Thyroid Pharmacology

Question 1

A 25-year-old woman has been diagnosed as hypothyroid. What is the most appropriate single agent
 therapy to be prescribed to her?
A. Propranolol
B. Propylthiouracil
C. Liothyronine 
D. Thyrotropin
E. Levothyroxine

Answer 1

E
Levothyroxine is the primary drug used for thyroid hormone replacement therapy. While Liothyronine may sometimes be indicated as a second drug, it is rarely indicated for single use.

Question 2

Which of the following hormones/drugs primarily activates intracellular thyroid hormone receptors to regulate gene transcription in target cells?
 A. Thyrotropin
 B. TSH
 C. Levothyroxine
 D. Triiodothyronine
 E. Sermorelin
 F. Thyroxine

Answer 2

D
While thyroxine (T4) is the most abundant circulating form of thyroid hormone, the most potent activator of the thyroid hormone receptor is triiodothyronine. Thyroxine is delivered to target cells via the circulation. In target tissues, it is converted to T3 (triiodothyronine), which is the most potent activator of the thyroid hormone receptor. Liothyronine is the generic drug name for T3.

Question 3

A 35-year-old woman discusses with her endocrinologist that she would like to have a baby. She has been taking levothyroxine for 5 years for treatment of hypothyroidism, and she is concerned about what effect this might have on her pregnancy. The physician tells her to continue her current levothyroxine dose and be sure her obstetrician knows about her hypothyroidism and therapy. Which of the following might be expected in this woman when she becomes pregnant?
A) An increase in TSH levels indicating a need to increase the T4 dose
B) An increase in TSH levels indicating a need to decrease the T4 dose
C) A decrease in TSH levels indicating a need to increase the T4 dose
D) A decrease in TSH levels indicating a need to decrease the T4 dose

Answer 3

A
Pregnant women on thyroid replacement therapy usually need an increase in the dose while they are pregnant. This is thought to be due to increased circulating levels of TBG (thyroid binding globulin). The adequacy of the thyroxine dose is monitored by measuring TSH during pregnancy, just as at other times. If the T4 dose is not adequate as pregnancy proceeds, TSH will go up, signaling the need to increase the dose.

Question 4

Which of the following pharmacotherapies for hyperthyroidism results in decreased thyroid hormone secretion within a short time (day or less)?
A) Propylthiouracil
B) Propranolol
C) Potassium iodide

Answer 4

C
High extracellular iodide levels suppress thyroid hormone release directly and immediately (once sufficient iodide levels are achieved). Effective change in thyroxine levels resulting from propylthiouracil requires a much longer period of time, because it has little or no effect on release of preformed thyroid hormone. Propranolol does not affect secretion of thyroid hormones.

Question 5

A 52-year-old man complaining of a “racing heart,” weight loss, and heat intolerance is diagnosed with hyperthyroidism. Which of the following drug therapies would be most appropriate to rapidly treat his symptoms while further diagnostic tests are done and treatment decisions are made?
A) Propylthiouracil 
B) Liothyronine
C) Prednisone
D) Propranolol
E) Thyrotropin

Answer 5

D
Propranolol, a beta adrenoceptor antagonist can affectively help control the cardiac symptoms of hyperthyroidism without directly altering the thyroid status. Propranolol thus does not actually treat the hyperthyroidism itself, but it does help prevent some of the unpleasant and possibly dangerous effects, such as tachycardia.

Question 6

Propylthiouracil is an effective therapy for hyperthyroidism. Which of the following steps in thyroid hormone synthesis and/or release are directly regulated by this drug?
A) Iodide uptake into follicular cells
B) Deiodination of diiodotyrosine and monoiodotyrosine in follicular cells
C) Coupling of diiodotyrosyl residues (or di- and monoiodotyrosyl residues) to form thyroxine (or triiodothyronine)
D) Colloid proteolysis
E) Release of thyroid hormones from the thyroid gland

Answer 6

C
Thioamide drugs, including propylthiouracil inhibit thyroid peroxidase which is important for two keys steps in thyroid hormone synthesis: the oxidation of iodide to its active form, and the coupling of iodotyrosines. Both of these reactions occur in the extracellular colloid space surround by follicular cells.

Question 7

A 72-year-old woman is brought to the emergency department in a semi-lucid state. Her caretaker reports that the woman had felt unwell for several days and had quit taking her thyroid medication. Lab tests revealed severe hypothyroidism. Which of the following drug combinations is most likely to benefit this woman?
A) levothyroxine plus propranolol
B) levothyroxine plus liothyronine
C) liothyronine plus propranolol
D) levothyroxine plus propylthiouracil 
E) liothyronine plus propylthiouracil

Answer 7

B
Both liothyronine and levothyroxine should be administered to patients with severe hypothyroidism (myxedema crisis) because the patient’s illness may suppress the ability of target tissues to produce adequate liothyronine from levothyroxine alone. In addition, liothyronine can initiate more rapid responses than waiting for levothyroxine to be converted. The other drugs mentioned in the answer choices are all drugs that would be used to treat hyperthyroidism.