Radioactive iodide (131 I-) excretion profiles in response to potassium iodide (KI) and ammonium perchlorate (NH4ClO4) prophylaxis.

Radioactive iodide ((131)I-) protection studies have focused primarily on the thyroid gland and disturbances in the hypothalamic-pituitary-thyroid axis. The objective of the current study was to establish (131)I- urinary excretion profiles for saline, and the thyroid protectants, potassium iodide (KI) and ammonium perchlorate over a 75 hour time-course. Rats were administered (131)I- and 3 hours later dosed with either saline, 30 mg/kg of NH(4)ClO(4) or 30 mg/kg of KI. Urinalysis of the first 36 hours of the time-course revealed that NH(4)ClO(4) treated animals excreted significantly more (131)I- compared with KI and saline treatments. A second study followed the same protocol, but thyroxine (T(4)) was administered daily over a 3 day period. During the first 6-12 hour after (131)I- dosing, rats administered NH(4)ClO(4) excreted significantly more (131)I- than the other treatment groups. T(4) treatment resulted in increased retention of radioiodide in the thyroid gland 75 hour after (131)I- administration. We speculate that the T(4) treatment related reduction in serum TSH caused a decrease synthesis and secretion of thyroid hormones resulting in greater residual radioiodide in the thyroid gland. Our findings suggest that ammonium perchlorate treatment accelerates the elimination rate of radioiodide within the first 24 to 36 hours and thus may be more effective at reducing harmful exposure to (131)I- compared to KI treatment for repeated dosing situations. Repeated dosing studies are needed to compare the effectiveness of these treatments to reduce the radioactive iodide burden of the thyroid gland.

Total thyroidectomy for amiodarone-associated thyrotoxicosis: should surgery always be delayed for pre-operative medical preparation?

OBJECTIVE: Amiodarone can induce severe hyperthyroidism that justifies its withdrawal and the introduction of antithyroid drugs. Continuing amiodarone use, failure to control hyperthyroidism and poor clinical progress may require thyroidectomy. This study aimed to evaluate patients' post-operative development and mid-term outcome after thyroidectomy for amiodarone-associated thyrotoxicosis. STUDY DESIGN: Prospective case series. SETTING: Tertiary care centre. SUBJECTS AND METHODS: We prospectively collected cases of amiodarone-associated thyrotoxicosis requiring thyroidectomy due to failure of antithyroid treatment, despite amiodarone discontinuation. Post-thyroidectomy complications were compared immediately, 30 days and one year post-operatively, and also for scheduled versus emergency surgery cases. RESULTS: Of 11 total cases, nine scheduled thyroidectomy cases had no morbidity after elective surgery. Two cases required emergency surgery for multiple organ failure and cardiac problems. Immediate post-operative complications (mostly haemodynamic) occurred in both cases (emergency vs routine surgery, p = 0.018). CONCLUSION: In such cases, pre-operative medical treatment is vital to limit peri- and post-operative complications, but surgery should not be delayed if the haemodynamic status deteriorates. Surgery, with careful anaesthesia, is the cornerstone of the treatment.

Evaluation of potassium iodide (KI) and ammonium perchlorate (NH4ClO4) to ameliorate 131I- exposure in the rat.

Nuclear reactor accidents and the threat of nuclear terrorism have heightened the concern for adverse health risks associated with radiation poisoning. Potassium iodide (KI) is the only pharmaceutical intervention that is currently approved by the Food and Drug Administration for treating (131)I(-) exposure, a common radioactive fission product. Though effective, KI administration needs to occur prior to or as soon as possible (within a few hours) after radioactive exposure to maximize the radioprotective benefits of KI. During the Chernobyl nuclear reactor accident, KI was not administered soon enough after radiation poisoning occurred to thousands of people. The delay in administration of KI resulted in an increased incidence of childhood thyroid cancer. Perchlorate (ClO(4)(-)) was suggested as another pharmaceutical radioprotectant for 131I- poisoning because of its ability to block thyroidal uptake of iodide and discharge free iodide from the thyroid gland. The objective of this study was to compare the ability of KI and ammonium perchlorate to reduce thyroid gland exposure to radioactive iodide (131I-). Rats were dosed with 131I- tracer and 0.5 and 3 h later dosed orally with 30 mg/kg of either ammonium perchlorate or KI. Compared to controls, both anion treatments reduced thyroid gland exposure to 131I- equally, with a reduction ranging from 65 to 77%. Ammonium perchlorate was more effective than stable iodide for whole-body radioprotectant effectiveness. KI-treated animals excreted only 30% of the (131)I(-) in urine after 15 h, compared to 47% in ammonium perchlorate-treated rats. Taken together, data suggest that KI and ammonium perchlorate are both able to reduce thyroid gland exposure to 131I- up to 3 h after exposure to 131I-. Ammonium perchlorate may offer an advantage over KI because of its ability to clear 131I- from the body.

