Chapter 45 - Thyroid disorder Flashcards
The thyroid gland produces thyroid hormones, which regulate:
1- metabolism
2- cardiac and nervous system functions,
3- body temperature,
4- muscle strength,
5- skin dryness,
6- menstrual cycles,
7- weight and
8- cholesterol levels.
1) triiodothyronine:
2) thyroxine:
1) T3
2) T4
thyroid is the only organ that can absorb:
iodine
1- T3 is primarily formed from:
2- Who is more potent? who has a longer 1/2 life?
3- Thyroid hormone production is regulated by:
4- TSH is secreted by:
1- the breakdown of T4.
A small percentage (< 20%) is produced by the thyroid gland directly.
2- T3 is more potent than T4 but has a shorter half-life.
3- thyroid-stimulating hormone (TSH), also referred to as thyrotropin.
4- the pituitary gland, which is located in the brain and regulates growth and development.
What is the negative feedback loop?
- When the level of circulating (free) T4 increases, it inhibits the secretion of TSH.
- Less TSH will lead to a decrease in T4 production.
what form of T4 do you monitor in patients with thyroid disorder?
free unbound t4
hypothyroidism:
t4 level?
tsh level?
t4 low
tsh is high
hypothyr occur most commonly in:
- females (80% of cases)
- older age
Sx of hypothyroidism:
1- cold intolerance
2- dry skin
3- fatigue
4- muscle cramps
5- voice changes
6- constipation
7- weight gain
8- goiter (can also be for low iodine intake)
9- myalgia
10- weakness
11- depression
12- bradycardia
13- coarse hair/ loss hair
14- menorrhagia (heavy periods)
15- memory & mental impairment
Most common cause of hypothyroidism is:
Hashimoto’s dx
- autoimmune dx
- pt’s own antibodies attacks thyroid gland
Drugs that can cause hypothyroidism:
- Interferons*
- Tyrosine kinase inhibitors (e.g.,sunitinib)
- Amiodarone*
- Lithium
- Carbamazepine
- Oxcarbazepine
- Eslicarbazepine
- Phenytoin
“ITALC OEP
- Can also cause hyperthyroidism
Conditions that can cause hypoth
1- Iodine deficiency
2- Pituitary failure (secretes TSH)
3- Surgical removal of thyroid gland
4- Congenital hypothyroidism
5- Thyroid gland ablation with radioactive iodine
6- External irradiation
7- Hashimoto’s Dx
1- an uncommon but life threatening condition caused by untreated hypothyroidism?
2- How to treat?
1- Myxedema Coma
2- IV Levothyroxine
3- It is a life threatening emergency characterized by poor circulation, hypothermia, hypometabolism.
A diagnosis of hypothyroidism is made using two laboratory test results:
■ Low free T4: Normal range 0.9 - 2.3 ng/dL
■ High TSH: Normal range 0.3- 3 m lU/L
When should you consider screening?
In patients > 60 years old
what are the 3 tests you do for thyroid function?
- TSH
- FT4
- Total T3
What is the primary test to monitor thyroid function in those receiving thyroid hormone replacement with drug treatment?
- TSH
- FT4 occasionally ordered with TSH
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 thyroid hormone replacement dose in elderly patients can cause:
- Atrial fibrillation
- Fractures
what is central hypothyroidism? And what do you monitor in it?
- A defect in pituitary production of TSH
- It is a rare condition
- Serum FT4 is monitored in addition to TSH
Goals of ttmt:
- resolve symptoms,
- achieve euthyroid state (i.e., normal levels of thyroid hormones)
- avoid over-treatment; excessive doses of thyroid hormone will cause hyperthyroidism.
What is the drug of choice in hypoth
Levothyroxine (T4)
make sure to use a consistent preparation (same manufacturer and formulation)
Foods high in iodine
- dairy
- seafood
- meat
- some breads
Levothyroxine Brand names:
- Synthroid
- Levoxyl
- Unithroid
- Euthyrox
- Tirosint
- Tirosint-SOL
Full replacement dose of levothyroxine in hypothyroidism:
1.6 mcg/Kg/day
use IBW
- Start with full replacement dose in otherwise healthy, young(< 50 years of age) patients with markedly inc TSH
Start with partial replacement dose of levoth in:
- milder hypothyroidism
- those with comorbidities
If known CAD, start levoth dose of:
12.5-25 mcg daily
Elderly patients often need a levoth dose of
20 - 25 % less per Kg
May require < 1 mcg/kg/day
Levothyroxine PO administration
- take with water
- at the same time each day for consistent absorption,
- at least 60 minutes before breakfast
- or at bedtime (at least three hours after the last meal)
25 mcg color
orange
50 mcg color
white
75 mcg color
Violet
88 mcg color
olive (light green)
100 mcg color
yellow
112 mcg color
rose
125 mcg color
brown
137 mcg color
turquoise
150 mcg color
blue
175 mcg color
lilac
200 mcg color
pink
300 mcg color
green
mnemonic for color codes of PO levothyroxine tabs
Orangutans Will Vomit On You Right Before They Become Large, Proud Giants.
orange - 25
white - 50
violet - 75
olive - 88
yellow - 100
rose
brown
turquoise - 137
blue - 150
liliac - 175
pink - 200
green - 300
Levothyroxine IV
IV to PO ratio is:
- 0.75 : 1
- use immediately upon reconstitution
Levothyroxine oral solution should you dilute it? and with what?
how should you store it?
