Thyrox

This tablet contains synthetic Levothyroxine (also called Thyroxine or T4) which is identical to the natural hormone T4, produced in the Thyroid gland. About 30% of T4 is converted to the much more active Triiodothyronine (T3) in peripheral tissues. TBG (Thyroxine 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% 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 Levothyroxine. Therefore, variations in the therapeutic effect are unlikely once the correct dosage has been established.

Concurrent use of tri/tetracyclic antidepressants and Levothyroxine may increase the therapeutic and toxic effects of both drugs, possibly due to increased receptor sensitivity to catecholamines.Toxic effects may include increased risk of cardiac arrhythmias and CNS stimulation; onset of action of tricyclics may be accelerated. Administration of sertraline in patients stabilized on Levothyroxine may result in increased Levothyroxine requirements. Addition of Levothyroxine to antidiabetic or insulin therapy may result in increased antidiabetic agent or insulin requirements. Careful monitoring of diabetic control is recommended, especially when thyroid therapy is started, changed, or discontinued. Serum digitalis glycoside levels may be reduced in hyperthyroidism or when the hypothyroid patient is converted to the euthyroid state. Therapeutic effect of digitalis glycosides may be reduced.

Adverse reactions associated with Levothyroxine therapy are primarily those of hyperthyroidism due to therapeutic overdose. They include the following:

• General: Fatigue, increased appetite, weight loss, heat intolerance, fever, excessive sweating;
• Central nervous system: Headache, hyperactivity, nervousness, anxiety, irritability, emotional lability, insomnia.
• Musculoskeletal: Tremors, muscle weakness.
• Cardiovascular: Palpitations, tachycardia, arrhythmias, increased pulse and blood pressure
• Respiratory: Dyspnea.
• Gastrointestinal: Diarrhea, vomiting, abdominal cramps.
• Dermatologic: Hair loss, flushing.

Pregnancy Category A. Pregnancy may increase Levothyroxine requirements. Although Thyroid hormones are excreted only minimally in human milk,caution should be exercised when it is administered to a nursing woman.However, adequate replacement doses of Levothyroxine are generally needed to maintain normal lactation.

• In patients whose hypothyroidism is due to a decrease in pituitary gland function, there may also be adrenocortical insufficiency;before starting Levothyroxine therapy, this should be treated by adequate replacement with Corticosteroids to prevent acute adrenal insufficiency.
• The choice of the starting dose and of any increases in dosing should be made with great care in patients with cardiovascular disease and/or severe and long-existing hypothyroidism.Too high an initial dose or too rapid an increase in dosing may lead to development or worsening of angina complaints, arrhythmias, myocardial infarction, cardiac failure or to sudden increase in blood pressure, especially in older patients.
• Any marked change of body weight during treatment with T4 requires adjustment of the dosage.
• When monitoring blood levels of T3 and T4, it should be borne in mind that a “high” normal to slightly increased T4 level will be necessary in order to obtain a normal level of T3. The correct dosage of Levothyroxine in primary hypothyroidism should generally be established by monitoring the serum level of TSH to see whether it has normalized. Because intoxication with Thyroid preparations may have serious consequences.

Thyroid drugs & hormone

The signs and symptoms of overdose are those of hyperthyroidism – agitation, confusion, irritability, hyperactivity, headache, sweating, mydriasis, tachycardia, arrhythmias, tachypnoea, pyrexia, increased bowel movements and convulsions. Cerebral embolism, shock, coma, and death have been reported. Symptoms may not necessarily be evident or may not appear until several days after ingestion of Levothyroxine Sodium. Dose of Levothyroxine Sodium should be reduced or temporarily discontinued if signs or symptoms of overdosage occur. Treatment is symptomatic.

Store below 30°C and dry place, protect from light. Keep out of the reach of children.