A Study of T3 Therapy in Patients With Hypothyroidism

The purpose of this study is to test a new thyroid hormone preparation. The thyroid gland
produces two thyroid hormones: mostly T4 and a smaller amount of T3. Thyroid hormone therapy
for hypothyroidism or thyroid cancer is generally provided using levothyroxine, which is a
synthetic form of T4. T4 is converted into the active hormone T3 in the circulation.
Therefore, some researchers believe that T3 levels in T4-treated patients may be slightly
lower than in individuals whose own thyroid gland is functioning normally. Symptoms of
hypothyroidism have been suggested to occur because of this possible T3 deficiency, although
this is controversial. Studies of T3, added to or substituted for T4 in traditional
levothyroxine regimens, have generally not shown any benefit of T3. However, it is still
possible that no benefit is seen because of the short duration of action or "half-life" of
T3. This short-life makes it necessary to dose T3 twice or three times daily. Despite
multiple daily doses of T3, T3 levels during its therapy tend to be troubled by peaks and
troughs. These peaks can be associated with symptoms of excessive thyroid hormone levels.
This study will look at TSH and thyroid hormone levels following a daily dose of a new
preparation of T3 that may have longer duration of action than liothyronine. This
preparation of T3 is called Thyromax® or BCT303. The investigators believe that steady
levels of T3 will be seen after taking Thyromax®. The investigators believe that in patients
with hypothyroidism use of Thyromax® in the correct dose will produce normal TSH levels,
without producing symptoms of too much thyroid hormone. The goal of future studies is to
test whether Thyromax® may be a potential treatment for hypothyroidism, by comparing it with
traditional levothyroxine therapy.