Antithyroid drugs for longterm therapy C Thiourea derivatives

(thioureylenes, thioamides) inhibit peroxidase and, hence, hormone synthesis. In order to restore a euthyroid state, two therapeutic principles can be applied in Graves' disease: a) monother-apy with a thioamide with gradual dose reduction as the disease abates; b) administration of high doses of a thio-amide with concurrent administration of thyroxine to offset diminished hormone synthesis. Adverse effects of thi-oamides are rare; however, the possibility of agranulocytosis has to be kept in mind.

Perchlorate, given orally as the sodium salt, inhibits the iodide pump. Adverse reactions include aplastic anemia. Compared with thioamides, its therapeutic importance is low but it is used as an adjunct in scintigraphic imaging of bone by means of technetate when accumulation in the thyroid gland has to be blocked.

Short-term thyroid suppression (C). Iodine in high dosage (>6000 jg/d) exerts a transient "thyrostatic" effect in hyperthyroid, but usually not in euthyr-oid, individuals. Since release is also blocked, the effect develops more rapidly than does that of thioamides.

Clinical applications include: preoperative suppression of thyroid secretion according to Plummer with Lugol's solution (5% iodine + 10% potassium iodide, 50-100 mg iodine/d for a maximum of 10 d). In thyrotoxic crisis, Lugol's solution is given together with thioamides and p-blockers. Adverse effects: allergies; contraindications: iodine-induced thyrotoxicosis.

Lithium ions inhibit thyroxine release. Lithium salts can be used instead of iodine for rapid thyroid suppression in iodine-induced thyrotoxicosis. Regarding administration of lithium in manic-depressive illness, see p. 234.

Antithyroid Drugs Action
C. Antithyroid drugs and their modes of action
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