[The effects of diclofenac sodium on thyroid function tests in vivo and in vitro]

In order to investigate the effects of the non-steroidal antiinflammatory drug, diclofenac sodium on thyroid function, 8 male and 2 female volunteers were given single dose of 50 mg diclofenac sodium. Ninety minutes after the administration of the drug, the concentrations of total T 3, total T 4 and free T 4 were decreased significantly, but the concentrations of free T 3 and the levels of T 3 uptake, % free T 3 and % free T 4 were increased. When diclofenac sodium was added to serum in vitro, the levels of free T 3, free T 4 and T 3 uptake were increased. These results showed that diclofenac sodium inhibited the binding of T 3 and T 4 competitively to the binding protein. The apparent decline in the concentrations of total T 3 and total T 4 after diclofenac sodium administration suggested that the drug altered distribution and metabolism of T 3 and T 4 mainly by increasing their free forms.