Each tablet contains Levothyroxine Sodium USP 50mcg
THYRONOR™ contains synthetic levothyroxine (also called thyroxin or T4) which is identical to the natural hormone T4, produced in the thyroid gland. About 30 per cent of T4 is converted to the much more active triiodothyronine (T3) in peripheral tissues. TBG (thyroxin-binding globulin) is the major carrier of T4. This binding protects T4 from metabolism and excretion resulting in its long half-life in the circulation. Only about 0.03 per cent of total T4 in plasma is unbound. The half-life of elimination of T4 is 6 to 7 days. In hyperthyroidism, the half-life is shortened to 3 or 4 days, whereas in hypothyroidism it may be 9 to 10 days. In conditions associated with reduced protein in plasma as in nephrosis or hepatic cirrhosis, or when binding to protein is inhibited by certain drugs the half-life of T4 may be shortened. The liver is the major site of degradation of thyroid hormones. T4 is conjugated with glucuronic and sulphate conjugates through the phenolic hydroxyl group and excreted in the urine. There is an enterohepatic circulation of the thyroid hormones, since they are liberated by hydrolysis in the intestine and reabsorbed. Because of the long half-life of T4 a steady blood level of the biologically more active T3 can be obtained from one single daily dose of THYRONOR™. Therefore, variations in the therapeutic effect are unlikely once the correct dosage has been established.
- As replacement therapy in hypothyroidism of any etiology.
- For the suppression of Thyroid Stimulating Hormone (TSH) levels in the presence of goiters, nodules and after radiological and/or surgical treatment of thyroid cancer.
- For the suppression of the goitrogenic effects of other drugs such as lithium.
- As a diagnostic aid in suppression tests.
It is not known whether T4 affects lactation. T4 is excreted in small quantities in breast milk, but it is unlikely that these affect the infant when therapeutic doses are used.
Too high a dosage may lead to symptoms of hyperthyroidism such as
- Loss of weight
Acute over dosage with thyroid preparations may lead to a thyrotoxic crisis.
Detail prescribing information: