The appearance and traits of levothyroxine are beige powder. Levothyroxine can be absorbed by the gastrointestinal tract, but the absorption is incomplete and the absorption rate is uncertain, especially when it is taken with food. After T4 is absorbed into the blood, most of it binds to plasma proteins, only about 0.03% exist in free form, about 80% binds to thyroxine-binding globulin, and a small amount binds to thyroxine-binding protein or albumin.
Sodium levothyroxine is the sodium salt of levothyroxine. Levothyroxine, also known as synthetic T4 or '3,5,3',5'-tetraiodo-L-thyroxine is a synthetic form of thyroxine (thyroid hormone) for patients with thyroid disorders Hormone replacement therapy. Natural thyroid hormones are chemically structurally chiral-L-configuration as in the pharmaceutical formulation. D-thyroxine has been studied as an anticholesterol drug. However, it was cancelled because of the side effects of the heart.