Thormon

Generic

Levothyroxine Sodium

 

Indications

• As a replacement therapy for hypothyroidism caused by any cause. During the healing period of subacute Thyroiditis, replacement medication should not be started for transitory hypothyroidism.
• In the presence of goitres, nodules, and following radiological and/or surgical therapy of Thyroid cancer, to lower Thyroid Stimulating Hormone (TSH) levels.
• For the suppression of other medications' goitrogenic effects, such as lithium.
• In suppression testing as a diagnostic help.

 

Pharmacology

This tablet contains synthetic levothyroxine (also called thyroxine or T4), which is the same as the natural hormone T4 produced by the thyroid gland. Approximately 30% of T4 is converted into the more active triiodothyronine (T3) in peripheral tissues. TBG (thyroxine binding globulin) is the main carrier of T4. This combination protects T4 from the effects of metabolism and excretion, which leads to a longer circulatory half-life. Only about 0.03% of T4 in plasma is unbound. The elimination half-life of T4 is 6 to 7 days. The half-life of hyperthyroidism is shortened to 3 or 4 days, while the half-life of hypothyroidism may be 9 to 10 days. In cases related to a decrease in plasma protein, such as kidney disease or liver cirrhosis, or when protein binding is inhibited by certain drugs, the half-life of T4 may be shortened. The liver is the main place where thyroid hormones are broken down. T4 combines with glucuronic acid and sulfate through phenolic hydroxyl group and is excreted in urine. Enterohepatic circulation of thyroid hormones occurs because they are released and absorbed by hydrolysis in the intestine. Due to the long half-life of T4, a constant blood level of T3 with higher biological activity can be achieved by taking levothyroxine once a day. Therefore, once the correct dosage is determined, the therapeutic effect is unlikely to change.

 

Dosage & Administration

Adult dose:

• Initial starting dose: 25-50 meg/day, with gradual increments in dose at 6-8 week intervals, as needed. The Levothyroxine Sodium dose is generally adjusted in 12.5-25 meg increments until the patient with primary hypothyroidism is clinically euthyroid and the serum TSH has normalized.
• In patients with severe hypothyroidism: Initial dose is 12.5-25 meg/day with increases of 25 meg/day every 2-4 weeks, accompanied by clinical and laboratory assessment,until the TSH level is normalized.
• In patients with secondary (pituitary) or tertiary (hypothalamic) hypothyroidism: Levothyroxine Sodium dose should be titrated until the patient is clinically euthyroid and the serum free - T4 level is restored to the upper half of the normal range.
• For patients older than 50 years or for patients under 50 years of age with underlying cardiac disease: 1.7 meg/kg/day.

Pediatric Dosage (Newborns): The recommended starting dose is 10-15 meg/kg/day. A lower starting dose should be considered in infants at risk for cardiac failure and the dose should be increased in 4-6 weeks as needed based on clinical and laboratory response to treatment. In infants with very low (<5 mcg/dL) or undetectable serum T4 concentrations, the recommended initial starting dose is 50 meg/day of Levothyroxine Sodium.

Pediatric Dosage (Infants and Children): In children with chronic or severe hypothyroidism, initial dose of 25 meg/day with increments of 25 meg every 2-4 weeks until the desired effect is achieved. Hyperactivity in an older child can be minimized if the starting dose is one-fourth of the recommended full replacement dose and the dose is then increased on a weekly basis by an amount equal to one-fourth the full recommended replacement dose until the full recommended replacement dose is reached.

• 0-3 months: 10-15 meg/kg/day
• 3-6 months: 8-10 meg/kg/day
• 6-12 months: 6-8 meg/kg/day
• 1-5 years: 5-6 meg/kg/day
• 6-12 years: 4-5 meg/kg/day
• >12 years but growth and puberty incomplete: 2-3 meg/kg/day
• Growth and puberty complete: 1.7 meg/kg/day.

The dose should be adjusted based on clinical response and laboratory parameters.

 

Interaction

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.

 

Contraindications

• Any etiology of untreated subclinical or overt thyrotoxicosis
• Adrenal insufficiency due to uncorrected acute myocardial infarction.

 

Side Effects

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

• Fatigue, increased appetite, weight loss, heat sensitivity, fever, and heavy perspiration are all symptoms of heat intolerance.
• Headache, hyperactivity, nervousness, anxiety, irritability, emotional lability, and insomnia are all symptoms of the central nervous system.
• Tremors and muscle weakness are musculoskeletal symptoms.
• Palpitations, tachycardia, arrhythmias, elevated pulse and blood pressure are all symptoms of cardiovascular disease.
• Dyspnea is a respiratory condition.
• Diarrhea, vomiting, and stomach cramps are all symptoms of gastrointestinal problems.
• Hair loss and flushing are two dermatological symptoms.

 

Pregnancy & Lactation

Category A Pregnancy. The need for Levothyroxine may increase during pregnancy. Although thyroid hormones are excreted in small amounts in human milk, caution should be maintained when given to a nursing mother. To maintain regular lactation, however, appropriate replacement doses of Levothyroxine are usually required.

 

Precautions & Warnings

• Patients with hypothyroidism caused by hypopituitarism may also have adrenal insufficiency; before starting levothyroxine therapy, treatment should be adequately substituted for corticosteroids to prevent acute adrenal insufficiency.
• For patients with cardiovascular disease and/or severe and long-term hypothyroidism, the starting dose and increasing dose should be carefully selected. A too high starting dose or a too fast dose increase can lead to the development or worsening of angina symptoms, arrhythmia, myocardial infarction, heart failure, or sudden increase in blood pressure, especially in the elderly.
• Any significant change in body weight during treatment with T4 requires a dose adjustment.
• When monitoring T3 and T4 blood levels, it should be noted that to achieve normal T3 levels, a "high" normal to slightly elevated T4 level is required. The correct dose of levothyroxine in patients with primary hypothyroidism should generally be determined by monitoring the serum TSH level to see if it has returned to normal. Because poisoning of thyroid preparations can have serious consequences.

 

Therapeutic Class

Thyroid drugs & hormone

 

Storage Conditions

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

 

Pharmaceutical Name

Aristopharma Ltd.