Fenclofenac-secondary effects upon the pituitary thyroid axis.

Area of Science:

• Endocrinology
• Pharmacology
• Thyroid Research

Background:

• Fenclofenac therapy is known to suppress TSH response to TRH.
• The precise mechanism behind this suppression requires further elucidation.

Purpose of the Study:

• To investigate the early effects of fenclofenac on TSH responsiveness to TRH.
• To assess fenclofenac's impact on other pituitary hormone responses.
• To evaluate fenclofenac's interference with free thyroid hormone assays.

Main Methods:

• Detailed examination of the early period of fenclofenac administration.
• Assessment of fenclofenac's effect during TRH infusion.
• Evaluation of fenclofenac's impact on pituitary hormone responses to insulin-induced hypoglycemia.
• Analysis of fenclofenac's effect on equilibrium dialysis for free thyroid hormone estimation.

Main Results:

• Fenclofenac caused a transient, sharp increase in free thyroxine levels shortly after the first dose.
• Repeated peaks in free thyroxine during chronic treatment, alongside a decline in total thyroxine, are proposed to cause TSH suppression.
• Pituitary suppression appeared secondary to elevated free thyroxine levels.
• Fenclofenac did not affect ACTH, cortisol, growth hormone, or prolactin responses to hypoglycemia.

Conclusions:

• The transient rise in free thyroxine induced by fenclofenac is the likely cause of suppressed TSH responsiveness to TRH.
• Fenclofenac does not significantly interfere with free thyroid hormone assays within therapeutic ranges.
• Fenclofenac does not impact other pituitary axes examined.