Kinder, thyroid drugs Flashcards
What thyroid agents do we use
levothyroxine T4
liothyronine T3
what are the antithyroid agents
methimazole
propylthiouracil
potassium iodide
how is iodide transferred into thyroid gland
Na/iodide symporter
what anions impair iodide transport
thiocyanate, pertechnetate, perchlorate
how does iodide travel to the follicular lumen
iodide transporter called pendrin
what oxidizes iodide
thyroidal peroxidase
what do thioamide drugs block
thyroid peroxidase
what drugs can inhibit 5’ deiodinase needed to convert T4 to T3
amiodarone, iodinated contrast media, beta blockers, corticosteroids, severe illness, starvation
what inhibits TSH release
somatostatin, dopamine T3T4
thyroid effects are from what process
activation of nuclear R leading to protein synthesis
which type of thyroid syndrome causes decreased drug metabolism? increased warfarin requirement?
hypothyroidism
where is T4 absorbed
duodenum and ileum
what can alter absorption of given thyroid hormones
severe myxedema with ileus
how does T3 T4 clearance change in hypo and hyper thyroidism
in hyper clearance is increased
in hypo clearance is decreased
what agents increase hepatic CYP and enhance degradation of thyroid hormone
rifampin, phenobarbital, carbamazepine, phenytoin, HIV protease inhibitors
what agents interfere with T4 absorption
oral bisphosphonates, bile acid sequestrants, cipro, ppis, sucralfate, antacids, bran, soy, coffee
what agents induce autoimmune thyroid disease with hypo or hyperthyroidism
INF-a
lithium
amiodarone
CI T2 liothyronine
those with cardiac disease because increased risk for cardiotoxicity
why is T3 replacement not commonly used
requires multiple daily dosing, higher cost, difficulty monitoring
what are the thioamides
meth`imazole, propylthiouracil
MOA thioamides
prevent thyroid hormone synthesis
inhibit thyroid perozidase catalyzed reactions, blocks iodine organification, blocks coupling of iodotyrosines
what additional affect does PTU have
peripheral deiodination T4 to T3
onset of action of thioamides and why
slow 3-4 weeks before stores of T4 depleted because affects synthesis not release
What thioamide is more portent
methimazole
what thioamide is rec for pregnant women in 1st trimester or someone in thyroid storm
PTU
why is PTU preferred in pregnancy
protein bound so crosses placenta less readily
adverse effects to thioamides
maculopapular rash with fever sometimes
urticarial rash, vasculitis, lupus-like reaction, lymphadenopathy, hypoprothrombinemia, exfoliative dermatitis, acute arthralgia
What is an adverse effect PTU
severe hepatitis
most dangerous complication with thioamides
agranulocytosis
What are the anion inhibitors we use in hyperthyroidism
perchlorate, pertechnetate and thiocynate which competitively inhibit iodide transport mech blocking iodide uptake
what is MOA potassium iodide
inhibit iodide rganification and hormone release, decrease size and vascularity of hyperplastic gland
major action potassium iodidie
inhibits hormone release (possibly inhibition thyroglobulin proteolysis)
therapeutic use of potassium iodide
thyroid storm
preoperative reduction hyperplastic gland
block thyroidal uptake of radioactive isotopes of iodine in a radiation EM
after thioamide therapy
why do you use potassium iodide after thioamide use
may delay thioamide by increasing intraglandular stores of iodine
whye should iodides never be used alone
gland escapes block in 2-8 weeks and withdrawl may produce severe exacerbation of thyrotoxicosis in iodine enriched gland
Adverse effects iodidies
uncommon
acneiform rash, swollen salivary glands, mucous membrane ulcerations, conjunctivitis, rhinorrhea, drug fever, metallic taste, bleeding disorders, anaphylactic reactions
are iodides used in pregnancy
no because cross placenta and can cause fetal goiter
MOA radioactive iodine
destruction of thyroid parenchyma thorugh epithelial swelling, necrosis, follicular disruption, edema and leukocyte infiltration
advantages radioactive iodine
easy administration, effective, low expense, absence pain
CI RI iodine
pregnancy or breast feeding
destroys fetal thyroid gland
which medications can improve the Sx of hyperthyroism but do not alter the thyroid hormone
beta blockers: metoprolol, propanolol, atenolol
general Tx strategy for hashimoto
levothyroxine unless drug induced hypothyroidism
how long does it take for levothyroxine to work
6-8 weeks
signs of thyroxine toxicity
children: restless ness, insomnia, acclerated bone maturation and growth
adults: increased nervousness, heat intolerance, episodes of palpitations and tachy, unexplained weight loss
chronic overTx with T4 can lead to what
a fib and accelerated osteoporosis
hypothyroid patient has progressive weakness, stupor, hypothermia, hypoventilation, hypoglycemia, hypoNa and water intoxication, shocky
myxedema coma! medical EM!!
Tx myxedema coma
IV levothyroxine loading dose with following mainta=enance doses
What is your worry in myxedma with patient who has CAD
low levels thyroxine protect heart from increasing demands so want to avoid provoking cardiac event with drugs
what is preferred patient for antithyroid drugs
young patients with small glands and mild disease
preferred patient for thyroidectomy
large glands or multinodular goiters hyperthyroidism
what should you do prior to thyroidectomy
Tx with potassium iodide 10-14 days prior to diminish gland vascularity
preferred patient for radioactive iodine
over 21 y.o
no heart disease
how do you Tx patient with heart disease with Radioactive iodine
antithyroid drugs until euthyroid
stop medication 3-5 days before RAI, may resume 3-7 days post
taper antithyroid medication over 4-6 weeks as thyroid functio normalizes
what are adjunts to antithyroid therapy
beta blockers to control tachy, HTN and a fib
if patient cannot have beta blocker how do you treat heart when alost on antithyroid meds
diltiazem
CaCh blocker
management thyroid storm
beta blocker
potassium iodidie to prevent release of thyroid hormones
PTU to block synthesis
hydrocortisone IV to protect against shock
supportive therapy for fever, or underlying diseases
what is used last resort to lower circulating thyroxine in thyroid storm
oral bile acid sequestrants, plasmapheresis or peritoneal dialysis
