Thyroid meds Flashcards
What are the two thyroid hormones? What is the difference between the two?
T3 and T4
T3 have three iodines, T4 has four
What are the four general function of thyroid hormones?
growth
Development
Body temp
Energy metabolism
How are thyroid hormones taken up by thyroid follicles?
Na/I symporter
What causes the change from iodide to iodine?
Thyroid peroxidase
What do the thyroid follicles surround?
Follicle lumen (colloid)
What is organification of iodide?
Iodination of tyrosine residues within the thyroglobulin molecule
What are the amino acids that comprise thyroglobulin?
Tyrosine
What are the molecules that are combined to form thyroid hormones?
MIT and DITs
What is the ratio of T4:T3?
5:1
What does the thyroid follicle take up from the follicular space? How? What does this do?
Thyroglobulin
Phagocytosis
Degradation to T4
What molecule does T3/4 bind to in the blood?
Thyroxine binding globulin
Where is the T3 receptor found? What does it do there?
T3 receptor sits on the DNA on thyroid response element (TRE)
Represses gene expression
What happens to T4 when endocytosed into the cell?
Changed to T3 by 5’-deiodinase
Which form of thyroid hormone is the active one? Which is found in the highest amounts in the blood?
T3 is active form
T4 is highest in the blood
Describe the HPA axis in regards to the thyroid expression
TRH expressed by the hypothalamus, promotes TSH release by pituitary. This causes the release of thyroid hormone from the thyroid, which will feed back to the hypothalamus to inhibit further secretion
What is the effect of high iodide concentration?
Negative feedback on the thyroid
What is the effect of Low iodide concentration?
Promotes hormone synthesis
What are the two effects of the thyroid hormone on the sympathetic nervous system?
- Increase beta adrenergic receptors
2. Decrease alpha adrenergic receptors
What are the effects of the thyroid hormone on: growth and development?
- Brain development and neurogenesis
2. Bone growth and skeletal maturation
What are the effects of the thyroid hormone on: thermogenesis?
Increases cellular engery consumption
What are the effects of the thyroid hormone on: Respiratory?
Increase O2 consumption, causing increase RR
What are the effects of the thyroid hormone on: CNS?
- Rapidity of cerebration
2. Effect spinal cord synapses that control muscle tone
What are the effects of the thyroid hormone on: the GI tract?
Increase secretions and motility
What are the effects of the thyroid hormone on: skin and hair?
!. trophic effect
2. Prevent accumulation of glycosaminoglycans (causes water retention)
What are the effects of the thyroid hormone on: the CV system?
- Increase HR
- Increase contraction
- Increase CO
- Increased BP
- Decrease resistance
What are the effects of the thyroid hormone on: metabolism
Increase BMP
Increased protein synthesis
Decreased Fat level
Atherosclerosis is seen in hypo or hyperthyroidism
Hypo
Cold intolerance is seen in hypo or hyperthyroidism
Hypo
Low respiratory rate is seen in hypo or hyperthyroidism
Hypo
Diarrhea is seen in hypo or hyperthyroidism
Hyper
Dry and scaly skin, depressed hair and nail growth is seen in hypo or hyperthyroidism
Hypo
Fluid retention is seen in hypo or hyperthyroidism
Hypo
MR is seen in hypo or hyperthyroidism
Hypo
Vitamin deficiency is seen in hypo or hyperthyroidism
Hyper
Decrease in strength is seen in hypo or hyperthyroidism? Why?
Hyper, due to increased catabolism
What causes the increased fluid retention in hypothyroidism?
Accumulation of GAGs in interstitial space d/t decreased clearance
What is myxedema, and what is it seen in?
Swelling around the eyes in hypothyroidism d/t GAG accumulation
What is Cretinism?
Hypothyroidism d/tt lack of thyroid development of TSH receptor responsiveness
What is hashimoto’s thyroiditis? Is this hyper or hypothyroidism?
Infiltration of lymphocytes in the thyroid gland, causing destruction of the thyroid
Initially hyper when thyroid hormone stores released, then hypo when depleted
What medication cause destroy the thyroid?
Li
What are the causes of secondary hypothyroidism?
Head trauma Cranial neoplasm Brain infx Cranial irradiation Neurosurgery
What are the three synthetic thyroid hormones?
Levothyroxin
Liothyronine
Liotrix
What is levothyroxine?
Synthetic T4
What is Liothyronine?
