Drugs: Hypothyroid, Antithyroid, Calcium

Question 1

How does Levothyroxine work? What do we use it for?

What our some potential side effects?

Answer 1

T4 analog that binds to nuclear receptors. Leads to increased protein synthesis, increased metabolic rate, and increased B-receptors, which leads to an increased sensitivity to catecholamines.

We use it for hypothyroidism, so as you might expect, side effects typically include those of hyperthyroidism (tachycardia, heart failure, sweating, tremor, diarrhea)

Question 2

Levothyroxine targets T4. Is there a drug that targets T3?

Answer 2

Liothyronine targets T3 but it is not used routinely for hypothyroidism because it causes arhythmias and can precipitate heart failure.

Question 3

What two drug types do we use to treat hyperthyroidism? What are their general functions?

Answer 3

Thionamides and iodine

Thionamides inhibit thyroid hormone synthesis. Excess iodine reduces thyroid synthesis and release (via the Wolff-Chaikoff effect). Radioiodine ablates cells that make thyroid hormone.

Question 4

How do thionamides work specifically, and what are examples?

Answer 4

Methimazole and propylthiouracil (PTU)

Inhibit the enzyme thyroid peroxidase, which catalyzes the oxidation and organification of iodine in thyroid hormone synthesis. PTU, in addition, also inhibits peripheral conversion of T4 to T3

Question 5

When can we not use PTU and methimazole

Answer 5

PTU should be avoided as a first line agent due to the potential for severe liver failure. In pregnant patients, PTU is used during the first trimester only.

Methimazole is used during the second and third trimesters to reduce potential teratogenic effects.

Question 6

Side effects of thionamides

Answer 6

Rash urticaria, fever, nausea.

Major effects include agranulocytosis, thrombocytopenia, acute hepatic necrosis, vasculitis.

Question 7

Specific mechanism for iodine and examples of the specific medications given

Answer 7

We give Iodide and Radioiodine

Iodide is selectively concentrated in the thyroid gland for hormone synthesis. When given in large doses, it inhibits thyroid hormone release.

Radioiodine is also concentrated in the thyroid gland and emits beta and gamma radiation

Question 8

How do we use iodines and what side effects do we worry about?

Answer 8

Large doses of iodide are used in thyroid storm and before thyroidectomy to prevent thyroid storm.

Radioiodine is used for hyperthyroidism and adjunctive treatment for some thyroid cancers.

Side effects include metallic taste, excessive salivation, diarrhea, and rash.

Question 9

Discuss how Bisphosphonates work and what side effects we can expect. What drugs fall in this category?

Answer 9

Anything ending in -dronate.

These guys stabilize bony matrix, coat hydroxyapetite to prevent osteoclasts from resorbing bone. We use them to treat postmenopausal osteoporosis and in Paget’s disease to reduce bone turnover. Prevention of accelerated bone loss in patients on long-term high-dose glucocorticoid therapy.

Side effects include esophagitis, GI discomfort, and osteonecrosis of the jaw.

Question 10

What does calcitonin do and what side effects do we worry about?

Answer 10

Lowers serum calcium with mild analgesic properties for bone pain. We use it for states of high calcium (oh boy, hold on tight kids)

Side effects include runny nose, nasal discomfort, flushing

Question 11

What does Calcitriol do and what side effects do we worry about?

Answer 11

This is an activated form of Vitamin D that increases calcium absorption from the intestines. We use it for hypocalcemia, Vitamin D replacement in patients with end-stage renal disease.

Side effects include Vitamin D intoxication (hypercalcemia, polyuria, weakness, headache, somnolence, constipation)