Hypothyroidism - Medications

Medications:

Thyroid Hormone Replacement

The goal of thyroid drug therapy is to provide the body with replacement thyroid hormone when the gland is not able to produce enough itself.

A synthetic thyroid hormone called levothyroxine is the treatment of choice for hypothyroidism. This drug is a synthetic derivative of T4 (thyroxine), and it normalizes blood levels of TSH, T4, and T3.

Brand Names. A number of levothyroxine brands are available. Synthroid is the oldest brand and has been used for over 40 years. In the past, manufacturers of levothyroxine did not need to meet as strict standards as in the production of other drugs. This resulted in thyroid products with varying quality. The FDA has issued stronger requirements that have largely corrected this problem.

Generics versus Brand-Name Products. Generic brands are available and are subject to the same FDA guidelines as brand-name products. There is still debate over whether generic thyroid preparations are as effective as brand products.

Any change, such as being switched between brand-name and generic or between two different generics, requires additional testing of thyroid hormone levels. Many doctors still prefer to use brand-name products, noting that the cost difference between brand and generic thyroid drugs is not substantial. Regardless of which type is used, once a patient is stable, doctors generally recommend sticking with one type or brand since potency often varies from one drug to the next.

Natural Thyroid Hormone. Dried powdered thyroid hormone (such as Armour Thyroid, S-P-T, Thyrar, and Thyroid Strong) is made from animal glands. It was once the most common form of thyroid therapy, but it is no longer generally recommended because potency varies. Some people argue that with stricter FDA regulations, this natural form is better controlled and may even reduce the risk of developing autoimmunity factors. Dried thyroid also contains both T3 and T4 and is favored as a natural treatment by many alternative practitioners. However, studies need to be conducted to evaluate its benefits.

T3 and T4 Combinations. Triiodothyronine (T3), the other important thyroid hormone, is not ordinarily prescribed except under special circumstances. Most patients respond well to thyroxine (T4) alone, which is converted in the body into T3. In addition, the use of T3 may cause disturbances in heart rhythms. Some patients treated only with thyroxine continue to have mood and memory problems or other symptoms.

Combination products containing T4 and T3, such as liotrix (Thyrolar), are available, but there is some controversy concerning their benefits. Several recent studies have indicated that although some patients may prefer combination therapy, T3 and T4 together do not work better than T4 alone. Patients might like the combined drugs because they cause more weight loss, or a placebo effect may be involved. It does not appear that combination products offer any advantage for normalizing TSH levels.

Levothyroxine Regimens

Levothyroxine needs to be taken only once a day. It is slowly assimilated by body organs, so it usually takes up to 6 weeks before symptoms improve in adults. Nevertheless, many patients feel better after 2 - 3 weeks of treatment. The speed at which specific symptoms improve varies:

• Weight loss, less puffiness, and improved pulse usually occur early in the treatment.
• Improvements in anemia and skin, hair, and voice tone may take a few months.
• High LDL ("bad cholesterol") levels decline very gradually. HDL ("good cholesterol") levels are not affected by treatment.
• Goiter size declines very slowly, and some patients may need high-dose thyroid hormone (called suppressive thyroid therapy) for a short period.

Levothyroxine reduces blood pressure in about half of hypothyroid patients with hypertension, although blood pressure medications may still be needed.

Appropriate Dosage Levels. Initial dosage levels are determined on an individual basis and can vary widely, depending on a person's age, medication condition, other drugs they are taking, and, in women, whether or not they are pregnant. For example, pregnant women with hypothyroidism may need higher than normal doses.

• Starting out. Most people need to build up gradually until they reach a maintenance dose. In uncomplicated cases, the dose typically starts at 50 micrograms per day, which then increases in 3- to 4-week intervals until thyroid hormone levels are normal. Seniors and those with heart disease may start at 12.5 - 25 micrograms per day. On the other hand, young adults with a short history of hypothyroidism might be able to tolerate a full maintenance dosage right away.
• Maintenance dose. Maintenance dose for most patients averages 112 micrograms, but it can vary between 75 - 260 micrograms. If conditions such as pregnancy, surgery, or other drugs alter hormone levels, the patient's thyroid needs will have to be reassessed.

