thyroid pharm Flashcards
Thyroid agents
levothyroxine (T4)
liothyronine (T3)
antithyroid agents
methimazole
PTU
potassium iodine
radioactive iodine
what will block the Na/I cotransporter?
thiocyanate (SCN)
pertechnetate
perchlorate
high intrathyroidal iodine can block what?
thyroidal peroxidase
what can inhibit 5’deiodinase
amiodarone iodinated contrast media beta-blockers corticosteroids severe illness starvation PTU
MOA of thyroid hormones
- T4 -> T3 via cytoplasmic 5-deiodinase
- T3 into nucleus
- TR bound to DNA TRE
- T3 binds TR and displaces corepressor
- activated TR binds RXR -> transcription
T4 absorption
in duodenum and ileum
must be given 1 hr before meals or 4 hours after meals and other drugs
which thyroid drug more bioavailable?
liothyronine
severe myxedema with ileus
can decrease absorption of TH and should be given IV
metabolism of TH in hyperthyroidism
clearance is increased
half-life is decreased
metabolism of TH in hypothyroidism
clearance is decreased
half-life is increased
agents which increase hepatic metabolism of TH
rifampin phenobarbital carbamazepine phenytoin HIV protease inhibitors
agents which interfere with T4 absorption
PO biophosphates bile acid sequestrants cipro proton pump inhibitors sucralfate anacids bran soy coffee
agents which induce autoimmune thyroid disease
interferon
lithium
amiodarone
what is the TH drug of choice
levothyroxine
why is liothyronine not the drug of choice
it is more potent, but has shorter half life and must be dosed more often
more expensive
difficult to monitor
has greater cardiotoxicity effects
desiccated TH
never should be used
thioamides MOA
prevent TH synthesis: block peroxidase block organification blocks coupling of MIT and DIT to TG PTU also inhibits T4 -> T3 onset of action is 3-4wks
methimazole
drug of choice
10x more potent then PTU
completely absorbed
safe for breast feeding
PTU
used in pregnancy and thyroid storm
thioamides common ADRs
most common is maculopapular rash
fever
GI and nausea
thioamides rare ADRs
urticarial rash vasculitis lupus-like rxn lymphadenopathy hypoprothrombinemai exfoliative dermatitis acute arthralgias cholestatic jaundice
block box warning of PTU
severe hepatitis
most dangerous complication of thioamides
agranulocytosis (<500)
must discontinue
cannot switch they x-react
potassium iodide MOA
inhibit iodine organification and hormone release
decrease size and vasulcarity of gland
*inhibits hormone release
uses of potassium iodine
thyroid storm
preoperative reduction of hyperplastic gland
block thyroidal uptkae of radioactive isotopes in radiation emergency
never can be used alone b/c effects wear off in 2-8 weeks and will become have rebound
avoid if near future radiation Tx will be used
ADRs of potassium iodine
uncommon rash swollen salivary glands mucous membrane ulcerations conjuctivitis rhinorrhea drug fever metallic taste bleeding anaphylaxis
CI of potassium iodine
pregnancy
CI of radioactive iodine
pregnancy or breast feeding
adrenoreceptor-blockers
metroprolol
propanolol
atenolol
how long does it take for levothyroxine to reach steady state
6-8wks
myxedema common
end stage of untreated hypothyroidism
medical emergency
ICU with intubation and mechanical ventilation
loading IV levothyroxine
hydorcortisone IV
if they have coronary aa disease must correct very cautiously
what is the preferred patient population for antithyroidal drugs
young patients with small glands and mild disease
thyroidectomy preferred patient population
large glands or multi-nodular goiters
must obtain euthyroid via pharm before sugery
RAI preferred patient population
almost everyone 21+
heart disease
adjunct to antithyroid therapy
beta-blockers
diltiazem
thyroid storm
beta blocker potassium iodine PTU hydorcortisone supportive therapy if really bad can give oral bile sequestrants, plasmapheresis, or peritoneal dialysis