Synthetic T3
What is Liotrix?
Synthetic mix of T3 and T4
Why is Levothyroxine given more often than Liothyronine?
Since T4 is more common in the blood, closer to physiologic concentrations
What is the complication of treating elderly pts with hypothyroidism and CAD?
Hypothyroidism is protective against CV problems, so “curing” hypothyroidism may cause increased in CV problems
What is the MOA of synthetic thyroid hormones?
Activation of T3 receptors,
What are the side effects of synthetic thyroid hormones?
ssx of hyperthyroidism:
Restlessness, insomnia, nervousness, weight loss, afib
What are the common complications of synthetic thyroid hormone in the elderly?
A-fib
Osteoporosis
What is the half life of T3 relative to T4?
1 day compared to 7 days for T4
What is the T4 synthetic?
Levothyroxine
What is the T3 synthetic?
Liothyronine
What is Grave’s disease?
Autoantibodies stimulate TSH receptors, and increase the production of T3 and T4
What happens to TSH levels in Grave’s disease?
Decreases
What is the effect of increased iodide? How?
hyperthyroidism can be due to underlying disease, or primary
What are the major causes of hyperthyroidism?
Grave’s
Hashimoto’s
Thyroid adenoma/carcinoma
What is a thyroid storm?
ACute episode of thyroid activity brought on by stress (surgery, infx, DKA etc)
What is the main secondary cause of hyperthyroidism?
Dysfunction of hypothalamus or pituitary
What is the general class of antithyroid agents? What are the two drugs that fall into this class? MOA?
Thioamides
Methimazole
Propylthiouracil
Inhibition of peroxidase reaction, iodine organification, and coupling of the iodotyrosine in the thyroid colloid
What is the MOA of methimazole?
Thioamides—Inhibition of peroxidase reaction, iodine organification, and coupling of the iodotyrosine in the thyroid colloid
What is the MOA of Propylthiouracil?
Thioamides—Inhibition of peroxidase reaction, iodine organification, and coupling of the iodotyrosine in the thyroid colloid
What are the side effects of the thioamides?
Rash
N/v GI distress
What is the black box warning with Propylthiouracil?
Severe Hepatitis
Why is PTU preferred in pregnancy?
More protein bound, so less likely to cross placenta
What is the drug of choice for thyroid storm? Why?
PTU because is absorbed faster
Which is more potent: methimazole or propylthiouracil?
Methimazole
What are the two Iodides that are used to treat hyperthyroidism? MOA?
Potassium iodide
Lugol’s solution
Inhibit hormone release by inhibiting proteolysis of Tgb
What is the MOA of potassium iodide?
Inhibit hormone release by inhibiting proteolysis of Tgb
What is the MOA of lugol’s solution?
Inhibit hormone release by inhibiting proteolysis of Tgb
Why are the iodides only for short term use?
Will only inhibit 2-8 weeks d/t downregulation of Na/I transporter receptor
What will happen with sudden withdrawal of iodides?
Thyrotoxicosis
What are iodides particularly good for?
Thyroid storm or preoperative thyroid problems
What are the adverse effects of Iodides?
ILI
Sore gums
Metallic tasts
What is the MOA of radioactive Iodine (I-131)?
radioactive beta rays will ablate thyroid tissue
What is the major risk of using I-131?
Total ablation of the thyroid causing hypothyroidism
Is there evidence of CA risk with using Radioactive iodine? Why or why not?
No, since it concentrates in the thyroid
What are the three anion inhibitors? MOA?
perchlorate
Pertechnetate
Thiocyanate
Inhibit Na/I transporter
What is the MOA of Perchlorate?
Inhibit Na/I transporter
What is the MOA of pertechnetate?
Inhibit Na/I transporter
What is the MOA of Thiocyanate?
Inhibit Na/I transporter
What are the adverse effects of perchlorate?
Aplastic anemia
What is the effect of amiodarone on the thyroid? What drug should be used to treat this?
Causes hypothyroidism
What beta blocker is used as an adjuvant agent for treating hyperthyroidism? Why is this used?
Propranolol
Inhibits 5’DI
Controls heart effects of hyperthyroids
What is the use of diltiazem in treating hyperthyroidism?
Controls techycardia in asthmatic
What is the use of barbiturates in treating hyperthyroidism?
Increased T4 metabolism
What is the use of Bile acid sequestrants in treating hyperthyroidism?
Increase biliary T4 excretion