Biochemical and clinical effects of fenclofenac in thyrotoxicosis.

Administration of the anti-inflammatory drug fenclofenac (600 mg bd) for 28 days to four females with thyrotoxicosis resulted in a rapid decline in thyroid hormone levels. The mean total thyroxine (T4) level of 173 +/- 8.6 (SEM) nmol/l before therapy was normalized to 70 +/- 6.4 nmol/l after administration of the drug for 7 days. Free T4 levels also decreased significantly but not to within the reference range in all subjects. Mean total triiodothyronine (T3) and reverse T3 levels declined from 6.2 +/- 0.9 nmol/l and 0.63 +/- 0.2 nmol/l respectively before therapy to 3.8 +/- 0.5 nmol/l and 0.52 +/- 0.1 nmol/l after 7 days' treatment but remained consistently elevated in all subjects. Clinical thyroid status remained unchanged despite these marked reductions in circulating thyroid hormone levels, suggesting that fenclofenac was of no therapeutic benefit.