Thyroid drug needs FDA approval after decades of use

Jul 26 (HeartCenterOnline) - Manufacturers of the number one selling thyroid hormone replacement medication have been given until August 14 to submit the drug for FDA approval, despite the fact that the product called Synthroid has been marketed in the United States for 46 years. According to an article published July 24, 2001 in New York Times, both the FDA and manufacturers Abbott Laboratories assured the public that Synthroid was safe and patients on the medication should not stop taking it abruptly as the result of this FDA action.

Synthroid is a synthetic form of the hormone produced in the body's thyroid gland, a butterfly-shaped gland located at the base of the neck in front of the windpipe (trachea). The thyroid gland produces hormones that influence many different functions of the body, such as metabolism, growth and development, organ function, fertility and body temperature.

Thyroid disorders can lead to either too much thyroid hormone (hyperthyroidism) or not enough thyroid hormone (hypothyroidism) in the blood. Both hyperthyroidism and hypothyroidism have been associated with heart problems when left untreated. Hypothyroidism is far more common than hyperthyroidism and medications like Synthroid are the only known treatment for hypothyroidism.

Maintaining an appropriate dose of replacement thyroid hormones is a challenge for patients with hypothyroidism (under-active thyroid). Doses that are too low can cause a recurrence of hypothyroidism symptoms, including fatigue, weakness, muscle pain, thinning hair, memory loss, weight gain and depression. Doses that are too high can create symptoms usually associated with hyperthyroidism (over- active thyroid), including palpitations, anxiety, unusual sweating, feeling hot or flushed, trouble sleeping, vision changes or weight loss. This sensitivity to doses of thyroid hormones is one reason why it is so important that thyroid replacement drugs to not vary in potency from batch to batch.

According to the New York Times article, thyroid replacement medications were available before the FDA testing and approval process was created and therefore were grandfathered in. In 1997, the FDA announced a new policy regarding thyroid hormones and required manufacturers to submit their medications for FDA approval. Clinical trials were not required, however, manufacturers were required to prove to the FDA that they could make thyroid medications with consistent potency that would last for at least six months. According to the New York Times article, Abbott Industries is planning to meet the Aug. 14 deadline. Two other brands of thyroid drugs have since completed the FDA approval process while a third is pending approval.

More information on thyroid disorders can be found in the following HeartCenterOnline topic centers and encyclopedia articles:
Hypothyroidism
Heart-Threatening Illnesses