Amiodarone-induced thyrotoxicosis. A review.

Amiodarone (AM), a potent class III anti-arrhythmic drug, is an iodine-rich compound with a structural resemblance to thyroid hormones triiodothyronine (T3) and thyroxine (T4). At the commonly employed doses, AM causes iodine overload up to 50-100 times the optimal daily intake, which may be responsible of a spectrum of effects on thyroid function often counterbalancing its heart benefits. Although most patients on chronic AM treatment remain euthyroid, a consistent proportion may develop thyrotoxicosis (AM-induced thyrotoxicosis, AIT) or hypothyroidism. AIT is more prevalent in iodine-deficient areas and is currently subdivided in two different clinico-pathological forms (AIT I and AIT II). AIT I develops in subjects with underlying thyroid disease, and is caused by an exacerbation by iodine load of thyroid autonomous function; AIT II occurs in patients with no underlying thyroid disease and is probably consequent to a drug-induced destructive thyroiditis. Mixed or indeterminate forms of AIT encompassing several features of both AIT I and AIT II may be also observed. The differential diagnosis between AIT I and AIT II (which is important for the choice of the appropriate therapy) is currently made on radioiodine uptake (RAIU), which may be high, normal or low but detectable in AIT I, while is consistently very low or undetectable in AIT II and on colour-flow Doppler sonography (CFDS) showing normal or increased vascularity in AIT I and absent vascularity in AIT II. Quite recently, studies carried out in our Units at the University of Cagliari (Italy) showed that sestaMIBI thyroid scintigraphy may represent the best single test to differentiate AIT I (showing increased MIBI retention) from AIT II (displaying no significant uptake). Treatment of AIT is dependent from its etiology. AIT usually responds to combined thionamides and potassium perchlorate (KClO4) therapy, AIT II generally responds to glucocorticoids, while indeterminate forms may require both therapeutic approaches. In patients with AIT I definitive treatment of hyperthyroidism by administration of (131)I, initially not feasible for the low RAIU and/or the risk of thyrotoxicosis exacerbation, is advised after normalization of iodine overload. To control severe AIT additional treatment with lithium carbonate, the use of short course of iopanoic acid and plasmapheresis have been also proposed. In cases resistant to medical treatment and/or in patients with severe cardiac diseases who cannot interrupt AM or require quick AM reintroduction, total thyroidectomy (possibly carried out by minimally invasive video-assisted technique) may be proposed after rapid correction of thyrotoxicosis with combination of thionamides, KClO4, corticosteroids and a short course of iopanoic acid.

[Treatment of amiodarone-induced hyperthyroidism: corticosteroids or potassium perchlorate? What value do interleukin-6 levels have?]. / Traitements de l'hyperthyroïdie induite par l'amiodarone: corticoïdes ou perchlorate de potassium? Qu'apporte le dosage d'interleukin-6?

We report 11 cases of amiodarone-induced hyperthyroidism. We tried to classify them into 2 groups, according to Bartelena et al. (JCEM 81: 2930, 1996). The serum level of interleukin-6 (IL-6) was measured in 7 patients by an immunoenzymometric assay. In type I (cases 1-3) the thyroid was abnormal (goiter, Graves' disease) but IL-6 levels were normal. These cases were successfully managed by the combined use of thionamide drugs (carbimazol or propylthioruacil = PTU) and potassium perchlorate. In type II (case 4), the thyroid seemed to be normal but the serum level of IL-6 was increased, possibly due to a destructive thyroiditis. Treatment with prednisone (40 mg/day) and PTU resulted in a prompt normalization of T3. Contrary to Bartalena et al., we observed cases with normal thyroid and normal levels of IL-6 (cases 5-8) (type III). In these cases prednisone (40 mg/day for 2 weeks) was ineffective but the combined use of thionamide drugs and perchlorate was associated with a normalization of thyroid hormones. This combined treatment seems to be effective in most patients (type I, III). In case of failure of this treatment, a high dose of prednisone (1 mg/kg) could be tried or a lower dosage (40 mg/day) could be used in cases with high IL-6 levels (type II).

