ABNORMAL THYROID-FUNCTION TEST-RESULTS IN PATIENTS TAKING SALSALATE

Objective.-To evaluate how the nonsteroidal anti-inflammatory agent salsalate affects the results of routine thyroid function tests. Design.-In a cohort of patients taking salsalate for various rheumatic conditions, thyroid function tests were performed with patients on and off the drug. Setting.-Primary care of ambulatory patients in a university medical center. Patients.-A convenience sample of 14 euthyroid subjects, none of whom was taking thyroid hormone or other medication recognized to alter thyroid function. Intervention. -Treatment with therapeutic doses of salsalate for a mean period of 44 weeks. Main Outcome Measures.-Serum levels of thyroxine (T4), free T4, thyroid hormone binding ratio, free T4 index (the product of T4 and the thyroid hormone binding ratio), triiodothyronine, and thyrotropin. Results.-Serum T4 dropped from a mean baseline level of 96.7 nmol/L off salsalate to 53.4 nmol/L on it (P < .001), and the free T4 index showed a parallel decline from 85.9 to 50.4 (P < .001), with both values falling into the hypothyroid range. Similarly, free T4 levels and total triiodothyronine concentrations were low in several patients treated with salsalate. Serum thyrotropin levels declined transiently, falling from a mean of 3.2 to 1.7 mU/L (P < .02) in patients treated for less than 3 weeks. Patients treated for longer periods had levels comparable to baseline. Despite these changes in the thyroid function test results, all subjects remained clinically euthyroid. Conclusion.-Salsalate commonly produces abnormalities in routine thyroid function test results similar to those found in central hypothyroidism.