Serial Changes in Thyroid Hormones with Oral or Intravenous Bisphosphonates

Area of Science:

• Endocrinology
• Osteoporosis Management
• Thyroidology

Background:

• Bisphosphonates (BP) are crucial for osteoporosis treatment.
• The short-term endocrine effects of initial BP exposure are not well understood.
• BP therapy can trigger an acute phase response.

Purpose of the Study:

• To investigate the hypothesis that initial BP exposure induces a non-thyroidal illness syndrome (NTIS)-like pattern.
• To determine if thyroid autoimmunity amplifies the endocrine response to BP.
• To clarify the short-term endocrine effects of bisphosphonates.

Main Methods:

• Prospective cohort study of 336 adults receiving first-dose BP therapy or controls.
• Measurement of free triiodothyronine (FT3), free thyroxine (FT4), thyroid-stimulating hormone (TSH), and erythrocyte sedimentation rate (ESR).
• Analysis using linear mixed-effects models with random intercepts, adjusting for covariates.

Main Results:

• BP recipients showed a significant decline in FT3 and a modest fall in FT4.
• TSH levels were transiently suppressed and then rebounded.
• Thyroid autoimmunity (anti-TPO Ab positive) amplified FT3 suppression and TSH rebound.

Conclusions:

• First-dose BP therapy, particularly zoledronic acid (ZA), induces a transient, reversible NTIS-like endocrine response.
• Thyroid autoimmunity can amplify this BP-induced endocrine response.
• Early thyroid function tests post-BP may mimic hypothyroidism; re-evaluation after 6-8 weeks is recommended.