Thyroid Flashcards
Functions of the thyroid
- produces hormones
- regulates metabolism
body temperature
cardiac and nervous systems
skin dryness
menstrual cycles
cholesterol levels
it is the only gland that absorbs iodine
Describe the pathophysiology of the thyroid hormones from hypothalamus to periphery
Hypothalamus -> Thyroid releasing hormone (TRH) –> pituitary (TSH- aka thyrotropin regulates growth and development)–> Thyroid–> T4 (thyroxine) and T3 (triiodothyronine, 3 iodines) to the periphery - most of the T4 gets converted to T3, only small amount of T3 is made by thyroid
there is a negative feedback loop to regulate this
hypothyroidism vs hyperthyroidism
decreased free T4, increase TSH - hypothyroidism
increased free T4, decreased TSH - hyperthyroidism
Hypothyroidism symptoms and causes and emergency
- slowed down everything
hard ones to remember:
depression
voice changes
menorrhagia
dry skin
feeling cold / cold intolerance
muscle cramps, myalgias
weakness
bradycardia
coarse hair/loss of hair
memory loss/impairment
weight gain
Goiter (lump felt on throat due to enlarged thyroid)
causes: hashimotos disease (autoimmune - antibodies attack), drugs, iodine deficiency
emergency : myxedema coma - full slowing of all their systems, life threatening - tx with IV levothyroxine
Drugs that cause hypothyroidism
I TALC
Interferons** (can also cause hyperthyroidism)
Tyrosine kinase inhibitors
Amiodarone ** (can also cause hyperthyroidism)
Lithium
Carbamezapine
Conditions: hashimotos disease ; others include anything that affects iodine, pituitary, or thyroid gland
Other drugs:
- oxcarbazepine
- eslicarbazepine
-phenytoin
when should we screen patients for hypothyroidism
60
normal T4 and TSH levels
0.9-2.3ng/dl = T4
0.3-3 mIU/L = TSH
how often should we monitor TSH and symptoms
every 4-6 weeks until levels are normal. as patients get older a reduction in their thyroid dose may be required.
once euthyroid, we can check every 4-6 months
Why do we need to caution for too high thyroid replacement dose in elderly
can cause afib and fractures
excessive doses of thyroid in any age patient can cause hyperthyroidism
what is FT4
it is part of the thyroid function test (TSH, T4, and FT4 (free T4)) and its monitored when tx hypothyroidism in pregnancy
true or false. while patient is on thyroid treatment in the U.S. they should also receive iodine supplementation
false. In the U.S. we supplement table salt with iodine, so goiter has been virtually eliminated.
If people are on a salt restricted diet they can supplement with iodine or eat iodine rich foods like meat, seafood, dairy, and some breads
Counseling points with levothyroxine
take the dose consistently!
it binds to everything, so take 60 min before breakfast with water OR take at bed time at least 3 hrs after the last meal and no snacks can be eaten after.
(avoid Ca2+, antacids, multivitamins, etc. – also avoid hepatic inducers bc they decrease the levels (amiodarone, beta blockers, protein bound drugs)
true or false: we can switch patients on different levothyroxine formulations because they are very interchangable.
false. avoid this. there are therapeutic equivalence issues with variable amounts and we don’t want to mess with the patients thyroid. If we need to interchange with levothyroxine, we can use the orange book.
Cytomel (liothyronine, T3), and desiccated thyroid (ex: Armour thyroid) aren’t recommended because they have variable amounts of T3 and T4.
Levothyroxine IV:PO conversion
0.75 IV: PO 1
75 % of oral dose
List the levothyroxine colors and strengths
Orangutans - orange = 25 mcg
Will - white = 50 mcg
Vomit - violet = 75 mcg
On - olive = 88 mcg
You - yellow = 100 mcg
Right - rose = 112 mcg
Before - brown = 125 mcg
They - turquoise = 137 mcg
Become - blue = 150 mcg
Large - lilac = 175 mcg
Proud - pink = 200 mcg
Giants - green = 300 mcg
these are standardized. great for safety checks so that the patient recognizes when they have wrong dose
Hyperthyroidism symptoms and causes
everything is sped up/heated up
heat intolerance/sweating
agitation
palpitations
tachycardia
light/absent menstrual periods
diarrhea
weight loss
tremor
thinning hair
exophthalamos - bulging eyes
cause: graves disease (autimmune- antibodies stimulate thyroid to increase T4), thyroid nodule, certain drugs (amiodarone, iodine, thyroid replacement drugs, interferons), excess hormone replacement.
