Thyroid Flashcards
Thyroid gland produces which two hormones?
Which hormone is more potent?
Which hormone has the shorter half life?
Which hormone is primarily formed by the breakdown of the other?
Which hormone is considered the active form?
T3 and T4 T3 is more potent T3 has the shorter half life T3 made from T4 Free T4 is considered the active form.
Explain the release of thyroid hormones and the negative feedback loop.
The hypothalamus releases TRH which tells pituitary to release TSH which tells thyroid gland to make T4 and to a lesser extent T3. This also converts T4 –>T3 in the periphery.
Feedback mechanism: Elevations in T4 and T3 will inhibit secretion of TSH and creates a negative feedback loop.
Explain what happens to the thyroid hormones in both hypo and hyperthyroidism?
Hypothyroidism: Low T4, High TSH
Hyperthyroidism: High T4, Low TSH
What are the main signs and symptoms of hypothyroidism and what autoimmune condition is responsible for the most cases of hypothyroidism?
Cold intolerance, dry skin, weight gain, constipation, muscle cramps, voice changes, muscle pain, weakness, depression, bradycardia, coarseness of loss of hair.
Hashimotos disease where patients antibodies attack their own thyroid gland.
What are the main signs and symptoms of hyperT and what autoimmune condition is responsible for the most cases?
Heat intolerance, weight loss (or gain), insomnia, tremor, thin hair, goiter, diarrhea, fatigue, agitation, tachycardia, palpitations
Graves disease:
Which drugs can cause hypothyroidism?
Amiodarone, CBZ, eslicarbazepine, interferons, lithium, OXC, PHT, tyrosine kinase inhibitors (sunitinib)
How frequently should TSH be monitored in hypothyroidism?
Q 4-6 weeks until normal, then 4-6 months, then yearly
What is the generic and 2 brand names for synthetic T3.
Liothyronine (Cytomel and Triostat)
Desiccated thyroid brand name and hormones contained?
T3 and T4. Armour Thyroid
Levothyroxine should be taken in the AM at least 1 hour before breakfast or bedtime at least how many hours after last meal?
3 hours after last meal if taken at bedtime
Starting dose for levothyroxine? What weight do we use?
What is the starting dose if the patient has known CAD?
- 6 mcg/kg/day (IBW)
12. 5-25 mcg/day
What main condition would warrant a decreased dose of levothyroxine?
Cardiovascular disease
What is the IV:PO dose conversion for levothyroxine?
0.75:1
What drugs can decrease levothyroxine absorption?
How far apart should you space these drugs?
Aluminum antacids, calcium, cholestyramine, iron, Mg, multivitamins, sevelamer, sucralfate, kayexelate, lanthanum
Space out by 4 hours.
3 main options to treat hyperthyroidism?
Surgery, radioactive iodine, anti-thyroid medications
What is the first line option for treating symptoms of hyperthyroidism?
Beta blocker to help with palpitations, tremors, tachycardia
When initiated at high doses, How many months does it take to control symptoms with anti-thyroid medications?
It takes 1-3 months at higher doses to control symptoms, then the dose is usually reduced to prevent hypothyroidism
What are the 2 generics/brands of the thionamides, what are they used for?
Polythiouracil (PTU)
Methimazole (Tapazole)
Indicated for hyperthyroidism
BBW associated with PTU?
Severe liver injury and acute liver failure
Which agent used to treat hyperthyroidism is preferred in 1st trimester? Which agent is preferred for 2/3 trimesters? Why?
PTU first
Methimazole during 2/3 trimesters
Increased risk of liver toxicity for PTU and fetal abnormalities for methimazole.
Which are the 1 most common side effect with PTU and methimazole? What are 2 uncommon, rare, but serious side effects?
Common: GI upset
Serious: Hepatitis, agranulocytosis
Which agent is preferred in thyroid storm? PTU or methimazole? Why?
PTU because it blocks synthesis of thyroid hormone
What are the 2 generic iodides used in hyperthyroidism?
How do they work?
Potassium iodide and iodide solution (Lugols)
Saturated solution of potassium iodide (SSKI, Thyroshield)
They temporarily inhibit secretion of thyroid hormones, T4/T3 will be reduced for several weeks but effect will not be maintained
What are the 9 signs or symptoms of thyroid storm?
Fever > 103 Tachycardia Tachypnea Dehydration Profuse sweating Agitation Delirium Psychosis Coma
