liothyronine and levothyroxine sodium

Levothyroxine Sodium – a synthetic form of a natural thyroid hormone tetraiodothyronine (T4).

Thyroid hormones are responsible for regulating the rate of metabolism in the body and plays a vital role in the assimilation of proteins, fats and carbohydrates. Levothyroxine sodium is used in medicine for the treatment of hypothyroidism, a disease characterized by insufficient levels of the natural thyroid hormone. The disease has a number of symptoms that include loss of energy, lethargy, weight gain, hair loss and changes in skin texture.

Levothyroxine sodium is considered to be slow-acting drug, and to achieve the full therapeutic effect may require 4-6 weeks. The drug is most commonly prescribed treatment for thyroid in the world and is considered a standard treatment for most cases of hypothyroidism.

In small doses has anabolic effects, in the medium – it stimulates growth and development, increases tissue oxygen demand, regulates the metabolism of proteins, fats and carbohydrates, increases the functional activity of the cardiovascular system and central nervous system, in large – inhibits the production of thyrotropin-releasing hormone from the hypothalamus and pituitary thyroid stimulating hormone.

Effect of sodium levothyroxine is very close to the action of a popular drug for thyroid Cytomel (liothyronine sodium). Cytomel has a slightly different structure, and is a synthetic form of thyroid hormones triiodothyronine (T3).

In healthy humans contains sufficient levels of the hormones T3 and T4 thyroid. T3 is considered a major active form of thyroid hormone while T4 serves mainly as a backup to T3, showing most of its metabolic activity through conversion to T3 in peripheral tissues. It is believed that T3 is about four times more efficient than T4 in comparison milligram per milligram. Furthermore, Cytomel considered more effective form of treatment for thyroid, both in its activity, and with respect to side effects.

Levothyroxine sodium is used by many athletes and bodybuilders for its ability to stimulate the metabolism and support the disintegration of fat stores in the body. The drug is usually taken under the restriction of calories ( “drying”), when the user is interested in losing fat or increase muscle relief. It is expected that the use of thyroid drugs may promote fat loss at a higher level of calorie intake than would be possible without the use of such drugs.

Together with these hormones are commonly used anabolic steroids, and many believe that the improvement in metabolism caused by these drugs, may produce rapid muscle growth. However, until now no drug’s effectiveness has been proven in this respect.

Medical use Thyroxine

hypothyroid state of various etiologies (including those due to surgical or medical exposure), prevention of recurrence after resection of nodular goiter thyroid, diffuse euthyroid goiter; diffuse toxic goiter – after creating tireostatikami euthyroid state (as monotherapy or combined); thyroid cancer after surgery (for the purpose of suppressing and tumor recurrence as replacement therapy), as a diagnostic tool for the test thyroid suppression. In the combined therapy: Graves’ disease, Hashimoto’s thyroiditis.


Levothyroxine – the first commercial synthetic drug for the treatment of thyroid cancer in the US, which was first introduced on the market in 1955 under the name Synthroid from Flint Laboratories.

The drug has a long history of therapeutic use in the US and internationally, and for decades has been the most widely used drug for the treatment of hypothyroidism. The figures show that Synthroid brand provided 85% of total sales of levothyroxine and revenues from sales of the drug amounted to $ 600 million.

In the community of bodybuilders and athletes more and more popular, however, uses a faster and more powerful medication Cytomel (liothyronine). Since Synthroid is considered to be a weaker drug in slow motion, in order to achieve similar results have to make it last longer.

Synthroid brand itself has a long and complex history. A few years after its creation, Synthroid has gained a monopoly on the market of levothyroxine sodium products. In the 1980s, however, begin to appear generic levothyroxine sodium. In response to this, in 1986, the company Flint is funding research at the University of California. This was done in order to demonstrate that Synthroid has a greater therapeutic value than its generic versions. The study was completed in 1990, and, in fact, proved that generic drugs have equal efficacy with Synthroid.

The contract was a clause that the publication of this study need to get approval from the company Flint. Began litigation for publication. Even after Flint Laboratory was sold to Boots, which was then sold to Knoll, the publication of studies constantly postponed. In the end, a study was published in 1997. This was followed by a class action lawsuit, which alleged that a lack of information, consumers forced to pay 2-3 times only for the brand drug. Ultimately Knoll company agreed to pay $ 135 000 000

Product form

Levothyroxine sodium is most often comes in the form of oral tablets of 25, 50, 75, 100, 125, 150, 200 and 300 micrograms.

