Thyroid Drugs

Therapeutic Overview

For hypothyroidism we administer exogenous T3 or T4 hormone (Synthroid), because there is not enough hormone present.

For hyperthyroidism (less frequently encountered) there is an overactive thyroid usually caused by a tumor. To correct it we can use surgery, radioactive iodine, drugs (Thioureylenes, beta-Adrenergic receptor blockers (used only to manage symptoms), corticosteroids (for anti-inflammatory effects, manage overactive thyroid, important in treating Graves Disease), and Iodides).

Hypothyroidism

• Primary failure of thyroid goiter
• Secondary to hypothalamic or anterior pituitary failure no goiter
• Lack of dietary iodine goiter

Hyperthyroidism

• Abnormal presence of thyroid-

• Secondary to excess hypothalamic or anterior pituitary secretion goiter
• Hypersecreting thyroid tumor no goiter

The most important anti-thyroid compound is propylthiouracil. This is the most common drug seen in the pt who has been diagnosed with hyperthyroidism. Propylthiouracil affects the processing of T4 in peripheral tissues. Although the thyroid gland secretes some T3, about 80% of the T3 in humans originates from 5’-deiodination of T4 in extrathyroidal tissues.

The half-life of thyroxine (T4) is relatively long (5 days), while Propylthiouracil and Triiodothyronine (T3) have relatively short half-lives (2 days). Sometimes propylthiouracil takes weeks to act. All of these drugs are orally effective.

Corticosteroids are useful in the tx of hyperthyroidism, especially of Graves’ disease. They don’t act specifically on the thyroid itself, but peripherally they act to slow the conversion of T4 to T3, have an immunosuppressive effect on Thyroid-Stimulating antibodies, and are antipyretic. These steroids are used in pts with severe hyperthyroidism who become hypotensive. Remember that anyone taking steroids chronically probably has zero endogenous cortisol, so on the day of the dental appointment be sure to give them 2x their cortisol dose.

Treatment of hypothyroidism usually involves replacement of thyroid hormone adequate to meet the pt’s needs. Four types of preparation are available: levothyroxine (T4) (Synthroid); triiodothyronine (T3); liotrix (combo of T3 and T4); and desiccated thyroid or thyroid extract (use of this is decreasing). T4 is preferred and used almost universally.

Clinical Problems

Iodide (not used much anymore): angioedema, hemorrhage, sore teeth and gums, salivation, induction of goiter and myxedema.

Thioureylenes: agranulocytosis, granulocytopenia, skin rash

Thyroid Preparations (including Thyroxine): Drug interactions with warfarin, bound (T4, T3) by cholestyramine in GI tract.

Category: Pharmacology Notes