Thyroid Hormones & Conditions | Medicine Study Terms

Medications and conditions that can cause hypothyroidism

I TALC

S/sx hypothyroidism

Dx hypothyroidism

low T4, high TSH

S/sx hyperthyroidism

dx hyperthyroidism

Low TSH, high T4

Levothyroxine Tablet Colors

What is Synthroid?

levothyroxine (T4)

What is Levoxyl?

levothyroxine (T4)

What is Unithroid?

levothyroxine (T4)

What is Armour Thyroid?

Thyroid, Desiccated USP (T3 and T4)

What is Cytomel?

Liothyronine (T3)

Hypothyroidism Monitoring

TSH q4-8 weeks until normalized

Dose changes

• 4 weeks for larger dose changes

• 8 weeks for smaller dose changes

What is the levothyroxine starting dose?

1.6 mcg/kg/day using IBW

if CAD then 12.5 - 25 mcg daily

All levothyroxine brands and generics are the same. T/F?

F. check the therapeutic equivalence in the orange book

Levothyroxine: Counseling

- take with water at same time each day

- take at least 60 min before breakfast or at bedtime at least 3 hours after last meal

Levothyroxine IV:PO

0.75:1

When is IV levothyroxine used?

myxedema coma (life-threatening condition characterized by poor circulation)

Thyroid hormone replacement in elderly

too high replacement dose can cause Afib and fractures

Which thyroid hormone has a shorter half-life?

T3 (liothyronine)

What medications can decrease levothyroxine absorption?

- antacids

- polyvalent cations (Al, Mg, Fe, multivitamins)

- orlistat

- sevelamer

- sucralfate

separate by 4h

Medications and conditions that can cause hyperthyroidism

- Most common cause is Grave's disease

Meds:

- iodine

- amiodarone

- interferons

Hyperthyroidism Tx

- antithyroid meds (PTU/methimazole)

- radioactive iodine

- surgery

BBs can be added for sx control (tremors, palpitations, tachycardia)

1-3 months tx to control sx --> reduce dose at this time to reduce risk hypothyroidism

What is PTU?

propylthiouracil

thionamine

inhibits synthesis of thyroid hormones & conversion of T4 to T3

T4 vs T3

T4 has a long half life in blood, but is inactive. T3 has a short half life in blood and is very active (t3 has one less iodine)

T4 gets converted into T3

What is methimazole?

thionamine

inhibits synthesis of thyroid hormones & conversion of T4 to T3

PTU: BBW

Severe liver injury and acute liver failure

What antithyroid is preferred for pregnancy?

PTU for 1st trimester

Methimazole for 2nd & 3rd trimester

Which antithyroid is the drug of choice?

Methimazole for hyperthyroidism b/c lower risk liver damage

Which antithyroid is the drug of choice for thyroid storm?

PTU

PTU/Methimazole: Warnings and SEs

Warnings: hepatotoxicity

SEs: GI upset

S/sx thyroid storm

Thyroid storm Tx

- PTU

- inorganic iodide therapy with SSKI or Lugol's Solution

- BB (propranolol) + Systemic steroid (dexamethasone) + aggressive cooling (APAP & cooling blankets)

What is KI used for?

prevents thyroid cancer by blocking the accumulation of radioactive iodine in the thyroid gland