Endocrine Abstracts

Background: Iopanoic acid is an iodinated oral cholecystographic contrast agent, which can be used for the rapid blockade of thyroid hormone production in preparation for thyroidectomy, especially in patients who are intolerant of thionamides. However, appropriate timing of thyroid surgery is vital.

Project: In this retrospective audit, we identified all patients with thyrotoxicosis who received pre-operative preparation with iopanoic acid from 2006 to 2009 and evaluated appropriateness of patient selection, administration, monitoring, time to normalisation of fT₄ and fT₃ levels, timing and complications of thyroid surgery.

Outcomes: We identified five patients. All patients had Graves’ disease. The indication for iopanoic acid- assisted thyroidectomy was neutropaenia on thionamides (n=1), and uncontrolled thyrotoxicosis despite thionamides (n=4). The mean time from commencement of iopanoic acid to thyroidectomy was 13.6 days (range 10–20 days, median 12 days). By the time of thyroid surgery, 100% patients achieved fT₃ levels within the reference range and 40% achieved normal or near-normal fT₄ levels. Time to normalisation of fT₃ levels correlated with baseline fT₃. There were no anaesthetic or surgical complications.

Conclusions: Preoperative rapid blockade of thyrotoxicosis with iopanoic acid is safe and efficacious in a supervised environment. The optimum duration of treatment is 12–14 days. However, there is a positive correlation between the pre-iopanoic acid fT₄ and fT₃ levels and time taken for their normalisation. fT₃ levels appear to be a better indicator of safety for surgery than fT₄. This audit assists in the planning of the timing of thyroidectomy when iopanoic acid is used.