The majority of diagnosed hypothyroid patients are prescribed T4 replacement hormone medications. These are types/brands that replace low thyroxine levels, which is the T4 hormone that also converts into the other major thyroid hormone called T3 (triiodothyronine). Brands of thyroxine are also referred to as “levothyroxine sodium” and include Synthroid, Levoxyl, Levothroid and Unithroid.
Thyroxine-T4 Replacement Therapy and Impaired Conversion
Once a dose of T4-only replacement hormone is taken, the treated patient and treating doctor must depend on the T4 to successfully convert into T3 as it is needed in the body. In the majority of hypothyroid patients, this occurs adequately as needed; however, in a small percent of patients, they will experience “impaired conversion”. The lack of T3 being converted will keep them in a state of hypothyroidism or what might be referred to as “Low T3 Syndrome”. Monitoring for impaired conversion requires the treating doctor to retest the patient’s blood levels of both T4 and T3 to see if proper conversion is occurring.
Combination T4 and T3 Replacement Therapy
Some doctors, who treat hypothyroidism, prefer to prescribe combination T4 and T3 thyroid hormone replacement medications. They believe this type of therapy is superior to T4-only replacement whether impaired conversion is an issue or not. Brands of combination T4 and T3 thyroid hormone drugs, include Thyrolar and Armour Thyroid. Most cases of hypothyroidism are caused by “thyroid autoimmunity”, meaning there are auto-antibodies sent from the immune system, to attack thyroid proteins that convert iodine into thyroid hormones. Because of this, there can be a significant percent of hormone being blocked from conversion and this will cause the T3 level to remain at sub-optimal level, even when the dose of T4 coming into the body is adequate. While the T3 may remain within normal range, it will stay slightly below the mid-level of normal values or at lower normal.
The Treatment Goal for T4 and T3
Some hypothyroid patients may experience better symptom relief if both the T4 and T3 are at mid-range or higher-normal. This can be accomplished in most patients who are placed on a T4-only dose but for those whose ratio of T4 to T3 is not remaining balanced at mid-range or above, a combination of T4 and T3 thyroid hormone dose may offer the solution. This too is better determined by testing both thyroid hormone levels in treated hypothyroid patients. Testing the TSH alone (Thyroid Stimulating Hormone) may not detect a low T3 level either because this pituitary gland hormone may test at normal range even if the T4-only is at proper level.
Triiodothyronine-T3 Replacement Therapy
A dose of T3-only (Liothyronine Sodium) is usually restricted to cases of “Low T3 Syndrome” or what is also commonly referred to as “Euthyroid Sick Syndrome” or “Wilson’s Syndrome”. This condition of low T3 can occur in heart disease patients, in athletes who undergo strenuous training and in people with severe depression or chronic stress. It can also occur in cancer patients and in other cases of chronic or inflammatory diseases. A T3 dose of thyroid hormone replacement may be administered to patients with this type of hypothyroidism caused by low T3 levels. The cause of the hypothyroidism will also be treated or corrected and if significant improvement occurs, the T3 replacement therapy may only be needed temporarily (short-term). Medscape- Euthyroid Sick Syndrome
Doses of T3-only hormone medications are also sometimes added to T4 doses in hypothyroid patients so that the treating doctor can choose the ratio of T4 to T3 he deems necessary for the patient. The most recognized brand of T3 hormone available is called “Cytomel”, manufactured by King Pharmaceuticals. Some doctors may also refer their hypothyroid patients to compounding pharmacies who combine the needed ratio of T4 to T3 into a specially manufactured dose, tailored to the individual patient’s needs.
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