Drug interactions

decreases the effect of insulin and of oral antidiabetic drugs, cardiac glycosides, amplifies – anticoagulants, tricyclic antidepressants. Alter protein binding anabolic steroids, asparaginase, clofibrate, furosemide, salicylates, tamoxifen. Amiodarone, aminoglutethimide, aminosalicylic acid, ethionamide, antithyroid drugs, beta-blockers, carbamazepine, chloral hydrate, diazepam, levodopa, dopamine, metoclopramide, lovastatin, somatostatin et al. Can alter the levels of thyroid and thyroid-stimulating hormone, usually affecting the synthesis, secretion , distribution, metabolism, elimination or action of thyroid hormones or altering the secretion of TSH.

Some foods and other substances can also affect the absorption of thyroxine replacement. Patients should avoid taking calcium and iron for 4 hours and also soy products within 3 hours after drug application, as this can reduce the absorption of the drug.

Grapefruit juice may delay the absorption of levothyroxine, but he did not have a significant effect on the bioavailability of the substance. Other substances that reduce the absorption of L-Thyroxine include antacids containing aluminum and magnesium, simethicone or sucralfate, cholestyramine, colestipol, Kayexalate.

Study, including eight women, it showed that the intestinal absorption of levothyroxine may also affect coffee, although to a lesser extent than bran.

Various substances can cause other side effects that can be severe. Ketamine can lead to hypertension and tachycardia, and tricyclic and tetracyclic antidepressants – to increase the toxicity of the substance. On the other hand, lithium can cause hyperthyroidism (but often hypothyroidism), affecting the metabolism of iodine in the thyroid gland itself and hence inhibiting synthetic levothyroxine.

Side effects

Side effects are usually related to overdose, and may include headache, irritability, nervousness, sweating, irregular heartbeat, increased bowel motility, or menstrual irregularities. Overdosing can also cause shock and also aggravate or cause angina or congestive heart failure.

Chronic overdose of sodium levothyroxine causes symptoms commonly associated with hyperthyroidism natural or overproduction of thyroid hormones in the body. If you experience these side effects, the dosage should be reduced immediately or completely stop taking levothyroxine sodium. Acute overdose can be life-threatening.

Update on the preparations of thyroxine contains a warning about the influence of thyroxin on bone mineral density. Patients receiving treatment with thyroxine, it is recommended to apply it in the minimum doses needed to achieve the desired clinical and biochemical response.

Besides increasing the risk of osteoporosis, excess thyroxine can also increase the risk of arrhythmias, muscle weakness in all patients, but especially in the elderly.


For the treatment of hypothyroidism from mild to moderate, average substitution dose of levothyroxine sodium is about 1.7 .mu.g / kg / day, i.e. 100-125 mg / day for an adult human being weighing 70 kg.

At the beginning of therapy and full therapeutic dose can be used, provided that the patient has no other disease. It should be noted that, due to the long half-life of levothyroxine peak therapeutic effect for a given dosage is reached after 4-6 weeks of application.

By using (non-label) for accelerating fat burning process in athletes and body builders, so that the body has had enough time to adapt to the changing levels of thyroid hormone, the dosage is usually increased gradually. The drug usually starts with a low dose of 25-50 mg, and gradually increases to 25-50 mg every two-three days. The ultimate dosage is typically in the range 100-150 mg, and rarely more than 250 micrograms.

It is important to remember that the preparations for the thyroid gland are very strong drugs and have significant potential side effects. In order to care is not recommended to use levothyroxine sodium in high doses and for longer than eight weeks.

Course Duration 4-7 weeks. Do not stop taking thyroxine sharply, begin to reduce the dose for 2 weeks before the end of the cycle, continues to gradually decline to complete abolition. Typically, dosage is decreased to 25 micrograms every second or third day. This is done in order to avoid sudden changes in hormone levels, which, otherwise, could cause adverse side effects. It should be noted that, due to slow action of levothyroxine sodium, a complete excretion of the drug may take several weeks or longer.

The most striking manifestation of side effects (tachycardia, increased pressure) stoped metoprolol or decrease levothyroxine dosage.

Minimum break with levothyroxine courses must not be less than 4-6 weeks.

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