Effect of Cyclic Administration of Certain Progestin-Estrogen Combinations on the 24-Hour Radioiodine Thyroid Uptake

Abstract

The effects of short- and long-term administration of a mixture of pro-gestogen and estrogen in different doses on the 24-hr. radioiodine uptake by the thyroid gland were studied in a group of 154 women. EE3ME (ethinyl estradiol-3-methyl ether) was the estrogen used in all cases, while norethynodrel (17[beta]-ethinyl-estra-5,10-eneolone) and ethynodioldi-acetate (17[beta]-ethinyl-4-estrene-3,17-diol-diacetate) were the progestogens. In all cases the compounds were administred daily, from the 5th through the 24th day of each cycle. The dosage schedule and duration of medication were as follows: Norethynodrel 5 mg and EE3ME 0.075 mg for 3 months in short-term users and for over 3 years in long-term users; norethynodrel 2.5 mg and EE3ME 0.1 mg after 3 years of use; ethynodioldi-acetate 1 mg with EE3ME 0.1 mg and 2 mg with EE3ME 0.1 mg, both for 3 months. Statistical analysis of the results showed no significant difference between the average of the long-term users and those of the controls, or between the results of the tests before and after medication in the short-term users, with the exception of those taking ethynodioldi-acetate 2 mg. The variation in this group, though significant by the t test, falls within the accepted day-to-day variation of radioiodine uptake and well within the limits of normal variation for euthyroid patients, so it is of no clinical importance.