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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.

Systemic side-effects during irrigation of body cavities with the antiseptic noxythiolin (Noxyflex) have not previously been reported. In two patients undergoing intrapleural lavage with 1% noxythiolin, anorexia and nausea with or without vomiting were observed which suggested systemic absorption. This was confirmed by chemical assays of serum from these patients. The process of absorption was studied in rabbits by injection of noxythiolin into the pleural or peritoneal cavity. Serum levels reached a peak at one to two hours indicating rapid entry into the bloodstream, declined slowly over seven hours, and reached zero before 24 hours. Although side-effects resulted from systemic absorption of noxythiolin during irrigation of the pleural cavity, they were mild and did not contra-indicate the use of noxythiolin as an irrigant. Awareness of the mechanism of side-effects of noxythiolin provides a rational basis for management of symptoms through reduction of the volume or frequency of irrigation.