Thyroid Flashcards
What drugs block conversion of T4 to T3?
Beta-blockers
Steroids
Amiodarone
What three hormones are secreted by the thyroid?
T3: Triiodothyronine-9%
T4: Thyroxine-90%
Calcitonin
What makes up T3?
MIT + DIT
What makes up T4?
DIT + DIT
Which is more potent, T3 or T4?
T3 is 3x more potent
What chemical converts iodide to iodine?
Peroxidase
What chemicals can block iodide uptake into thyroid cells?
- Inorganic ions: thiocyanate and perchlorate
- Cardiac glycosides: by inhibiting K accumulation
- Bromine, fluorine, and lithium: block transport of iodide into thyroid
What is organification?
Peroxidase catalyzes iodination of tyrosine on thyroglobulin forming MIT and DIT
What drugs block organification and coupling of thyroid hormones?
Sulfonylureas
Thionamides
What chemicals can block proteolytic cleavage of thyroid hormones from thyroglobulin and thus their release?
High doses of iodide
Lithium
What chemicals are thyroid hormones transported on via plasma?
Thyroid binding globulin (TBG)
Albumin
Thyroid-binding Pre-albumin (TBPA)
At what TSH level should we treat?
> 10: L-thyroxine
<10: children; pregnant or infertile; symptomatic; thyroid autoantibodies
What are some negative effects of sub-clinical hypothyroidism?
Increased risk of coronary heart disease
Placental abruption risk
Preterm delivery risk
Women with thyroid autoantibodies at risk of abortion
Hypothyroidism effects on drugs?
- Digitalis: decreased volume of distribution
- Insulin: impaired degradation
- Warfarin: decreased breakdown of clotting factors
Causes of primary hypothyroidism?
- Hashimotos’s disease
- Iatrogenic: radioactive iodine, thyroidectomy
- Iodine deficiency: not common
What are some risk factors for hypothyroidism?
Post-partum women
Autoimmune endocrine disorders: DM type 1, adrenal insufficiency
Other conditions: celiac disease, vitiligo, MS, pernicious anemia, Down’s syndrome
What is myxedema?
Most severe form of hypothyroidism:
- Appear to have edema beneath skin
- Can cause coma
- Hypothermia
- Altered mental status
What are ADRs of Levothyroxine?
- Arrhythmias
- Tachycardia
- Angina, sweating, weight loss
- Restlessness, Osteoporosis
What drugs alter the absorption of levothyroxine?
- Cholestyramine
- Ferrous sulfate
- Sucralfate
- Aluminum hydroxide
- Take thyroxine 2 hrs. before or 4 hours after
What drugs increase metabolism of levothyroxine?
Rifampin
Phenytoin
Carbamazepine
What effect do oral contraceptives/estrogen have on levothyroxine?
Increase binding to globulin reducing free thyroid
Indications for Liothyronine sodium?
- Initial therapy for myxedema and myxedema coma
- Short-term suppression of TSH before thyroid cancer surgery
- Patients with 5’-deiodinase deficiency who cannot convert T4 to T3
What is liotrix?
4: 1 Levo/Liothyronine
- Not more effective than Levo by itself
How do we define subclinical hyperthyroidism?
- TSH<0.1
- T4 normal
What disease causes a diffuse toxic goiter?
Grave’s disease
What are some causes of hyperthyroidism?
- Grave’s disease
- Painless thyroiditis
- TSH-secreting adenoma
- Human chorionic gonadotrophin-secreting tumor
What is the most common cause of hyperthyroidism?
Grave’s disease:
- Diffuse thyroid
- Myxedema
- Thyroid acropachy
- IgG antibodies against TSH receptors
In Grave’s disease is there more T3 released or T4 released?
T3
Hyperthyroidism in pregnancy is almost caused by what?
Grave’s disease
What is the drug of choice for hyperthyroidism in pregnancy?
PTU
Treatment for hyperthyroidism during pregnancy?
- Radiation of thyroid then supplement thyroid hormones
- PTU
What drugs for hyperthyroidism are contraindicated in pregnancy?
RAI
Methimazole
What characterizes a thyroid storm?
Severe thyrotoxicosis, high fever (over 103), tachycardia, tachypnea, dehydration, delirium-coma, N/V, diarrhea
What is the treatment for thyroid storm?
Methimazole plus:
Anti-adrenergics
Corticosteroids
What drugs are Thioamides?
PTU
Methimazole
How do thioamides work?
Block thyroid hormone synthesis at substrates for iodination by thyroid peroxidase
-PTU also inhibits conversion of T4 to T3`
What is drug of choice for hyperthyroidism for non-pregnant women?
RAI
Which drug is more potent: PTU or Methimazole?
Methimazole is 10x more potent
Most serious ADRs of Thioamides?
- Agranulocytosis-get baseline WBC count and stop if pt. gets fever or sore throat
- Hepatotoxicity-same as above
- Vasculitis-drug-induced lupus or antineutrophil
- Can cause thyroid enlargement
Most frequent ADRs with Thioamides?
Rash, arthralgia, cholestatic jaundice, lymphadenopathy, fever, psychosis, alopecia
How do potassium iodines work?
Inhibition of TH secretion:
- Blocks conversion of T4 to T3
- Organification
- Dilutes effects of iodine in blood and loads it in gland
- Also blocks vascularity and size of gland
Indications for iodines?
- Pre-op for thyroidectomy (7-14 days)
- Used after RAI (3-7 days) to allow RAI to concentrate in gland
Contraindications for iodines?
Do not use in breastfeeding women; can cause goiter in infants
How do we administer iodines?
10-14 days before partial thyroidectomy w/ Methimazole or PTU; cannot give long-term because it will lose it effectiveness
ADRs for iodines?
Hypersensitivity reaction
Lacrimation, conjunctivitis, laryngitis, thyrotoxicosis in patients w/ nontoxic goiter, drug fever, rash, metallic taste
What are indications for radioiodine?
-Grave’s disease, toxic autonomic nodules, toxic multinodular goiters
Major disadvantages of radioactive thyroid?
- Hypothyroidism in most patients; usually women; can occur months or years after
- African Americans more likely to be resistant to RAI-multiple doses
MOA for lithium?
Inhibits incorporation of iodine into thyroid gland; inhibits release
What do steroids help with?
-Thyroiditis or thyroid storm
Decrease thyroid function
Decrease immune response
What drug causes the Wolff-Chaikoff effect?
Iodine
What patients should not receive a thyroidectomy?
Patients w/ low RAI uptake
What drugs should we give before a thyroidectomy?
PTU or Methimazole
What are some complications for thyroidectomy?
Hyperthyroidism
Hypothyroidism
Hypoparathyroidism
