Thyroid Flashcards
Free T4
active form as most is bound to protein
What is myxedema coma?
when hypothyroidism decompensates’ life threatening emergency IV thyroid hormone should be administered
How often should free T4 and TSH be checked in hypothyroidism
every 6 to 8 weeks until normalized then 6 months later then yearly
what drugs are associated with causing hypothyroidism?
amiodarone interferons llithium nitroprusside TKIs (sunitinib)
levothyroxine is a pregnancy ___
A; increases of 30 to 50% may be necessary during pregnancy
when should thryoid hormone replacement be taken?
first thing in the morning; empty stomach at least 30 mins before breakfast
What can be taken after exposure to radiation to prevent an accumulation of radioactive iodine?
potassium iodide
liothyronine
T3
dessicated thyroid
T3 and T4 Armour Thyroid; dosed in grains
How is levothyroxine dosed initially?
in patients > 50 or in patients <50 with underlying cardiac diseasestart at 50mcg/d
in patients >50 with cardiac disease what is the start dose of levothyroxine
start at 12.5mcg/ day; titrate every 4 to 8w to 25mcg
what is the usual replacement dose of levothyroxine approxiamately?
0.5mcg/kg/d for elderly; 1.7 mcg/kg/d <50
What SEs are common with thyroid replacement?
should be none; counsel patients on sx of hyperthyroidism (increased HR tachycardia weight loss irritability)
What is the IV:PO ratio for levothyroxine?
1:2
What should be seperated from levothyroxine by 4 hours?
aluminum calcium cholestyrimine iron mg multivitamines (ADEK) folate orlistat sevelamer sodium ALL decrease absorption of levopolystyrine sucralfate
How long before levothyroxine starts working?
may see reduction in sx in 1to 2 weeks but not the full effect for 1 to 2 months (similar to antidepressants!)
What drugs can cause hyperthyroidism?
iodine amiodarone interferons
What are the two thionamides and what is their MOA?
propylthiouracil and methimazole; inhibit synthesis by blocking oxidation of iodine and PTU also inhibits peripheral conversion
What is a BB with PTU?
severe liver injury and acute liver failure
What are common SEs with PTU and methimazole?
GI upset HA rash itching fever hepatitis agranulocytosis
In pregnancy which thionamides are preferred and when?
PTU in the 1st trimester and methimazole in the 2nd and 3rd
What are the iodides products used to treat hyperthyroidism?
potassium iodide and iodide solution (Lugol’s) saturated solution of of potassium iodide (SSKI)
What is thyroid storm and how is it treated?
decompisated hyperthyroidism; 5 things PTU given 1 hr before iodide PLUS SSKI or Lugols PLUS beta blockade (ex. propranolol); PLUS corticosteroid PLUS aggressive cooling WITH APAP and cooling blankets
what are the contraindications for levothyroxine
Acute MI, thyrotoxicosis, uncontrolled adrenal insufficency
What is the starting dose of desicated thyroid is an elderly pt w/ cardiac issues
15mg
What agents decrease the absoprtion of levothyrosine
cholestyramine, Ca, Mg, Al, Fe, sucralfate, orlistat, chromium; levo should be taken 2hours before or 4 hours after these
What agents decrease thyroid levels
estrogens & CYP inducers
What agents reduce the conversion of T4 to T3?
BBs, amiodarone, steroids, PTU
