When Graves' Disease Patients Should Stop Methimazole Before RIT

With commentary by Jason Wexler, MD, endocrinologist at MedStar Washington Hospital Center, D.C., and Spyros Mezitis, MD, PhD, endocrinologist at Lenox Hill Hospital, New York

For years, there's been no clear agreement on the best time for Graves' Disease patients to stop taking methimazole (Tapazole) before they undergo radioactive iodine therapy or RIT. 

Graves' Disease

In Graves' disease, the thyroid gland makes excess amounts of thyroid hormones, resulting in hyperthyroidism. The medication methimazole works by preventing the thyroid gland from making too much thyroid hormone. But sometimes, it doesn't work well enough and RIT is suggested.  In RIT, the thyroid gland tissue is shrunk or destroyed. The methimazole is stopped before the RIT, ideally at a ''sweet spot"—the medication-free interval that will help the treatment work best but not make the hyperthyroidism even worse. 

Now, researchers from Iran report that responses to the RIT were the same regardless of whether patients stopped their medication one to two days before or for a longer period, even up to four days before.

"The study gets at a question that we have often wondered about," says Jason Wexler, MD, an endocrinologist at MedStar Washington Hospital Center and an assistant professor of medicine at Georgetown University. He reviewed the findings, which were published online September 29 in Nuclear Medicine Communications. 

"For many of us, we've often had the intuitive sense that people don't have to stop for as long as we have been advising them to stop. This [study] suggests that probably for the majority of patients stopping for a shorter period of time may be as effective as stopping it for a longer period of time." 

The new research is important, agrees Spyros Mezitis, MD, PhD, an endocrinologist at Lenox Hill Hospital in New York who also reviewed the findings. Withholding the medicine for more than three days, he says, may cause a worsening of the hyperthyroidism. "In our practice, we usually discontinue methimazole for 48 hours before radioiodine use with good results," he says.

The researchers, from Imam Reza Hospital and other facilities in Mashhad, Iran, evaluated 151 patients with Graves' disease, ranging from 18 to 65 years old. Before their RIT, the patients were assigned to one of three groups. They discontinued the medication one to two days before, or just over two days to three days, or just over three days to a week before. 

The researchers assessed the responses to RIT a month later, then again three months, six months and a year later. They found that the response to treatment was not different regardless of time before, up to four days before the RIT. The researchers conclude that "Shorter discontinuation of methimazole before RIT may be preferable in most patients."

Although the study provides some important information, the study follow up is brief, Dr. Wexler pointed out. "What happens after the year would be important to look at,'' he says. That way, the researchers could be sure the success of the RIT held.

In another recent study evaluating preparation for RIT for Graves' disease patients, Brazilian researchers evaluated the use of a low-iodine diet.  A low-iodine diet is often recommended for those with thyroid cancer, but its role in benign disease like Graves' is unclear, according to the researchers from the Universidade Federal de Sao Paulo and other facilities.

They assigned 67 patients with Grave's disease into two groups before they had RIT.  One ate a low- iodine diet for a week or two. The other group followed their regular diet. The researchers found no differences in how well the RIT worked six months later. That study is published online September  25 in Archives of Endocrinology and Metabolism.

Low-iodine diets are not generally advised for Graves' patients before RIT, agree Drs. Wexler and Mezitis. They are, however, often recommended before and during treatment for thyroid cancer, Dr. Wexler says. Graves' patients can be assured, Dr. Wexler says, that they would not get enough iodine from a typical, regular diet to interfere with RIT treatment.

 

 

 

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