Levothyroxine is considered the gold standard therapy for an underactive thyroid gland (hypothyroidism), and a new review of therapies for the condition, which included combining levothyroxine with another agent, has not altered that assessment, said a team of investigators. Their analysis, published as a set of guidelines, found insufficient consistent data exist to recommend a change in use of levothyroxine as the only drug needed to treat hypothyroidism.
“Levothyroxine has been seen as a miracle drug that reverses symptoms of hypothyroidism in most individuals,” says the guidelines study lead author Jacqueline Jonklaas, MD, PhD, an associate professor at Georgetown University Medical Center and a specialist in treating thyroid diseases at MedStar Georgetown University Hospital in Washington, DC. The guidelines were published in the journal Thyroid (2014; doi:10.1089/thy.2014.0028).
The American Thyroid Association asked Jonklaas and 10 other researchers from three countries to review existing data and prepare the new hypothyroidism treatment guidelines. Jonklaas served as clinical chair of the task force.
Hypothyroidism is common and is believed to affect up to 5% of the American population, with most being middle-age women, according to Jonklaas. In the US population, the disorder stems from an errant autoimmune response, but worldwide it is more likely to be due to iodine deficiency, she said.
Levothyroxine, developed in the 1950s, has been thoroughly tested and found to be very effective, Jonklaas said. Proper functioning of the thyroid involves two hormones, thyroxine (T4), and triiodothyronine (T3). Levothyroxine is a synthetic form of T4, which is then converted to T3 inside the body. Levothyroxine comes in generic versions and is sold under various trade names, such as Synthroid.
But because some patients have felt that the drug did not completely restore their health, a synthetic T3 preparation, already developed and has been approved, is sometimes added to levothyroxine. Unlike levothyroxine, this T3 agent must be taken more than once a day.
The guidelines considered the preclinical and clinical evidence backing use of a T3 agent in combination with levothyroxine and found the data to be insufficient. “The studies were performed in many different ways, had some inconsistent findings, and none looked at use of a T3 agent for an extended period, which is necessary in order to uncover side effects,” Jonklaas said. “Given that additional studies are needed, the task force did not feel that combination therapy should be recommended for routine use.
“All in all, our guidelines offer reassurance to physicians and their patients,” she said. “No changes are needed in the current standard of care for hypothyroidism in the majority of patients.”