Transient changes in thyroid functions tests after zoledronic acid infusion.

Zoledronic acid (ZA) induces an acute phase response in association with elevation of serum cytokines, which possibly alter the 3 types of iodothyronine deiodinase activity. We therefore studied the possible alteration in thyroid function tests by ZA. We investigated the acute changes in serum thyroid hormones, TSH, cortisol, white blood cells, CRP, interleukin-6 (IL-6) and tumor necrosis factor (TNF-α), before (0) and 1, 2 and 3 days after iv infusion of 5 mg ZA in 24 asymptomatic postmenopausal women with osteoporosis (ZA group) in comparison with a placebo group. In the majority of patients the ZA infusion was associated with acute phase response and fever within 24h after infusion which became attenuated on day three. Concurrently with increase in serum cortisol, CRP, IL-6 and TNF-α, on day 1 and 2, total serum T3 (TT3), free T3 (fT3), total T4 (TT4) and fT4 decreased with a nadir on day 2 in association with an increase in the fT4/fT3 ratio and reverse T3 (rT3) levels. All thyroid function changes returned to the baseline levels on day 3, with cytokines still at higher levels, although lower than those on day 2. Serum TSH remained essentially unchanged throughout the study. The changes in thyroid hormones were at least in part explained by the increased TNF-α, but not by IL-6. ZA induces short term changes in thyroid hormones, characteristic of nonthyroidal illness syndrome (NTIS), in association with an increase in TNF-α and IL-6.