Comparative studies on the effect of noxythiolin and other thioureas on the thyroid using in vitro and in vivo models of thyroid function.

Noxythiolin (Noxyflex-S) inhibited iodide organification (thyroid hormone synthesis) by cultured porcine thyrocytes in vitro after 5 hr (IC50 approx. 9.0 microM). The positive control, the anti-thyroid thiourea methimazole, was about 15 times more potent an inhibitor of iodide organification (IC50 approx. 0.6 microM) under the same incubation conditions. In an in vivo assessment of follicular organification capacity using the perchlorate discharge test, 14 days of ip treatment of male Charles River rats with noxythiolin (50 mg/kg body weight) produced no inhibition of iodide organification when tested 24 hr after the last administration of noxythiolin whereas the positive control, propylthiouracil, was a highly potent inhibitor.