radioimmunoassay (RIA). Levels of mifepristone and its three most proximal metabolites were measured by high-performance liquid chromatography. TSH values increased significantly (P < .005, one-way ANOVA), with the most pronounced increase evident during the first 3 months of mifepristone treatment. Despite these changes, concentrations of TSH remained within the normal range throughout the treatment period. There were no significant changes in serum T4, fT4, T3 or prolactin; however, a transient decrease in serum T4 was noted at 2 to 3 months. Cortisol and androstenedione values increased significantly and in parallel (P < .05), suggesting an adrenal origin also for androstenedione. As during short-term administration, levels of mifepristone and its metabolites remained stable in the micromolar range. Individual levels of mifepristone were significantly correlated with those of TSH and cortisol. This suggests that the alterations in the pituitary-thyroid and -adrenal axes occurred in a concentration-dependent manner. It is concluded that long-term mifepristone treatment results in resetting of the pituitary-thyroid balance. As in the case with cortisol and androstenedione, it is likely that the alterations in serum TSH are due to the antiglucocorticoid properties of mifepristone. The clinical significance of these biochemical alterations in thyroid homeostasis remains to be determined. However, monitoring thyroid function during long-term mifepristone treatment appears to be warranted.