Daily Regimen. Because thyroid replacement is usually lifelong, setting up a regular daily routine is helpful. Here are some tips to remember:

• Establish a habit of taking the medication at the same time each day. This may help prevent missed doses.
• Levothyroxine is very forgiving. The hormone remains in the body for several days, so one missed dose should not cause a noticeable decline in well-being. The patient can safely take two doses the next day.
• Fiber and common daily supplements, such as calcium, may interfere with thyroxine absorption. Although levothyroxine can be taken at any time of day, either with or without food, some doctors recommend taking thyroid hormone upon awakening and at least 30 minutes before eating anything, including breakfast or supplements.

Annual Evaluation. Thyroid failure is an ongoing process and so is its treatment. Many factors can cause changes that require modifying the thyroxine dosages.

A dose that is appropriate for one year may be too low the next. To maintain normal thyroid levels, some patients may need to take gradually increasing doses of thyroid hormone every year or two. Doctors recommend that patients be reevaluated 6 months after normal TSH levels have been reached and then once a year thereafter.

Specific factors, such as changes in health or diet, new medications for other conditions, or simply switching brands, can also cause changes in thyroid hormone levels that require different doses. If patients change dose levels or thyroxine brands, they should be checked again at least 6 weeks later.

Problems Encountered with Levothyroxine Treatment

Because levothyroxine is identical to the thyroxine the body manufactures, side effects are rare. Over- or under-dosing, however, is fairly common, although rarely serious in the short term.

No Symptom Improvement When Normal Thyroid Levels Are Reached. Some patients fail to feel significantly better even when their thyroid levels become normal after taking thyroid replacement.

Some patients with persistent symptoms may benefit from triiodothyronine (T3), the other important thyroid hormone. In such cases, either a combination of a lower-dose of thyroxine with a small amount of T3 or natural dried thyroid hormone, which contains T3, may be helpful.

Side Effects of Overdosing. Overdosing can cause symptoms of hyperthyroidism. A patient with too much thyroid hormone in the blood is at an increased risk for abnormal heart rhythms, rapid heartbeat, heart failure, and possibly a heart attack if the patient has underlying heart disease. Excess thyroid hormone is particularly dangerous in newborns, and their drug levels must be carefully monitored to avoid brain damage.

Side Effects of Long-Term Treatment. Patients with hypothyroidism usually receive lifelong levothyroxine therapy. There has been some concern that long-term use will increase the risk of osteoporosis, as suppression therapy does. Studies indicate that postmenopausal women who are taking long-term replacement thyroxine at the appropriate dosage have no significantly increased risk for osteoporosis.

Drug Interactions with Levothyroxine. Many drugs interact with levothyroxine and may either enhance or interfere with its absorption. These drugs include:

• Amphetamines
• Anticoagulants (blood thinners)
• Tricyclic antidepressants
• Anti-anxiety drugs
• Arthritis medications
• Aspirin
• Beta blockers
• Insulin
• Oral contraceptives
• Digoxin
• Certain cancer drugs
• Iron replacement therapy (ferrous sulfate)
• Calcium carbonate and aluminum hydroxide
• Anticonvulsants (phenytoin, phenobarbital, carbamazepine)
• Rifampin (antibiotic used to treat or prevent tuberculosis)

Large amounts of dietary fiber may also reduce the drugâ ' s effectiveness. People whose diets are consistently high in fiber may need larger doses of the drug. Since thyroid hormones regulate the metabolism and can affect the actions of a number of medications, dosages may also need to be adjusted if a patient is being treated for other conditions. Even changing thyroxine brands can have a different effect.

Inappropriate Use of Thyroid Hormone

Thyroid replacement hormone is sometimes prescribed inappropriately. It should only be used to treat diagnosed low thyroid. In some cases of infertility, women with menstrual problems and repeated miscarriages and men with low sperm counts have been treated with thyroid hormones even when there was no evidence of thyroid abnormalities.

Other inappropriate uses for thyroid hormones are for weight loss and to reduce high cholesterol levels. Thyroid hormones have also been given to treat so-called metabolic insufficiency. Vague symptoms suggesting low metabolism, such as dry skin, fatigue, slight anemia, constipation, depression, and apathy, should not be treated indiscriminately with thyroid hormone. No evidence exists that thyroid therapy is beneficial unless the patient has proven hypothyroidism. Indiscriminate use of thyroid hormones can weaken muscles and, over the long term, even the heart. One exception is the use of thyroxine to enhance drugs used for the treatment of severe depression.