COMPARATIVE EFFECTS OF SODIUM IPODATE AND IODIDE ON SERUM THYROID HORMONE CONCENTRATIONS IN PATIENTS WITH GRAVES' DISEASE

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Abstract
Patients with thyrotoxic Graves'' disease were treated daily for 10 d with 1 g sodium ipodate, an iodine rich X-ray contrast agent which impairs outer ring (5''-) deiodination of T4 [thyroxine] to T3 [triidothyronine], or with 12 drops of a saturated solution of potassium iodide (SSKI). T4, T3 and reverse T3 (rT3) concentrations were measured before, during, and 5 and 10 d after the administration of each drug. SSKI therapy induced a decrease in the serum T4 concentration from 14.7 .+-. 1.3 .mu.g/dl (mean .+-. SE) to a nadir of 7.9 .+-. 0.9 on days 9 and 10 of therapy, all values reaching the normal range by day 9; a decrease in the serum T3 concentration from 402 .+-. 43 ng/dl to a nadir of 143 .+-. 20 on day 10, remaining elevated in all patients until day 5 and decreasing into the normal range in all except one patient on days 9 and 10; and no change in the serum rT3 concentration. Serum T4 and T3 concentrations returned to baseline values 10 d after withdrawal of SSKI. Sodium ipodate therapy induced only a modest decrease in the serum T4 concentration from 15.1 .+-. 0.7 .mu.g/dl to a nadir on day 9 of 11.3 .+-. 1.0 and serum T4 remained above the norma range in most patients until day 8; a striking and rapid decrease (within 12 h) in the serum T3 concentration from 340 .+-. 36 ng/dl to mean values ranging from 79 to 85 during the last 5 d of therapy, with most values below the normal range during the last 3 d; and a marked increase in the serum rT3 concentration from 111 .+-. 15 ng/dl to a peak value of 376 .+-. 59 on day 5. A significant rebound increase in serum T4 (18.7 .+-. 1.7 .mu.g/dl; P < 0.01) and serum T3 (512 .+-. 72; P < 0.01) concentrations as compared to pretreatment values occurred 10 days after sodium ipodate was discontinued. Although treatment of hyperthyroidism with sodium ipodate induced a more rapid and more profound decrease in the serum T3 concentration than did SSKI, a marked rebound increase in serum T4 and T3 concentrations occurred after withdrawal of sodium ipodate but not after SSKI was discontinued.