Novothyrox (levothyroxine sodium) is a thyroid hormone replacement drug to treat Hypothyroidism and suppression of thyroid-stimulating hormone. Novothyrox is a tablet administered as a once-daily therapy. The dose necessary to achieve normal thyroid hormone levels is dependent on several factors, including, but not limited to the patient's age, weight, and cardiovascular status, as well as the nature of the condition being treated. The average full replacement dose of levothyroxine is approximately 1.7 mcg/kg/day.

Adverse reactions associated with levothyroxine therapy are usually symptoms of hyperthyroidism due to therapeutic overdosage.

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 thyrotropin-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. (From Novothyrox prescription label)

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.

For more information about this FDA ruling, please refer to the guidance itself on the FDA web site at www.fda.gov/cder/guidance/4647fnl.htm.