Lithium and iodine combination therapy for thyrotoxicosis

Abstract

Abstract. In order to compare the relative therapeutic efficacy of iodine (I) and lithium (Li) in thyrotoxicosis, investigate possible additive effects of these agents, and examine their effect upon thyroidal release, 17 thyrotoxic patients were assigned to groups given either I (n = 9) or Li (n = 8) alone during an initial treatment period, with the alternate drug added as combination treatment during a second treatment period. Half of the patients received methimazole (MMI). Three additional thyrotoxic patients received I during both treatment periods to evaluate the possibility of cumulative I effect upon thyroidal release during the second treatment period. A double isotope technique was utilized as an index of thyroidal release, employing 125I as an intra-thyroidal label and [131I] T4 as a marker of T4 disposal. During the first treatment period either I or Li induced comparable, significant (P < 0.05) decreases in thyroidal release, as measured by slopes of ratios of serum PB125I: PB131I and by percentage inhibition of fractional T4 release rate. In response to Li, there was a 55% decrease in the slope of PB125I: PB131I with MMI and a 52% decrease without MMI. In response to I, there was a 70% dercrease in the slope of PB125I: PB131I with MMI and a 57% decrease without MMI. Further significant (P < 0.05) decreases in the slopes of these ratios during the second, combined treatment period (I + Li) occurred only in those patients who had initially received I. No further decreases in the second treatment period were seen in patients receiving I during both treatment periods. Thus, I and Li together display additive inhibition of thyroidal release only if I is administered initially, but the combination, if Li is used first, does not appear to be more effective than Li alone.