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Chapter 27: Thyroid and Antithyroid Drugs

INTRODUCTION

This chapter will be most useful after having a basic understanding of the material in Chapter 39, Thyroid and Antithyroid Drugs in Goodman & Gilman’s The Pharmacological Basis of Therapeutics, 12th Edition. In addition to the material presented here, the 12th Edition contains:

  • A discussion of the chemistry and biosynthesis of the thyroid hormones.

  • Figure 39-1 Thyronine, thyroid hormones, and precursors, shows the chemical structures of the thyroid hormones

  • A detailed discussion of thyroid hormone metabolism and the conversion of thyroxine to triiodothyronine in peripheral tissues

  • A discussion of the actions of thyroid hormone including the non-genomic effects of thyroid hormones, the effects of thyroid hormone metabolites, the effects of thyroid hormones on growth and development, and the thermogenic, cardiovascular, and metabolic effects of thyroid hormones

  • Table 39-5 Selected Pharmacokinetic Features of Anti-Thyroid Drugs, shows selected pharmacokinetic features of propylthiouracil and methimazole

LEARNING OBJECTIVES

  • Understand the principles of thyroid hormone regulation.

  • Describe the diagnosis and treatment of hypothyroidism and hyperthyroidism, including during pregnancy.

  • Describe the treatment options for well-differentiated thyroid cancer.

DRUGS INCLUDED IN THIS CHAPTER

  • Carbimazole (NEO-MERCAZOLE)

  • Desiccated thyroid (ARMOR THYROID, others)

  • Iodide

  • Levothyroxine (l-T4, LEVOTHROID, LEVOXYL, SYNTHROID, UNITHROID, others)

  • Liotrix (a thyroxine/triiodothyronine 4:1 mixture; THYROLAR)

  • Methimazole (TAPAZOLE, others)

  • Propylthiouracil

  • Sodium iodine (IODOPEN)

  • Sodium iodine 131I (HICON, others)

  • Triiodothyroxine (CYTOMEL, TRIOSTAT, others)

MECHANISMS OF ACTION of THYROID AND ANTITHYROID DRUGS
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MECHANISMS OF ACTION of THYROID AND ANTITHYROID DRUGS
DRUG CLASS DRUG MECHANISM OF ACTION
Thyroid Hormone

Levothyroxine

Triiodothyroxine

Liotrix

Desiccated thyroid

 Binding of 3,5,3’-triiodothyronine T3 to thyroid hormone receptors (members of the nuclear receptor superfamily of transcription factors) on target tissues
Antithyroid Drugs

Propylthiouracil

Methimazole

Carbimazole

 Interferes with the incorporation of iodine into tyrosyl residues to form iodothyronine (see Figure 27-1)
Ionic Thyroid Inhibitors

Iodide

Sodium iodine

 At high concentrations, iodide inhibits the synthesis of iodotyrosines and iodothyronines; high concentrations also inhibit the release of thyroid hormones
Radioactive Iodine Sodium iodine 131I Incorporated into iodoamines and deposited into the colloid of thyroid follicles where the destructive β particles are released
THYROID FUNCTION TESTS
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THYROID FUNCTION TESTS
TSH (Thyroid-stimulating hormone) Elevated in hypothyroidism; decreased in hyperthyroidism
T4 (Thyroxine) Elevated levels suggest hyperthyroidism; decreased levels suggest hypothyroidism
T3 (Triiodothyronine) Elevated levels suggest hyperthyroidism; decreased levels suggest hypothyroidism
SYMPTOMS OF THYROID DISEASE
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SYMPTOMS OF THYROID DISEASE
HYPOFUNCTION HYPERFUNCTION
Fatigue Exophthalmus—Graves disease
Lethargy Excessive production of heat
Cold intolerance Increased motor activity
Mental slowness Increased sensitivity to catecholamines
Depression Flushed skin
Dry skin Warm moist skin
Constipation Weak muscles
Mild weight gain Tremulousness
Fluid retention Rapid, forced heart rate
Muscle aches Increased appetite
Irregular menses Weight loss if intake is inadequate
Infertility Heat ...

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