Is it My Thyroid? Look Out for These Common Thyroid Drug Interactions

Medical science has come a long way in recent decades, and patients with thyroid disorders have reaped the benefits of these advances. With proper adherence to a prescribed treatment regimen, most men and women with common thyroid disorders such as hypothyroidism and hyperthyroidism can live normal, full lives.

However, because the rate of new drug development often outpaces the number of drug interaction studies that can be conducted, it is often virtually impossible for doctors to keep up with all of the possible complications that can occur when thyroid medications are combined with other drugs. Conversely, scientists continue to be on the lookout for drug combinations that can cause, exacerbate, or worsen existing thyroid problems.

As a result, it’s very important for patients with thyroid disorders – and even those with normal thyroid function who have special concerns about maintaining thyroid health – to keep a close eye on possible drug interactions. This week, we’ll take a look at the results of several recent studies that have documented potential problems.

Anti-Tumor Medication Can Slow Thyroid Function

A drug that can impede the development of tumors is always a boon to cancer patients, and years of intensive testing has shown that the medication Sunitinib can indeed slow the growth of certain types of cancer, including kidney and gastrointestinal forms of the disease.

However, according to the results of a study recently published in the Annals of Internal Medicine, Sunitinib’s effectiveness as an anti-tumor agent may come at a significant price. Scientists confirmed previous suspicions that prolonged use of the drug can slow thyroid function and even cause hypothyroidism in some cases.

In the study, thyroid function was studied in a group of 42 patients who had been diagnosed with cancer and were using Sunitinib as part of their treatment regimen. None of the patients participating in the study had a history of hypothyroidism or slowed thyroid function.

When the results of the study were analyzed, it was found that 36% met the clinical criteria for a diagnosis of hypothyroidism. Among the patients who did not meet the criteria for hypothyroidism, an additional 15% were found to have low bloodstream concentrations of thyroid hormones. The longer the patients had been taking Sunitinib, the greater their risk of hypothyroidism.

Based on these findings, the scientists concluded that cancer treatment with Sunitinib can, in fact, cause a drop in blood thyroid hormone levels. In some cases, this reduction is severe enough to induce full-blown hypothyroidism.

Growth Hormone Therapy Can Cause Hypothyroidism

For patients with pituitary gland disorders, doctors often prescribe a treatment regimen that involves growth hormone. Similar treatments are also used in the care of patients with certain types of brain tumors.

However, according the results of a study recent published in the journal Clinical Endocrinology, this treatment can impede proper thyroid function and, in some cases, even cause hypothyroidism.

In the study, a sample of 243 patients on growth hormone therapy was studied throughout the course of the treatment. Although thyroid hormone levels varied according to the type of disorder each patient was being treated for, the scientists found an overarching trend of low serum thyroxine levels. Based on the findings, the authors concluded that the growth hormone treatment can be blamed for causing hypothyroidism by suppressing proper TSH secretion.  

 Cancer Drug Bexarotene Found to Interfere with Thyroid Hormone Secretion

Used primarily as a form of treatment for patients diagnosed with cutaneous T-call lymphoma, the drug Bexarotene has been associated in the past with diminished thyroid function. The results of a study recently published in the prestigious Journal of Clinical Endocrinology & Metabolism seem not only to bear this suspicion out, but also to pinpoint the source of the problem.

The study was conducted on a group of six normal, disease-free patients with no history of either lymphoma or thyroid dysfunction. In a series of overnight tests, the patients were given either Bexarotene or a placebo. After a waiting period, the subjects were then given a number of diagnostic procedures, including assessments of thyroid hormone levels in the bloodstream.

It was found that the patients who had been administered Bexarotene experienced a decline in several types of thyroid hormones. Low serum thyrotropin were most significantly affected. The authors noted that these findings were consistent with the documented risk of hypothyroidism that had previously been linked to Bexarotene treatment, and they concluded that the drug can inhibit TSH secretion.

If you’re worried about possible drug interactions and their impact on thyroid health, be sure to share your concerns with your physician. Don’t forget to check back each week for more breaking thyroid health and research news.