Levothyroxine

Levothyroxine, also known as levothyroxine sodium, is a medication used to replace the thyroid hormone thyroxine. It is one of the most frequently prescribed drugs in the world and is used to treat patients whose thyroids do not produce the correct amount of thyroxine. Levothyroxine is the primary treatment for patients with hypothyroidism, a condition in which the thyroid gland does not make enough hormone. It is also used to replace the natural hormone after the removal or destruction of the thyroid gland in patients who have had conditions such as thyroid cancer.

Background

The thyroid is a butterfly-shaped gland about two inches long that is located in the throat just below the Adam's apple. Its primary function is the production of thyroid hormones, or substances that regulate how cells use energy in the process of metabolism. Thyroid hormones are responsible for controlling breathing, heart rate, the nervous system, the reproductive cycle in women, muscle strength, cholesterol levels, body temperature, weight, and other key body functions. The body uses iodine from food sources to produce two types of thyroid hormone: triiodothyronine, also known as T3, and thyroxine, also known as T4.

The amounts of these hormones that are produced are controlled by other parts of the endocrine system, the hypothalamus and the pituitary gland. When something breaks down in the process and causes the body to produce too little T3 and T4, the patient will experience symptoms such as slow heart rate, poor digestion, irregular menstrual periods, and possible weight gain because there is not enough thyroid hormone circulating in the body to promote healthy function. On the other hand, when too much T3 and/or T4 is produced, these systems will work harder and faster than normal, causing symptoms such as a racing heart or diarrhea, light and infrequent periods, nervousness and hyperactivity, or the need to eat more to avoid weight loss. This is known as hyperthyroidism.

Medical practitioners have been aware of the effects of too much thyroid hormone for centuries. As far back as 2700 BCE, Chinese physicians were prescribing seaweed for the treatment of goiters, the swellings of the thyroid that happen in hyperthyroidism. The iodine in seaweed helped regulate the body's natural production of the hormone. Seaweed continued to be the treatment of choice for Chinese, Greek, and other ancient physicians until around 650 CE, when a Chinese physician named Sun Ssu-Mo recommended the use of mollusk shells that were dried and crushed to a powder as a treatment for goiters. He also treated the condition by giving patients dried and chopped thyroid glands from animals. Another Chinese physician, Wang Hei, endorse the use of minced thyroid glands to treat thyroid problems around 1475 CE. Others, including English physician George Murray, who used injections of sheep thyroid to treat a patient with hypothyroidism for more than thirty years beginning in 1891, would experiment with various ways to use animal thyroids to treat human patients.

On Christmas Eve 1914, a Mayo Clinic physician named Edward C. Kendall purified a new experimental batch of thyroid material extracted from a pig and left it to crystallize. When he returned to the laboratory the next day, he discovered he had created the first purified powdered thyroid crystals. The new compound was the first time the hormone itself was extracted from the thyroid. Within ten years, British chemist Charles Harington refined the process further. By 1949, levothyroxine was available to the public as a commercial prescription drug manufactured by the Glaxo Pharmaceutical Company, now known as GlaxoSmithKline.

Overview

Levothyroxine is sold in 50 and 100-microgram doses dispensed as either a tablet or a liquid-filled capsule under several brand names, including Levothroid, Levo-T, Levoxyl, Synthroid, Tirosint, and Unithroid. It is prescribed either for patients who have too little natural thyroid hormone—hypothyroidism—or for patients who have had their thyroids removed or destroyed by radiation, such as thyroid cancer patients and survivors. In either case, the oral medication replaces the hormone that should be produced by the body. Ingredients in levothyroxine include the active ingredient anhydrous levothyroxine sodium, lactose, magnesium stearate, maize starch, pregelatinised maize starch, and stearic acid.

Patients being treated for a thyroid condition will have blood tests before treatment with levothyroxine to determine the dosage needed. Once treatment begins, patients will require periodic blood tests to monitor the drug's effectiveness. Patients usually start with a 50-microgram dose and may end up at a dose of about 100 to 200 micrograms a day, taken with water on an empty stomach. Patients over fifty years of age may start with lower doses or take the medication every other day. Dosing is lower for children. Once a patient starts treatment with levothyroxine, it is generally continued for life.

There are some possible side effects from the medication. The most serious one would be an allergic reaction. This generally presents as swelling of the lips, tongue, throat, or face; difficulty breathing; and itching. An allergic reaction requires immediate medical attention. Patients can also develop problems if the dosage is too high or if too much medication is taken. A "thyroid crisis" is a severe reaction that causes an extremely high body temperature, a fast or irregular heartbeat, low blood pressure, and/or confusion. This potentially serious condition requires urgent medical treatment. Other less severe reactions can be caused by having too much of the drug in the patient's system. Symptoms of this include headaches, chest pains and irregular heart rates, high temperature, diarrhea and vomiting, restlessness and excitability, difficulty sleeping, and weight loss. These symptoms come on more gradually and require consultation with a physician to adjust the dosage of the levothyroxine.

Concerns

Some debate exists in the medical community and among thyroid patients about the relative merits of the use of levothyroxine versus the use of dried thyroid extract taken from the glands of pigs. Some patients claim to experience better results with fewer side effects when using the pig thyroid extract, marketed under the names Armour Thyroid and Nature-Throid. Some patients see these products, which are similar to those used before commercial synthetic levothyroxine was available, as being more natural and therefore preferable to laboratory created products. Laboratory studies where patients received a trial on one therapy followed by treatment on the other have revealed no differences in the clinical results.

Bibliography

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McAninch, Elizabeth. "A White Powder Obtained on Christmas Morning Used to Treat Hypothyroidism." Rush University Medical Center, 17 Dec. 2013, deiodinase.org/2013/12/17/a-century-old-white-powder-obtained-on-christmas-morning-is-still-used-to-treat-hypothyroidism/. Accessed 1 Dec. 2016.

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