| Tests of thyroid function may be especially affected when several agents are given together. For example, the concurrent use of high dose furosemide with dopamine can result in profound hypothyroxinemia (Stockigt et al, 1984). Infusion of furosemide in high dosage displaces T4 from TBG, thereby causing its accelerated clearance, while concurrent dopamine infusion inhibits the normal TSH response to hypothyroxinemia. When dopamine is ceased, serum TSH can rise transiently to supranormal levels which can be mistakenly interpreted as indicating primary hypothyroidism, followed by spontaneous normalization of both serum T4 and TSH. The combination of rifampicin, which accelerates T4 clearance, with glucocorticoid-induced inhibition of TSH secretion can have a similar effect. |
