BACKGROUND
Hypothyroidism, or underactive thyroid, is diagnosed with a higher TSH and low or low-normal FT4. Common symptoms include feeling tired, cold, constipated, gaining weights and having dry skin. Hypothyroidism is most often treated with levothyroxine, which is the main hormone that the normal thyroid makes (T4). Levothyroxine is then converted in the body, to the active thyroid hormone, triiodothyronine (T3).

Another thyroid hormone preparation is desiccated thyroid extract (DTE), which was the main treatment for hypothyroidism before levothyroxine was isolated and purified in the 1960s. DTE has both forms of thyroid hormone as it is made by ground up thyroids from either cows or pigs. As such, it contains both T4 and T3. Some practitioners and some patients prefer DTE because of it containing bother thyroid hormones. Further, some patients that do not feel well on levothyroxine alone do better on DTE.

A third thyroid hormone preparation is T3, or liothyronine. This is usually used along with levothyroxine (T4/ T3 therapy).

This study reviewed clinical prescriptions databases regarding prescriptions for levothyroxine and desiccated thyroid extract to understand the frequency of prescriptions of these forms of thyroid hormone replacement.

THE FULL ARTICLE TITLE
Ettleson MD et al 2023 Demographic, healthcare access, and dietary factors associated with thyroid hormone treatments for hypothyroidism. J Clin Endocrinol Metab. Epub 2023 Jun 16. PMID: 37327351.

SUMMARY OF THE STUDY
This study reviewed two databases for thyroid hormone prescriptions. Data was reviewed for those patients who had received at least one new thyroid hormone prescription for a diagnosis of hypothyroidism. The years of study were 1996 to 2020 among the two databases. A total of 524,818 patients were included. The average age was 50.8 years, and 72.1% were women.

On an average annual basis, there were 47,711 adults who received at least 1 new thyroid hormone prescription— 88.3% levothyroxine, 2.0% liothyronine, and 9.4% DTE therapy. The proportion of newly prescribed DTE therapy increased from 5.4% in 2010 to 10.2% in 2020. New liothyronine prescriptions remained relatively stable between the two periods—2.4% in 2010 and 2.2% in 2020. Regions with many PCP and endocrinology physicians were associated with increased use of levothyroxine. The proportion of DTE or liothyronine use was higher in the West and Southwest U.S. regions than in the North and upper Midwest regions. Liothyronine and DTE therapies were more common in patients living in large metropolitan zones than in those living in rural zones Conversely, levothyroxine was less likely to be prescribed in metropolitan zones than in in rural zones.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
The study showed that the prescriptions for desiccated thyroid extract have doubled between the years 2010 and 2020. There has been a notable increase in the percentage of prescriptions for DTE. Even though it averages to about 10% of the total prescriptions of thyroid hormone, the use has increased, especially in areas with a low number of physicians and large metropolitan areas. It would be important to educate patients on the differences between various thyroid hormone preparations so they can make an informed decision. Understanding the risks such as side effects versus benefits of the DTE preparations is important as well.

— Vibhavasu Sharma,MD,FACE

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