[Effect of universal salt iodization on the dosage of antithyroid drug]

To investigate the effect of universal salt iodization (USI) on antithyroid drug.

One hundred and one patients with untreated hyperthyroidism were randomly divided into two sex and age-matched groups: group A (n = 45, consuming pure salt without iodine) and group B (n = 56, consuming iodated salt). The same dosage of 300 mg propylthiouracil (PTU) was given to both groups at beginning, the serum TT4. TT3, FT4, FT3, and TSH were measured before and 1, 2, 3, 6 months after PTU treatment, when the serum TT4, TT3, FT4. FT3, and TSH were back to the normal ranges, the dosage of PTU was decreased to maintain the normal levels of serum thyroid hormones.

The urine iodine and serum thyroid hormone levels were not significantly different between group A and group B before the treatment (P > 0.05). The urine iodine of group A was significant lower 2 - 3 months after the treatment (148.4 micro g/L) than before the treatment (213.4 micro g/L, P < 0.01). There were not significant differences in serum TT4, TT3, FT4, and FT3 between group A and B before the treatment (all P > 0.05). One month after the treatment the serum TT4 and TT3 in group A were (153 +/- 50) nmol/L and (3.6 +/- 1.2) nmol/L respectively, both significantly lower than those of the group B [(177 +/- 64) nmol/L and (2.7 +/- 1.5) nmol/L respectively, P = 0.041 and 0.033], however, there was no significant difference in other serum thyroid hormones between the group A and group B. The dosage of PTU was not significantly different between group A and B 1 month after the treatment, but became significantly higher in group B than in group A 2, 3, and 6 months after the treatment (214,189, and 178 mg/d respectively vs. 190, 147, and 116 mg/d respectively, and 24, 42, and 62 mg/day more respectively, all P < 0.05).

Hyperthyroidism can be effectively controlled by PTU while the patients consume iodated salt, but the dosage of PUT needed should be higher than while the patients consume pure salt.