Thyroid Agents

Question 1

Levothyroxine (Synthroid) MOA

Answer 1

• synthetic form of T4 - produces the same effects in the body as endogenous thyroid hormones - used to treat hypothyroidism

Question 2

Levothyroxine (Synthroid) ADRs

Answer 2

• CV: angina, BP increase, flushing, palpitations,
• CN: anxiety, headache, insomnia

Generally minimal side effects if adequate level maintained

Question 3

Levothyroxine contraindications

Answer 3

• caution in pts with CV disease (relative contraindications - start with a lower dose) - avoid after recent MI, thyrotoxicosis

Question 4

Levothyroxine pt education

Answer 4

• take in the morning, preferably before breakfast on an empty stomach to increase absorption
• do not take with any other medications/supplements

Question 5

Methimazole (Tapazole) MOA

Answer 5

• inhibits the synthesis of thyroid hormones (mostly T4) by blocking the oxidation of iodine in the thyroid gland - used to treat the side effects of hyperthyroidism

Question 6

Methimazole (Tapazole) ADRs

Answer 6

• urticaria (hives) - agranulocytosis

Question 7

Methimazole (Tapazole) Contraindications

Answer 7

• Not safe in the 1st trimester of pregnancy (ok for use in 2nd and 3rd trimester)

Question 8

Methimazole (Tapazole) patient education

Answer 8

• recommend that the patient not get pregnant while on these drugs
• 1-2 years of treatment typically required

Question 9

Propylthiouracil (PTU) MOA

Answer 9

• inhibits the synthesis of thyroid hormones by blocking the oxidation of iodine in the thyroid gland - blocks conversion of T4 to T3 in the peripheral tissues - used to treat the side effects of hyperthyroidism

Question 10

PTU ADRs

Answer 10

• urticaria - agranulocytosis - hepatitis (very hard on the liver)

Question 11

PTU Contraindications

Answer 11

• black box warning: hepatotoxicity - PTU is safe in the 1st trimester of pregnancy

Question 12

How does propylthiouracil differ from methimazole?

Answer 12

PTU also inhibits T4 to T3 conversion in peripheral tissues

Question 13

Drug of choice for pregnant women with graves disease in first trimester

Answer 13

Prophylthiouracil

Question 14

Hyperthyroidism: Radioactive Iodine treatment indications

Answer 14

older adults, cardiac patients, moderate-severe symptoms, and those that fail treatment with antithyroid drugs

Question 15

Explain the biofeedback mechanism of the HPO axis as it relates to thyroid hormones

Answer 15

The hypothalamus senses low circulating levels of thyroid hormone (Triiodothyronine (T3) and Thyroxine (T4)) and responds by releasing thyrotropin-releasing hormone (TRH). The TRH stimulates the anterior pituitary to produce thyroid-stimulating hormone (TSH). The TSH, in turn, stimulates the thyroid to produce thyroid hormone until levels in the blood return to normal. Thyroid hormone exerts negative feedback control over the hypothalamus as well as anterior pituitary, thus controlling the release of both TRH from hypothalamus and TSH from anterior pituitary gland

Question 16

Levothyroxine in pregnancy

Answer 16

• Levothyroxine is safe in pregnancy
• Increases in dose may be required