Most severe form of hypothyroidism: - Appear to have edema beneath skin - Can cause coma - Hypothermia - Altered mental status

Thyroid Flashcards by Dave Shields

What drugs block conversion of T4 to T3?

Beta-blockers
Steroids
Amiodarone

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What three hormones are secreted by the thyroid?

T3: Triiodothyronine-9%
T4: Thyroxine-90%
Calcitonin

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What makes up T3?

MIT + DIT

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What makes up T4?

DIT + DIT

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Which is more potent, T3 or T4?

T3 is 3x more potent

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What chemical converts iodide to iodine?

Peroxidase

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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

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What is organification?

Peroxidase catalyzes iodination of tyrosine on thyroglobulin forming MIT and DIT

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What drugs block organification and coupling of thyroid hormones?

Sulfonylureas

Thionamides

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What chemicals can block proteolytic cleavage of thyroid hormones from thyroglobulin and thus their release?

High doses of iodide

Lithium

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What chemicals are thyroid hormones transported on via plasma?

Thyroid binding globulin (TBG)
Albumin
Thyroid-binding Pre-albumin (TBPA)

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At what TSH level should we treat?

> 10: L-thyroxine

<10: children; pregnant or infertile; symptomatic; thyroid autoantibodies

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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

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Hypothyroidism effects on drugs?

Digitalis: decreased volume of distribution
Insulin: impaired degradation
Warfarin: decreased breakdown of clotting factors

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Causes of primary hypothyroidism?

Hashimotos’s disease
Iatrogenic: radioactive iodine, thyroidectomy
Iodine deficiency: not common

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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

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What is myxedema?

Most severe form of hypothyroidism:

Appear to have edema beneath skin
Can cause coma
Hypothermia
Altered mental status

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What are ADRs of Levothyroxine?

Arrhythmias
Tachycardia
Angina, sweating, weight loss
Restlessness, Osteoporosis

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What drugs alter the absorption of levothyroxine?

Cholestyramine
Ferrous sulfate
Sucralfate
Aluminum hydroxide
Take thyroxine 2 hrs. before or 4 hours after

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What drugs increase metabolism of levothyroxine?

Rifampin
Phenytoin
Carbamazepine

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What effect do oral contraceptives/estrogen have on levothyroxine?

Increase binding to globulin reducing free thyroid

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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?

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?

1. Agranulocytosis-get baseline WBC count and stop if pt. gets fever or sore throat 2. Hepatotoxicity-same as above 3. 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