Thyroid/Parathyroid Flashcards
Define thyroglobulin
Protein synthesized in the thyroid gland
Define Thyroxine-binding globulin (TBG)
Protein synthesized in the liver
Transports thyroid hormones in the blood
What is another name for TSH?
Thyrotropin
Lab findings in primary hypothyroidism
Elevated TSH (>4.5 mIU/L) Decreased serum free T4
Subclinical hypothyroidism lab values
Elevated TSH (>4.5 mIU/L) Normal serum free T4
When should Subclinical hypothyroidism be treated?
Iron deficiency anemia AND in patients with TSH >10
What is the most sensitive test for primary hypothyroidism and hyperthyroidism?
Serum TSH
Drugs that increase TSH
- Phenytoin
- Amiodarone
- Dopamine antagonist
- Excess estrogen or androgen
Disorders that may alter thyroid hormone lab values
- Pregnancy
- Chronic protein malnutrition
- Hepatic failure
- Nephrotic syndrome
What is the dose of a white tablet Levothyroxine
(Synthoid)?
50 mcg
What is the dosing of Levothyroxine? Half life?
Daily dosing
Half life= 7 days
When you change a dose of levothyroxine, when do you recheck a TSH and why?
Recheck TSH @ 6 weeks
Reaches steady state after 4-5 half lives
What can impair/reduce Levoythyroxine (T4) absorption?
- Food (take on empty stomach)
- H2 blockers and PPI’s
- Mucosal dz’s
Drugs that increase non-deiodinative T4 clearance
- Rifampin
- Carbamazepine
- Phenytoin
List the Synthetic T3 drug
Liothyronine
Cytomel
What is unique/disadvantage about Synthetic T3?
Rapid onset= Burst of energy
Short half life
Some is delivered too much to tissue than what is appropriate
List Synthetic T4:T3 (4:1) ratio drug
Liotrix
Throlar
Why does Synthetic T4:T3 LACK therapeutic rationale?
T4 is converted to T3 peripherally
What dose in the treatment of hypothyroidism do most patients require once they have reached steady state?
1.7 mcg/kg/day
What weight gives you a better estimate of a patient’s dose requirement?
Ideal Body Weight (IBW)
What it is the initial dose of Levothyroxine in young pt’s with long-standing dz and pt’s >45 WITHOUT known cardiac dz? When is it increased? Amount?
Initial dose= 50 mcg daily
Increased to 100 mcg after ONE month
What is the recommended initial daily dose for older patients OR those with known cardiac disease. When is is titrated up? Amount?
25 mcg per day
Titrated upward in increments of 25 mcg at monthly intervals
What percentage of pregnant women does the thyroxine dose requirement increase?Why?
75%
Fetus is very reliant on T4 during the 1st trimester
What can excessive doses of thyroid hormone lead to?
- Heart failure
- Angina pectoris
- MI
What levothyroxine tablet is the least allergenic?
0.05 mg (50 mcg)= White tablet
Dye FREE
Result of hyperthyroidism in bones?
Hyperremodeling of cortical and trabecular bone= Reduced bone density=Increased risk of fx
TSH-Suppressive Levothyroxine Therapy Indications
- Nodular thyroid dz and diffuse goiter: Suppress TSH to low-normal levels (0.5-1)
- Hx of thyroid irradiation
- Thyroid CA: Higher risk pt’s (TSH <0.1), Lower-risk pt’s (0.1-0.5)
What drugs can hypothyroidism effect the distribution?
- Digoxin-Higher serum values
2. Warfarin: Decreases sensitivity d/t lower metabolism of Vitamin K
What are the cardinal si/sx’s in HYPERthyroidism?
- Weight loss
2. Increased appetite
What si/sx’s are specific to Grave’s disease (Hypothyroidism)?
- Exopthalmos
2. Pretibial Myxedema
What is first-line hyperthyroidism treatment in children, adolescents, and in pregnancy?
Antithyroid drugs:
- Propothyrouracil (PTU)
- Methimazole (MMI)*
Propothyrouracil (PTU) and Methimazole (MMI) MOA
Inhibit coupling of monoiodotyrosine and diiodotyrosine to form T4 and T3
How many weeks does it take for sx’s to diminish and circulating thyroid hormone levels return to normal?
4-8 weeks
When should changes in PTU and MMI doses for each drug be made?
Monthly
What is the MC ADE of PTU and MMI?
Hepatoxicity
Other PTU and MMI. ADE’s?
- Rash
- Leukopenia (benign)
- Agranulocytosis
- Arthralgias and a lupus-like syndrome
When is the ONLY time that PTU is considered a first-line drug treatment? Why?
Frist Trimester of pregnancy
MMI teratogenic effects outweighs that of PTU-associated hepatoxicity
When should Potassium iodide be administered?
7-14 days preoperatively (general surgery)
As an adjunct to radioactive iodine, when should saturated solution potassium iodide (SSKI) be administered? Why?
3-7 days AFTER RAI treatment
Allow that radioactive iodide to concentrate in the thyroid
Iodide ADE’s
- Salivary gland swelling
2. “Iodism”: Metallic taste, burning mouth/sore throat,, sore teeth/gums; gynecomastia
What can you prescribe for symptom relief in hyperthyroidism?
Propranolol
What is the advantage of radioactive iodine? When is this the best treatment option?
Hyperthyroidism cure
Best treatment for toxic nodules and toxic multinodular goiter
What are the disadvantage of radioactive iodine?
- Permanent hypothyroidism almost inevitable
2. Pregnancy must be deferred for 6–12 months; no breast-feeding
When is surgery for hyperthyroidism the best option?
- In pregnancy if major S/E from antithyroid drugs
- Coexisting suspicious nodule present
Lab findings in hypoparathyroidism
HYPOcalcemia
HYPERphosphatemia
HYPERcalciruia
What is crucial for PTH secretion and activation of the PTH receptor?
Magnesium
hypoparathyroidism treatment
- Oral calcium carbonate
- Calcitrol (Vitamin D 1,25)
- Phosphate binders: If high calcium-phosphate
Define primary hyperparathyroidism
Intrinsic parathyroid gland dysfunction resulting in excessive secretions of PTH with a lack of response to feedback inhibition by elevated calcium
Define secondary hyperparathyroidism
Excessive secretion of PTH in response to hypocalcemia
Causes for secondary hyperparathyroidism?
- Vitamin D deficiency
2. Renal failure
What PTH level suggest primary hyperparathyroidism?
High PTH (>3.0 pmol/L)
What PTH level suggest non-PTH-mediated hypercalcemia?
Low PTH (<3.0 pmol/L)
What is the curative treatment for primary hyperparathyroidism?
Surgery
Secondary hyperparathyroidism treatment
- Calcium replacement
- Vitamin D analogues: paricalcitol and calcitriol
- Phosphorus-binding agents: sevelamer
- Calcimimetic: cinacalcet)
What are the advantages of Antithyroid drugs?
- Noninvasive*
2. Low risk of permanent hypothyroidism
What are the disadvantages of Antithyroid drugs?
Low cure rate (Avg=40-50%)
