Pharmacology-Thyroid & Parathyroid Flashcards
Why is it important to test expecting mothers’ thyroid levels?
The fetus depends on mother’s thyroid hormone until 2nd trimester and will become mentally retarded if deficient. Since pregnancy adds extra burden to the thyroid, pregnancy may exacerbate subclinical hypothyroidism.
Why is hyperthyroidism particularly concerning for people with coronary heart disease?
T3/T4 sensitize beta-adrenergic receptors and make the heart beat harder.
Why are people with hypothyroidism at increased risk for atherosclerosis?
T3/T4 increase LDL receptors in the hepatocytes. If T3/T4 is deficient, more LDL will circulate in the blood.
Hypothalamic Pituitary Thyroid access
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What happens when TSH from thyrotrophs binds to follicular cells in the thyroid?
PKA turns on thyroid peroxidase and the Na/I symporter. Thyroid peroxidase makes iodine from iodide. Organification occurs as I is complexed to tyrosine on thyroglobulin to form MIT & DIT, which is stored in colloid. MIT and DIT combine to form T3 and T4 on thyroglobulin, which is then proteolyzed and T3/T4 are released and thyroglobulin is recycled.
How is T4 activated and how is it deactivated?
Activated and deactivated by deiodination. Activation forms T3, deactivation form rT3.
What drugs can deactivate thyroid hormone in peripheral tissues?
Amiodarone, beta-blockers and corticosteroids. These prevent the deiodination of T4 to form T3 and only allow for formation of rT3.
How does T3 activate genes?
Acetylation releases gene repressors and allows activator to bind and induce transcription of DNA.
Symptoms of myxedema/hypothyroidism?
Cold, eyelid edema, pallor, thin hair, lethargy, poor memory, bradycardia, weight gain, hypercholesterolemia, constipation, amenorrhea.
Drug of choice for hypothyroidism
Levothyroxine (T4)
Treatment of hypothyroidism prior to surgery or in myxedema coma?
IV sodium liothyronine (T3)
Drug that is given in the natural ratio (4:1) of T4:T3.
Liotrix
Why take T4 replacement of T3?
T4 has a longer half-life than T3
Symptoms of hyperthyroidism
Hot, sweaty, palpitations, nervous, weight loss, insomnia, diarrhea and exopthalmos
What activities are inhibited by thioamides? What are the thioamides?
Propylthiouracil (PTU), methimazole & carbimazole. They inhibit thyroid peroxidase and thus inhibit organification of iodine and T3/T4 synthesis.
Why only use PTU in the 1st trimester?
PTU does not cross the placenta as much as methimazole, lowering the risk of hypothyroidism in the child.
A patient comes to the ED complaining of palpitations, fever, flushing and sweating. ECG reveals atrial flutter tachycardia and labs show high levels of T3 and T4. How do you treat this patient?
She has thyroid storm, thyrotoxic crisis due to super sensitization of beta-adrenergic receptors. You treat with beta blockers (propranolol or atenolol) and can use Lugol’s solution (KI + I2) to diminish vasculature of the thyroid temporarily (Wolff-Chaikoff Effect)
Why are the parathyroids spared when you treat someone with I-131?
The beta particle of the radioactive iodine is destructive but does not travel very far.
How do you follow up treatment of I-131?
Life-long levothyroxine supplementation due to loss of thyroid tissue.
In the case of nuclear fallout, what can you give to prevent thyroid damage?
Prophylactic KI prevents uptake of radioactive iodine.
3 hormones that regulate serum Ca2+
PTH, 1,25-dihydroxycholecalciferol, calcitonin
How does PTH affect the kidney, intestine and bone?
Kidney: decreases Ca excretion and increases PO4 excretion, increases 1-hydroxylase activity. Intestine: 1,25(OH)2D3 made from 1-hydroxylase increases Ca uptake from gut. Bone: induces expression of RANKL and activates osteoclasts
Where does the 25 hydroxylation of vitamin D take place?
Liver
Usual treatment for hyperparathyroid adenomas
Surgery, you really only need one of you four parathyroids to survive
