Thyrin 50

Indications of Thyrin 50

Hypothyroidism - Primary (thyroidal), secondary (pituitary), and tertiary (hypothalamic) hypothyroidism and subclinical hypothyroidism.

2. Pituitary TSH Suppression

 

Pharmaceutical Name of Thyrin 50

Square Pharmaceuticals Ltd.

 

Pharmacolgy

Levothyroxine is a synthetic thyroid hormone, thyroxine (T4, a tetra-iodinated tyrosine derivative) that is made and released by the thyroid gland. In the liver and kidney, T4 is converted to T3, the active metabolite. In order to increase solubility, the thyroid hormones attach to thyroid hormone binding proteins, thyroxine-binding globulin, and thyroxine-binding prealbumin (transthyretin). Transport and binding to thyroid hormone receptors in the cytoplasm and nucleus then takes place. Thus by acting as a replacement for natural thyroxine, symptoms of thyroxine deficiency are relieved. 

 

Dosage & Administration

Dosing must be individualized and adjustments made based on periodic assessment of the patient’s clinical response and laboratory parameters.

 

1. a) Adult Dosage

Initial starting dose: 25-50 mcg/day, with gradual increments in dose at 6-8weekintervals, as needed. The dose is generally adjusted in 12.5-25 mcg increments until the patient with primary hypothyroidism is clinically euthyroid and the serum TSH has normalized.

In patients with severe hypothyroidism: 12.5-25 mcg/day with gradual increment of 25 mcg/ day every 2-4 weeks.

In patients with secondary (pituitary) or tertiary (hypothalamic) hypothyroidism: The 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 mcg/kg/day.

 

1. b) Pediatric Dosage

Newborns

The recommended starting dose is 10-15 mcg/kg/day. In infants with very low (< 5 mcg/dL) or undetectable serumT4 concentrations, the recommended initial starting dose is 50 mcg/day.

Infants and Children

Initial dose is 25 mcg/day with increments of 25 mcg every 2-4 weeks until the desired effect is achieved.

 

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

Untreated subclinical or overt thyrotoxicosis of any etiology and acute myocardial infarction.

 

Side Effects

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 & Lactation

Pregnancy - Category A. Pregnancy may increase Levothyroxine requirements.

Nursing Mother - 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. 

 

Precautions & Warnings

Levothyroxine has a narrow therapeutic index. So, careful dosage titration is necessary to avoid the consequences of over- or under-treatment. Caution is needed when administering Levothyroxine to patients with cardiovascular disorders, to the elderly in whom there is an increased risk of occult cardiac disease & for patients with nontoxic diffuse goiter or nodular thyroid disease in order to prevent precipitation of thyrotoxicosis.

 

Therapeutic Class

Thyroid drugs & hormone.

 

Storage Conditions

Store in a cool and dry place, protect from light. Keep out of the reach of children.

 

Generic Name of Thyrin 50

Levothyroxine Sodium

 

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