Thyroid & Parathyroid Flashcards
Where is T4 and T3 made?
T4 is made in the thyroid gland only!
T3 is made in the thyroid gland (20%) and in the periphery when T4 is broken down
How much of T4 and T3 are protein bound?
about 99%
What labs would you expect to see in a primary hypothyroidism case?
- Elevated TSH (>4.5)
- Decreased T4
When and how often do TSH levels need to be monitored in pregnancy?
monthly during 1st trimester
When do TSH levels need to be checked postpartum?
check TSH 6 weeks after giving birth
Name some drugs that can cause low T4 or T3
- Corticosteroids
- Naproxen
- Salicylates in large doses
What is the drug of choice for hypothyroidism?
Levothyroxine* (ex. Levothroid, Synthroid, Levoxyl)
-half-life is 7 days, so daily dosing
When you change dose of levothyroxine, when do you recheck TSH?
4-6 weeks (because that’s when steady state will occur 4-5 half-lives)
What are two important considerations for levothyroxine absorption?
- Food impairs absorption
- H2 receptor blockers and PPI can reduce absorption
What is the average maintenance dose of levothyroxine for most adults?
125 mcg/day
What is the name of T3 to treat hypothyroidism?
Liothyronine, Cytomel, Liotrix, Thyrolar (expensive)
Armour Thyroid, Naturethroid
desiccated pork thyroid gland. inexpensive. No recommended for treating hypothyroidism.
Hypothyroidism treatment Pearls
- Most patients will require about 1.7mcg/kg/day once they reach steady state
- Dose requirement may be better estimated based on ideal body weight (rather than actual)
- Young patients with longstanding disease or over 45 without known cardiac disease: start on 50mcg daily. Increase to 100mcg daily after 1 month
What is the normal starting dose for young patients/patients over 45 without cardiac disease?
- Start on 50mcg/day
2. Increase to 100mcg/day after 1 month
What is the most appropriate dose to start an older patient with hypothyroidism on?
25 mcg/day
Titrate up to best dose by 25mcg increments every month (to prevent stress on the cardiovascular system)
How does pregnancy affect thyroxine dose requirement, generally?
pregnant patients will often need increased thyroxine dose
due to placental deiodinase degradation, transfer of T4 to fetus
Name two important drug-disease interactions with hypothyroidism
- Increased digoxin levels
2. Decrease effectivness of Warfarin (may need to increase dose)
What are 3 major complications of overreplacing thyroid hormone?
- heart failure
- anginapectoris
- myocardial infarction
Which levothyroxine tablet is the least allergenic?
50mcg (due to lack of dye and fewer excipients)
Hyperthyroidism can have what effect on the bones?
hyperremodeling of cortical and trabecular bone –> leading to reduced density and increased risk of fracture
Ideally, how is Levothyroxine taken?
in the morning, 1 hour before breakfast
avoid taking ferrous sulfate, PPI, calcium carbonate, bile acid resins for 4 hours after taking thyroid medication
What are two physical exam findings only seen in Grave’s disease?
- Exopthalmos
2. Pretibial myxedema
What is the 1st line treatment in hyperthyroidism for children, adolescents, and pregnant women?
antithyroid drugs
Thiourea drugs
Propothyrouracil (PTU)
Methimazole (MMI)
How do thiourea drugs work for hyperthyroidism?
they inhibit the formation of T4 and T3
When is the best time to change dose for the thiourea drugs?
monthly
Thiourea drugs (propothrouracil and Methimazole) ADEs
- Benign transient leukopenia
- Agranulocytosis (within the first 3 months of therapy)
- Arthralgias and lupus-like syndrome
- Hepatotoxicity
What is the drug of choice for hyperthyroidism in 1st trimester of pregnancy?
Propothyrouracil (PTU)
Iodides: MOA
-used for hyperthyroidism (Graves’ disease)
- blocks release of thyroid hormone (so it is stored inside the gland)
- Inhibits biosynthesis of thyroid hormone
- Decreases size and vascularity of gland
When would you expect to see improvement with Iodides?
2-7 days
When should potassium iodide be given preoperatively?
7-14 days
Iodides ADEs
- Salivary gland swelling
- “iodism” (metallic taste, burning mouth/throat, sore teeth/gums, gynecomastia)
What is the adjunct therapy of choice for hyperthyroidism?
Propranolol
What is primary therapy for thyrotoxicosis associated with thyroiditis?
Propranolol
Propranolol (adrenergic blockers) contraindications
- decompensated heart failure
- sinus bradycardia
- MOAIs, or TCA
- spontaneous hypoglycemia
caution in asthma**
What is the best treatment for toxic nodules and toxic multinodular goiters?
Radioactive iodine
Radioactive iodine: disadvantages
- permanent hypothyroidism
- pregnancy MUST be deferred for 6-12 months; no breast feeding
Thyroid removal surgery
- Complications: recurrent laryngeal nerve damage, hypoparathyroidism
- costly $$$
- Can be done in pregnancy if the oral drugs don’t work well
Acute hypoparathyroidism: signs
Hypocalcemia –> tetany (muscle cramps, paresthesias of hands and feet) or (carpopedal spasm, layngospasm, heart failure, seizure, stridor)
Hypoparathyroidism: treatment
- oral cacium carbonate
- Vitamin D
- Phosphate binders (maybe)
- Thiazide diuretics + low salt diet to prevent loss of calcium
Primary Hyperparathyroidism: treatment
- surgery is curative
- bisphosphonates to avoid bone turnover and help maintain bone density (if awaiting surgery, or unable to have surgery)
When are Thyroglobulin (Tg) levels primary used?
thyroid cancer
- effectiveness of treatment
- monitor for recurrence
