Tyroid

Generic

Levothyroxine Sodium

 

Indications

• As a replacement treatment for hypothyroidism of any cause. Replacement treatment should not be started in patients with transitory hypothyroidism who are recovering from subacute thyroiditis.
• Thyroid Stimulating Hormone (TSH) suppression in the presence of goitres and nodules, as well as following radiological and/or surgical therapy of thyroid cancer.
• For the inhibition of other medicines' goitrogenic effects, such as lithium.
• In suppression testing, as a diagnostic tool.

 

Pharmacology

This pill includes synthetic Levothyroxine (commonly known as Thyroxine or T4), which is the same as the natural hormone T4, which is generated in the thyroid gland. In peripheral tissues, approximately 30% of T4 is transformed to the considerably more active Triiodothyronine (T3). TBG (Thyroxine Binding Globulin) is the primary T4 carrier. Because of this binding, T4 is protected from metabolism and elimination, resulting in a lengthy half-life in the circulation. Unbound T4 accounts for just around 0.03 percent of total T4 in plasma. T4 elimination has a half-life of 6 to 7 days. The half-life in hyperthyroidism is 3 or 4 days, but in hypothyroidism it might be 9 to 10 days. T4 half-life may be decreased in situations associated with low protein in plasma, such as nephrosis or hepatic cirrhosis, or when binding to protein is blocked by specific medications. Thyroid hormones are mostly degraded in the liver. T4 is eliminated in the urine after being conjugated with Glucuronic and Sulphate conjugates through the Phenolic hydroxyl group. Thyroid hormones circulate via the enterohepatic system because they are hydrolyzed and reabsorbed in the gut. Because of T4's extended half-life, a single daily dosage of Levothyroxine can provide a consistent blood level of the physiologically more active T3. As a result, once the right dosage has been identified, changes in the therapeutic impact are uncommon.

 

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.

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. In the treatment of goitres, nodules and Thyroid cancer, the objective is to ensure a constant and sufficient suppression of TSH. For suppression of TSH levels, a gradual increase in dosing is usually not necessary. For adults, the usual suppressive dosage of T4 is 2.6 meg/kg of body weight daily. When Levothyroxine Sodium is used as a diagnostic aid, the dosage depends on the type of investigation.

 

Interaction

Concurrent use of thyroid hormones with any of the following medications or substances may result in clinically significant interactions:

• Thyroid hormones have been shown to increase the action of oral anticoagulants.
• Thyroid hormones may increase the need for insulin or oral hypoglycemic medications in diabetics.
• Thyroid hormones may modify the need for Digitalis preparations.
• Cholestyramine: Cholestyramine may reduce thyroid hormone absorption; thus, at least 4 hours should elapse between administrations.
• Phenytoin appears to improve thyroid hormone metabolism and may also displace T4 from TBG.
• Foods: To minimize uneven absorption, Levothyroxine pills should be taken on an empty stomach at a predetermined time. Food consumption at the same time may reduce T4 absorption.

 

Contraindications

Acute Myocardial Infarction, Uncorrected Adrenal Failure, Untreated Subclinical or Overt Thyrotoxicosis of Any Etiology.

 

Side Effects

A high dose may cause hyperthyroidism symptoms such as tachycardia, anxiety, tremor, headache, flushing, sweat, and weight loss. If required, therapy might be stopped for a few days and then restarted at a reduced dose.

 

Pregnancy & Lactation

Pregnancy Type A. Pregnancy may increase the need for Levothyroxine. Although thyroid hormones are relatively little excreted in human milk, care should be used when administering it to a breastfeeding mother. However, sufficient Levothyroxine replacement dosages are typically required to ensure normal lactation.

 

Precautions & Warnings

• In individuals whose hypothyroidism is caused by a reduction in pituitary gland function, there may also be adrenocortical insufficiency; this should be addressed before commencing Levothyroxine therapy by sufficient replacement with Corticosteroids to prevent acute adrenal insufficiency.
• In patients with cardiovascular illness and/or severe and long-standing hypothyroidism, the initial dose and any dose increases should be chosen with caution. Too high an initial dose or too quick an increase in dosing may result in the development or aggravation of angina symptoms, arrhythmias, myocardial infarction, cardiac failure, or a sudden rise in blood pressure, particularly in elderly individuals.
• Any significant change in body weight during T4 therapy necessitates dose modification.
• When monitoring T3 and T4 levels in the blood, keep in mind that a "high" normal to slightly raised T4 level is required to get a normal level of T3.
• In general, the optimal dosage of Levothyroxine in primary hypothyroidism should be determined by monitoring the blood TSH level to check if it has normalized.
• Because Thyroid preparation intoxication might have significant effects.

 

Therapeutic Class

Thyroid medications and hormones

 

Storage Conditions

Keep cool and dry, and keep away from direct sunlight. Keep out of children's reach.

 

Pharmaceutical Name

ACI Limited