Iodine-containing pharmaceuticals inducing thyroid dysfunction

Iodine is an essential component of thyroid hormones, and iodine deficiency can lead to severe hypothyroidism. On the other hand, excessive iodine intake also results in thyroid dysfunction in certain persons. Coindent described the first case of iodine-induced hyperthyroidism in 1821 (Fradkin and Wolff, 1983), and Hurxthal (1945) reported the first case of iodine-induced hypothyroidism. Ingestion of iodine-rich foods, such as seaweed, can cause hyperthyroidism, and the incidence of hyperthyroidism showed an increase in regions of dietary iodine deficiency after prophylactic iodization of bread or salt. Iodine-containing pharmaceuticals, such as povidone-iodine (PVP-I), radiographic contrast media and amiodarone, are a major source of excessive iodine intake (Wolff, 1969 Fradkin and Wolff, 1983 Markou et aL, 2001 Roti and degli Uberti, 2001). 

The effect of excessive iodine intake on thyroid function, the role of iodine-containing pharmaceuticals, and clinical aspects of iodine-induced thyroid dysfunction are discussed in this review. 

Iodine-Containing Pharmaceuticals that Induce Thyroid Dysfunction... 

There are many iodine-containing pharmaceuticals that can cause thyroid dysfunction. The majority of patients with such drug-induced thyroid dysfunction are found among those treated with inorganic iodine preparations, such as potassium iodide, sodium iodide, hydrogen iodide, or Lugols solution (Wolff, 1969 Fradkin and Wolff 1983). These days, however, the major sources of iodine... 

Development of iodine-induced thyroid dysfunction is influenced by a person s prior iodine intake. Cases of thyrotoxicosis being induced by contrast media are mainly reported in Europe or Australia, where dietary iodine levels are low, as described by Fradkin and Wolff (1983). Except for cases due to amiodarone, the incidence of iodine-induced hyperthyroidism is very low in regions where dietary iodine is adequate (Roti and degfl Uberti, 2001). Neonates treated with PVP-I often develop hypothyroidism in iodine-insufficient regions of Europe, but rarely do so in iodine-sufficient regions of the United States, as described by Brown et al. (1997). Thus, persons who five in areas where iodine is deficient in the diet are at risk of developing thyroid dysfunction induced by iodine-containing pharmaceuticals. 

Amiodarone also has intrinsic effects on the thyroid and thyroid hormone production besides those related to excessive iodine intake (Table 96.4), and this means that it induces thyroid dysfunction more frequently than any other iodine-containing pharmaceutical. 

Use of iodine-containing pharmaceuticals should be avoided, if possible, in newborn infants and pregnant women, especially in areas with a low dietary iodine intake. Individuals at risk for iodine-induced thyroid dysfunction, such as patients with previous thyroid disease or neonates, should be observed carefully to detect manifestations of thyroid dysfunction when they are treated with iodine-containing pharmaceuticals. 

Iodine-containing pharmaceuticals, such as PVP-I, radiographic contrast media and amiodarone, are a major cause of excessive iodine intake inducing thyroid dysfunction. 

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