Thyroid Disorders Flashcards
The thyroid functions to…
1) produce thyroid hormones
2) regulate metabolism (cardiac and nervous system functions, body temperature, muscle strength, skin dryness, menstrual cycles, weight and cholesterol)
Two thyroid hormones produced by the thyroid gland are…
1) triiodothyronine (T3)
2) thyroxine (T4)
The thyroid gland is the only organ that can…
absorb iodine, which is required for the production of both hormones
Thyroid-stimulating hormone (TSH) produced by the pituitary gland stimulates the secretion of…
T3 and T4
T3 is primarily formed from…
the breakdown of T4. A small percentage (<20%) is made by the thyroid gland directly. T3 is more potent, but has a shorter half-life
Free T4 (FT4) is the unbound, active form that is…
monitored in patients with thyroid disorders
Feedback loops are used to regulate production. When the level of free T4 increases, this…
inhibits the secretion of TSH. Less TSH will lead to a decrease in T4.
Hypothyroidism is characterized by…
a deficiency in T4, and consequently, an increase in TSH
Hypothyroidism is most common in women (~80% of cases) and with increased age. The most common cause is…
Hashimoto’s disease, an autoimmune condition in which a patient’s own antibodies attack the thyroid gland
A diagnosis of hypothyroidism is made using 2 lab test results:
1) Low free T4: normal range 0.9-2.3 ng/dL
2) High TSH: normal range 0.3-3 mIU/L
Consider screening in patients> 60 y/o
Myxedema coma is a rare, but potentially fatal complication of hypothyroidism. It is a life-threatening emergency characterized by poor circulation, hypothermia, and hypometabolism. Initial treatment is…
IV levothyroxine
Major symptoms of hypothyroidism include…
Code intolerance, dry skin, fatigue, constipation, weight gain, voice changes, weakness, depression, menorrhagia (heavy period)
Drugs that can cause hypothyroidism “I TALC”:
Interferons
Tyrosine kinase inhibitors
Amiodarone (contains iodine)
Lithium
Carbamazepine
TSH is primarily tested to monitor hypothyroidism.
The TSH level and symptoms should be monitored every 4-6 weeks until levels are normal, then 4-6 months later, then yearly.
Too high of a dose in the elderly can cause…
hyperthyroidism (afib and fractures)
Serum FT4 is monitored in addition to TSH in…
1) central hypothyroidism (rare), which is a defect in pituitary production of TSH
2) when treating pregnant women
The drug of choice for the treatment of hypothyroidism is…
levothyroxine (T4). Brands: Synthroid, Levoxyl, Unithroid, Euthyrox, Tirosint, Tirosing-SOL). Keep consistent formulation and manufacturer to minimize variability.
Levothyroxine counseling points:
1) Take 60 minutes before breakfast, on an empty stomach (with water only)
2) Can take at bedtime (at least 3 hours after last meall)
Non-preferred treatments include:
1) desiccated thyroid (T3 and T4) (Armour Thyroid, Nature-Throid, NP Thyroid, Westhroid, WP Thyroid)
2) liothyronine (T3); Cytomel, Triostat
The full replacement dose of levothyroxine is…
1.6 mcg/kg (IBW)/day. Start with full dose in otherwise healthy, young (<50 years of age) patients. Start with a lower dose in milder hypothyroidism and those with comorbidities. Elderly often need 20-25% less/kg; may require <1 mcg/kg/day. If known CAD, start with 12.5-25 mcg daily.
Levothyroxine IV:PO conversion
0.75:1 (can vary by institution). Use IV immediately upon reconstitution.
Drugs that decrease levothyroxine absorption and should be spaced by 4 hours include:
1) Antacids and polyvalent cations containing Fe, Ca, Al, or Mg
2) Multivitamins (containing ADEK, folate, iron)
3) Cholestyramine
4) Orlistat (Xenical, Alli)
5) Sevelamer
6) Sucralfate
Drugs that decreased thyroid hormone levels include:
1) Estrogens
2) SSRIs
3) Liver inducers
Thyroid hormone replacement can change the [ ] or effect of these drugs..
1) increased effect of warfarin (PT/INR)
2) decreased levels of theophylline
Levothyroxine colors: Orangutans Will Vomit On You Right Before They Become Large, Proud Giants
25 mcg: orange 50 mcg: white 75 mcg: violet 88 mcg: olive 100 mcg: yellow 112 mcg: rose 125 mcg: brown 137 mcg: turquoise 150 mcg: blue 175 mcg: lilac 200 mcg: pink 300 mcg: green
Hyperthyroidism occurs when there is…
an overproduction of thyroid hormones. Free T4 (FT4) is high, TSH is low.
Symptoms of hyperthyroidism include..
