Levo-T (levothyroxine sodium)
The following drug information is obtained from various newswires, published
medical journal articles, and medical conference presentations.
Levo-T (levothyroxine sodium) has been approved by the FDA for
the treatment of hypothyroidism and the suppression of thyroid
stimulating hormone. Levo-T will be available in dosages ranging
from 25 mcg to 300 mcg.
Mechanism of Action
Synthetic levothyroxine (T4) is identical to that
produced naturally in the human thyroid gland. Thyroid hormone
synthesis and secretion is regulated by the
hypothalamic-pituitarythyroid axis. Thyrotropin-releasing hormone
(TRH) released from the hypothalamus stimulates secretion of
thyroid-stimulating hormone, TSH, from the anterior pituitary. TSH,
in turn, is the physiologic stimulus for the synthesis and
secretion of thyroid hormones, L-thyroxine (T4) and
L-triiodothyronine (T3), by the thyroid gland.
Circulating serum T3 and T4 levels exert a
feedback effect on both TRH and TSH secretion. When serum
T3 and T4 levels increase, TRH and TSH
secretion decrease. When thyroid hormone levels decrease, TRH and
TSH secretion increase.
In July 2001, the FDA announced that it would require all
manufacturers of levothyroxine sodium products to submit New Drug
Applications for approval of these products. This guidline applies
to both original and generic forms of the levothyroxine sodium
drugs. As of March 2002, Levo-T was the only generic levothyroxine
sodium product to be approved by the FDA.