Levothyroxine (T4) brand names
synthroid, levoxyl, unithroid, euthrix, tirosint, tirosint-SOL
available as capsule, tablet, and injection, and oral solution
separate this from other ion/chelating drugs by at least two hours (the longer the better)
full replacement dose for levothyroxine and who should get it. who should get partial replacement
full: 1.6 mcg/kg/day using IBW
healthy, young (<50 yrs) pts with high TSH
partial : elderly, or milder hypothyroidism and those with comorbidities. Elderly pts may need < 1mcg /kg/day, or 20-25% less per kg
What dose of levothyroxine should pts get if they have CAD
12.5-25 mcg daily
Desiccated thyroid (T3 & T4)
Armour thyroid tablets
15-30 mg daily and titrate up. usual dose is 60-120 mg /day
not recommended usually
Liothyronine (T3)
Cytomel tablet
Triostat injection
25 mcg daily , titrate. usually dosed 25-75 mcg daily
this drug has a shorter half life, which causes more fluctuations in T3 levels.
boxed warning for thyroid replacement hormone
never use for weight loss. high doses can cause fatal effects.
Contraindication for thyroid replacement hormone
uncorrected adrenal insufficiency
in what condition do we need to decrease the dose of thyroid hormone replacement therapy
patients with CVD (hypothyroidism increases risk of coronary artery disease)
T or F: thyroid hormone replacement therapy can cause osteoporosis
true. decreases BMD
SE of thyroid hormone replacement therapy
hyperthyroid symptoms if you give too much
(palpitations, tachycardia, arrythmias, irritability, sweating, weight loss)
levothyroxine doses likely need to be increased or decreased during pregnancy or breastfeeding ?
increased
thyroid hormone is highly protein bound so we need to be aware of other drugs that might compete with the protein and affect drug levels
ex: phenytoin
Thyroid hormones can impact the concentration/effect of warfarin and theophylline how?
increases warfarin effectiveness, increases INR
decreases theophylline
drugs that can cause both hypo and hyperthyroidism
amiodarone
interferons
Describe treatments for hyperthyroidism
radioactive iodine (RAI-131) or surgery - preferred in graves disease
Thionamides:
Propylthiouracil (PTU)- 50 - 150 mg Q8H until euthiroid, and eventually reduce - preferred in thyroid storm or in first trimester of preg.
OR Methimazole (topazole)** preferred in all pts d/t low risk of liver damage and in 2nd and 3rd trimester of pregnancy after PTU in first. mild hyperthyroidism: 5 mg Q8H, titrate to 5-15 mg daily
^both of these inhibit synthesis of thyroid hormones and conversion of T4 to T3. always monitor for liver tox. SE: GI upset, rash ,fever, constipation, bleeds
BOXED WARNING for severe liver injury and acute renal failure for both thionamides . both are teratogenic, but PTU is more, so preferred in first trimester.
Potassium Iodide (lugols solution) - temporarily inhibits secretion of T3 and T4 for several weeks but eventually diminishes. diluted and taken with water
Contraindicated if hypersensitive to iondide or iodidne or. has heart disease. SE: rash, sore throat/gum, GI upset. hyperthyroidism with prolonged use. off label for preparation for thyroidectomy or for after the radioactive iodine to prevent thyroid cancer
Beta blockers are used to help with symptoms (arrhythmia, tremors, palpitations, etc) Ex: propranolol
thyroid storm definition and symptoms and treatment
life threatening emergency, hyperthyroidism that caused by trauma, infection, surgery, radioactive iodine treatment or non adherence to antithyroid meds.
Sx: heightened version of hyperthyroidism, coma, psychosis, delirium
treatment:
PTU (propylthiouracil) AND potassium iodide solution, beta blocker (propranolol) systemic steroid (dexamethasone), aggressive cooling with APAP and other supportive tx.
true or false: levothyroxine can’t be used in pregnancy
false. it can. 30-50 % increase in the dose throughout the course of their pregnancy and several months after giving birth. we should aggressively control the hypothyroidism in pregnancy and ideally start treatment before pregnancy.
For hyperthyroidism, also should try and postpone pregnancy and treat hyper before. because there are risks to baby and mom. if hyper and becomes pregnant, see if tx can be stopped safely in mild disease otherwise (PTU first trimester, and methimazole 2nd and third
