Pharm Final: Thyroid Hormones Flashcards
What is the function of the thyroid gland?
take iodine from food and convert to thyroid hormones thyroxine (T4) and triiodothyronine (T3)
these hormones regulate metabolism for almost every tissue in the body
How much of each hormone does the thyroid gland produce?
80% T4, 20% T3
but T3 is four times as strong
What happens if the thyroid hormones are low?
pituitary gland sends out TSH to make more hormones
What is the most common form of hyperthyroidism?
Grave’s disease
What is Grave’s disease?
autoimmune disease characterized by antibodies against TSH receptors, causing excess thyroid hormone
What is most common form of hypothyroidism?
Hashimoto’s caused by destruction of thyroid gland
What is common feature of Hashimoto’s?
iodine deficiency/excess, however rare in the US
What drugs can cause hypothyroidism?
lithium carbonate and amiodarone
What are signs of hypertyroidism?
heat intolerance, nervousness, insomnia, fast heart rate, weight loss, muscle weakness
TSH is low, Free T4 is high
What is the goal of treatment for hyper?
treating sx with BB and using drugs that aim to decrease thyroid hormone synthesis
When should pts be started on BB?
as soon as they are diagnosed with hyper assuming no contraindications
What are the other three classes used to treat hyper?
thionamides = methimazole and propylthioracil
these are known as antithyroids as they block conversion of T4 to T3
Which drug is prefered first line of tx in hyper?
Methimazole’s due to longer duration of action
also can be taken once daily, more rapid efficacy and lower incidence of AE
Why is PTU used?
more in pregnancy as it will not cross placenta as much
What is the time frame goal for thionamides?
attain euthyroid state within 3-8 weeks
this is followed by radio iodine or surgery or continuation of drugs for 1-2 years
What is radioactive iodine used for?
complete destrcution of thyroid tissue, administered orally
simple and relatively safe lasting 6- 18 weeks
What are general AE of thiomanides?
skin rash, itching may cause hypo
What are signs and sx of hypo?
weight gain, cold intolerance, muscle cramps, memory loss
TSH is high, free T4 is low
goiter due to lack of dietary iodine
What is drug goal for pts with hypo?
drugs that replace thyroid hormones that can contain either both T4 and T3 or just one or the other
What is the preferred drug in replacement therapy?
synthetic tyrosine or levthyroxine (T4)
80% is absorbed and the half life is 7 days with once daily dosing
Should levothyroxine be taken with food or on empty stomach?
empty stomach
What are typical AE with levothyroxine?
subclinical hyper if too much given most common sign is Afib most likely in older pts, can be more hypo if not enough is given,
Why else should elderly pts with CAD take be careful taking these?
thyroid hormone increasing myocardial oxygen demand which can be associated with arrhythmias, angina, MI
What are PT implications of these meds?
hypo- CO can be affected leading to low exercise tolerance
hyper- have overstimulated cardiovascular system may have tachycardia and HTN