1) Faster metabolism
2) Weight loss
3) Agitation, nervousness
4) Heat intolerance
5) Tremor
6) Insomnia
7) Palpitations and tachycardia
8) Light or absent periods in women
9) Exophthalmos (bulging eyes)
The most common cause of hyperthyroidism is…
Graves’ disease, which most commonly occurs in females aged 30-50 years. Also an autoimmune condition (antibodies stimulate the thyroid to make too much T4)
Drug-induced causes of hyperthyroidism include:
iodine (from diet or radiographic contrast media), amiodarone, interferons, too much levothyroxine
Treatment for hyperthyroidism can include:
1) destroying a part of the gland using radioactive iodine (RAI-131)
2) thyroidectomy surgery
3) Anti-thyroid medications (PTU, methimazole)
4) Beta-blockers for symptom control
5) Temporary effect from KI (Lugol’s solution) or saturated solution of KI (SSKI)
To control symptoms, anti-thyroid medications need to be taken for…
at least 1-3 months at high doses. Once symptoms are controlled, the dose should be decreased to prevent hypothyroidism from occurring.
Radioactive iodine can increase the risk of thyroid cancer. Potassium iodide…
blocks the accumulation of radioactive iodine in the thyroid gland and should be taken ASAP after radiation exposure. Check dosing on CDC website.
Thyroid storm is a life-threatening medical emergency characterized by decompensated hyperthyroidism. Can be precipitated by…
infection, trauma, surgery, radioactive iodine treatment or non-adherence to anti-thyroid medication.
Signs and symptoms of thyroid storm are…
fever (>103°F), tachycardia, tachypnea, dehydration, profuse sweating, agitation, delirium, psychosis, comg
Drug treatment for thyroid storm includes…
1) Anti-thyroid drug therapy (PTU is preferred); give ≥ 1 hour before iodide
2) Inorganic iodide therapy such as SSKI or Lugol’s +
3) Beta-blocker +
4) Systemic steroid +
5) Supportive treatment (cooling, fluids, etc)
Untreated maternal hypothyroidism has been associated with…
loss of pregnancy, low birth weight, premature birth and lower IQ in children
Levothyroxine is safe in pregnancy and is first-line for hypothyroidism. Ideally, start it before pregnancy. Pregnant women will require a…
30-50% increase in the dose throughout the course of their pregnancy and for several month after giving birth
Poor control of hyperthyroidism in pregnancy is associated with…
pregnancy loss, prematurity and low birth weight, thyroid storm, maternal HTN, and congestive HF. Lasting effects in baby can include seizures and neurobehavioral disorders.
Pregnancy should be postponed until..
a stable euthyroid state is reached. If a woman with hyperthyroidism becomes pregnant, she should be evaluated to see if tx can be stopped (mild disease). If treatment is needed, start anti-thyroid drugs based on the trimester
In pregnant women, the preferred drug during the first trimester is..
PTU (due to fetal toxicity with methimazole). Switch to methimazole in the 2nd and 3rd (due to lower risk of liver toxicity)
Propylthiouracil (PTU) and methimazole
BBW for PTU: severe liver injury and acute liver failure
Warnings: liver toxicity, bone marrow suppression (rare, includes agranulocytosis), DILE, vasculitis
Note: Take with food to reduce GI upset
Methimazole is the drug of choice due to…
lower risk of liver damage (except in thyroid storm and 1st trimester of pregnancy)
Monitoring for PTU and methimazole
Free T4 and T3 Q 4-6 weeks until euthyroid, TSH, CBC, LFTs and PT
Monitoring for PTU and methimazole
Free T4 and T3 Q 4-6 weeks until euthyroid, TSH, CBC, LFTs and PT. Patient must monitor for liver toxicity (abdominal pain, yellow skin/eyes, dark urine, nausea, weakness) and infection (high fever or severe sore throat)
JH is a 79-year-old female with HF and a history of MI. She is 5 feet tall and weighs 103 lbs. JH has just been diagnosed with hypothyroidism and is going to begin levothyroxine therapy. What is an appropriate dose?
25 mcg/day
A pharmacist is counseling a patient on a new medication. He tells the patient to notify her healthcare provider if she experiences a group of symptoms together, such as muscle pain, weight loss, a butterfly rash on the face, and sunburn after sun exposure. Which medication is being dispensed?
Methimazole and/or PTU can cause DILE
Which of the following drugs can cause hyperthyroidism?
iodine, amiodarone, interferon
Which best describes the MOA of methimazole?
Inhibits thyroid gland synthesis of T4 by blocking the oxidation of iodine in the thyroid gland
A medical resident asks the pharmacist for information on “desiccated thyroid” as he has heard that it is a more naturally-derived product than other treatment options. The pharmacist can tell him that it…
contains T3 and T4. It is not a first-line treatment for hypothyroidism, due to less predictable and variable responses, but some patients feel better using it than other products.
