Thyroid Pharmacology Flashcards
What is the T4 thyroid hormone replacement rpeparation?
Levothyroxine
What is the T3 thyroid hormone replacement preparation?
Liothyronine
What are Thioamines used for?
for the treatment of hyperthyroidism
and to prepare for thyroid surgery
What are the 4 examples of thioamines?
methimazole
Carbimazole (which metabolizes to methiomazole)
Propylthiouracil
Potassium Iodide
What did Japanese citizens use to counter radioactive potential exposure to iodine after the Fukushima Daiichi nuclear disaster?
potassium iodide
How is levothyroxine typically dosed?
once daily
What is the half life for levothyroxine?
about 7 days
What are some things that will decrease the absorption of levothyrosine?
iron
calcium
alcohol
soy products
Should you lower or increase the dose of levothyroxine during pregnancy?
need to increase is by 30-50%
What are the adverse effects of iatrogenic hyperthyroidism (if you take too much)?
palpitations tremors anxiety weight loss tachycardia increased # of bowel movements arrhythmia/angina/MI in those with heart disease
atrial fibrillation in the elderly
bone loss with chronic oversupplementation
Which ones has greater potency - Levothyroxin or Liothyronine?
liothyronine (T3)
So when is liothyronin most useful?
when a quick onset is desirable
What is the half-life of liothyronine though?
only about 2 days - shroter than levothyroxine
What drug class inhibits thyroid hormone synthesis?
the thioamides
Again, what are the three major thioamindes?
methimazole
carbimazole
propylthiouracil
What enzyme do the thioamides inhibit?
thyroid peroxidase
Propylthiouracil also inhibits a second enzyme, which is?
Deiodinase 1
What is the duration of action for PTU? How about methimazole/
12 hours for PTU and 24 hours for methimazole
How long does it take for these thioamides to take effect?
2 weeks
Thioamides are the first line of attack in what disease?
Graves
What are the three main uses for iodine in the context of hyperthyroidism?
- preparation for thyroidectomy
- treat thyroid storm
- protection from radioactive iodin
Why do high concentrations of iodine help in hyperthyroidism?
because high concentrations inhibit almost all aspects of iodine metabolism, including thyrport, synthesis of iodotryrosines and iodytronines and release of thyroid hormones
True or false: “escape” from iodine treatment can occur.
true
What are the major side effects of iodine?
allergic reactions
sore teeth and gums
excess salivation
What are the two forms of radioactive iodine we use?
123-I
131-I
What is 123-I used for?
to scan the thyroid in nuclear imaging studies
What do we use 131-I for?
to destroy the thyroid in cases of hyperthyroidism not caused by Graves
131-I is painless, easy to administer, cheap and effective. But what’s the disadvantage?
often too much destructione
How do you need to manage a person after 131-I treatment/
need to supplement thyroid hormones
About how long do patients with GRaves disease need to be on antithyroid drugs?
usually a course of 12-18 months
but note: recurrence rates of ATD are high
What is the percentage of Graves patients that have a permanent remission after ATD discontinuation?
30-50% in adults
30% in children
What is the FDA warning on propylthiouracil?
there is risk of serious liver injury including liver failure and death
monitor closely during the first six months after initiating therapy and so opt for methimazole instead!
What is the rare side effect that has been reported with methimazole during pregnancy? So what does this mean in deciding what drug to give?
rare cases of emryopathies like aplasia cutis have been reported with methimazle during pregnancy, but no cases reported with propylthiouracil use
so PTU might be more appropriate for patients with Graves disease whoa re in their first trimester of pregnancy