Thyroid radiation doses during radioimmunotherapy of CEA-expressing tumours with 131I-labelled monoclonal antibodies.

A number of radioimmunotherapy (RAIT) trials with iodinated antibodies have shown a high variability in the radiation doses to the thyroid. Therefore, the aim of this study was to evaluate which factors influence these thyroid doses during RAIT with 131iodinated monoclonal anti-carcinoembryonic antigen (CEA) antibodies. Data from 36 patients with CEA-expressing tumours were analysed. The patients underwent RAIT with the 131I-labelled IgG1 anti-CEA antibody, MN-14 (Ka = 10(9) l mol-1) or its F(ab')2 fragment (activity range 45.8-220.0 mCi). The thyroid was blocked with 120 mg iodine (lugol's orSSKI solution) and 400 mg perchlorate per day, starting 1 day prior to the first study. Blood clearance and molecular composition of labelled plasma compounds were determined by blood sampling and size-exclusion high-performance liquid chromatography analysis. The cumulated activities of tissues were determined from daily imaging and blood clearance data. Doses were derived from the MIRD scheme. Thyroid radiation doses showed a high variability, between 1.2 and 37.7 cGy mCi-1 (mean +/- S.D.: 11.1 +/- 8.3 cGy mCi-1), corresponding to absolute doses between 2.5 and 43.6 Gy. However, the maximal iodine uptake in the thyroid was 2.4 +/- 1.9 microCi mCi-1 (range 0.2-10.0 microCi mCi-1), which was less than 1% of the injected activity, indicating that more than 99% of the thyroid was blocked in all cases. No correlation was found between these thyroid doses and conditions leading to an enhanced exposure to free radioiodine, such as unbound I- in the mAb preparation, rapid metabolic breakdown of the labelled antibody due to human anti-mouse antibodies (HAMA), or immune complex formation with circulating antigen. However, a relationship between the thyroid doses and the patients' compliance in taking their Lugol's and perchlorate blocking medications, as well as to a relatively high variability in the biological half-life of the iodine in the thyroid (range from 31.1 h to virtual infinity), is indicated. No rising TSH titres or other signs of (latent) hypothyroidism were seen in these patients during a 2 year follow-up period. Longer follow-up was not possible because of the terminal condition of most of the patients. These data show that thyroid doses in an appropriately blocked individual given a standard, non-myeloablative dose of RAIT, are generally lower than those assumed to be required to cause late hypothyroidism. Even if higher activities are used, potential hypothyroidism may be overcome easily by hormone replacement. Thyroid doses are independent of parameters leading to an enhanced exposure of the thyroid to free radioiodine, suggesting that patient compliance in taking their blocking medication may be the most crucial factor for reducing thyroid doses in RAIT with 131I-labelled antibodies.

Treatment of amiodarone-induced thyrotoxicosis, a difficult challenge: results of a prospective study.

Amiodarone-induced thyrotoxicosis (AIT) occurs in both abnormal (type I) and apparently normal (type II) thyroid glands due to iodine-induced excessive thyroid hormone synthesis in patients with nodular goiter or latent Graves' disease (type I) or to a thyroid-destructive process caused by amiodarone or iodine (type II). Twenty-four consecutive AIT patients, 12 type I and 12 type II, were evaluated prospectively. Sex, age, severity of thyrotoxicosis, and cumulative amiodarone dose were similar. Type II patients had higher serum interleukin-6 (IL-6; median, 440 vs. 173 fmol/L; P < 0.001), but lower serum thyroglobulin levels. Several weeks of thionamide therapy in eight type II or prolonged glucocorticoid administration in two type I patients had previously failed to control hyperthyroidism. Type II patients were given prednisone (initial dose, 40 mg/day) for 3 months and achieved normal free T3 and IL-6 after an average of 8 and 6 days, respectively. Exacerbation of thyrotoxicosis with increased serum IL-6 values, observed in 4 patients while tapering steroid, was promptly corrected by increasing it. Type I patients, given methimazole (30 mg/day) and potassium perchlorate (1 g/day), achieved normal free T3 and IL-6 concentrations after an average of 4 weeks. Exacerbation of thyrotoxicosis with markedly increased IL-6 was controlled by prednisone in 3 of 4 cases. Distinction of different forms of AIT is essential for its successful management. Type II AIT should be treated with glucocorticoids; type I AIT should be treated with methimazole and potassium perchlorate. Exacerbation of thyrotoxicosis, which may occur in both forms and is probably related to destructive processes, should be controlled by the addition/increase in glucocorticoids.