Effect of Rifampin Therapy on Thyroid Function Tests in a Hypothyroid Patient on Replacement L-Thyroxine

Excerpt

Normal volunteers treated with rifampin, a potent inducer of liver microsomal enzymes, have significant decreases in serum thyroxine levels and free thyroxine index but no changes in basal or stimulated thyrotropin levels (1-3). We report the case of a patient with primary hypothyroidism receiving a constant replacement dose of L-thyroxine who developed biochemical hypothyroidism when treated with rifampin.

A 31-year-old woman with Turner syndrome and hypertension was admitted with dizziness, nausea, and vomiting. Fifteen months earlier she had had a total thyroidectomy for a rapidly enlarging goiter, which was complicated by hypoparathyroidism and recurrent laryngeal nerve palsy. Pathologic examination of