- Can be given undiluted or diluted (in water only);
- store in original container
Thyroid, Desiccated USP brand names
- T3 andT4
- Armour Thyroid
- Nature-Throid
- NP Thyroid
- Westhroid
- WP Thyroid
Thyroid, Desiccated USP dose
- Start 15-30 mg daily (15 mg in cardiac disease);
- titrate in 15 mg increments
- Usual dose is 60-120 mg daily
Natural porcine-derived thyroid that contains both T3 and T4; less predictable potency and stability
Liothyronine
- active ing
- brands
- dose?
- T3
- Cytomel,
- Triostat
- Tablet, injection
- Start 25 mcg daily; titrate in 12.5-25 mcg increments
- Usual dose is 25-75 mcg daily
- Shorter half-life causes fluctuations in T3 levels
Liotrix
brands
dose
- T3 and T4 in 1:4 ratio
- Thyrolar
- Tablet
- Start 25 mcg levothyroxine/6.25 mcg liothyronine daily
- Usual dose is 50-100 mcg levothyroxine/ 12.5-25 mcg liothyronine
BBW of hypothy ttmt:
- Ineffective and potentially toxic when used for obesity or weight reduction, especially in euthyroid patients;
- high doses can cause serious, life-threatening toxic effects, particularly when used with some anorectic drugs (e.g., sympathomimetic amines)
CI of hypothy ttmt:
Uncorrected adrenal insufficiency
warning regarding hypothy ttmt and CVD and BMD
- dec dose in cardiovascular disease (chronic hypothyroidism predisposes to coronary artery disease),
- dec bone mineral density which can lead to osteoporosis
Hyperthyroid symptoms that can occur when the dose is too high:
- inc HR
- palpitations
- sweating
- weight loss
- arrhythmias
- irritability
Monitoring with hypothy ttmt:
- TSH levels and clinical symptoms every 4-6 weeks until levels are normal, then 4-6 months later, then yearly;
- Serum FT4 in select patients (pregnant …)
T/F:
1) T4 are highly protein bound
2) Dose Increase may be necessary as the patient ages
t: Highly protein bound (> 99%)
f: Dose reduction may be necessary as the patient ages
If the patient got pregnant or is breastfeeding, do you need to increase or decrease their dose of levothyroxine?
increase
Drugs that dec levothyroxine absorption:
o Antacids and polyvalent cations containing iron, calcium, aluminum or magnesium, multivitamins (containing ADEK, folate, iron), cholestyramine, orlistat (Xenical, Alli), sevelamer and sucralfate: separate doses by four hours from thyroid replacement therapy.
o Sodium polystyrene sulfonate and patiromer (Veltassa):separate doses by three hours from thyroid replacement therapy.
o Lanthanum: separate doses by two hours from thyroid replacement therapy.
drugs that dec thyroid hormone levels.
- Estrogen,
- SSRIs
- hepatic inducers
drugs that can dec the effectiveness of levothyroxine by dec the conversion of T4 to T3.
- Beta-blockers,
- amiodarone,
- propylthiouracil (PTU)
- systemic steroids
Thyroid hormone is highly protein bound (> 99%). Drugs can cause protein-binding site displacement (e.g., …).
phenytoin
Hyperthyroidism:
- overactive thyroid or thyrotoxicosis
- occurs when there is over-production of thyroid hormones.
- FT4 is high, TSH is low
Sx of hyperthy
- Heat intolerance or increased sweating
- Weight loss
- Agitation, nervousness, irritability, anxiety
- Palpitations and tachycardia
- Fatigue and muscle weakness
- Frequent bowel movements or diarrhea
- Insomnia Tremor
- Thinning hair Goiter (possible)
- Exophthalmos (protrusion of the eyeballs), diplopia
- Light or absent menstrual periods
causes of hyperthy
1) Graves dx
- most common cause
- most commonly in women 30 - 50 yr
- autoimmune disorder,
- the antibodies stimulate the thyroid to produce too much T4.
2) Thyroid nodules and thyroiditis
- Less common
- inflam of thyroid
3) Drug-induced causes of hyperthyroidism:
- iodine,
- amiodarone
- interferons.
4) Excess iodine increases the synthesis and release of thyroid hormone. Iodine-induced hyperthyroidism can be due to excess iodine in the diet or exposure to radiographic contrast media.
5) Excessive doses of thyroid hormone can cause hyperthyroidism.
ttmt of hyperthy
1) antithyroid medications,
2) destroying part of the gland via radioactive iodine (RAI-131)or surgery.
- RAI- 131 has historically been considered the preferred treatment in Graves’ disease, but all three treatment options are effective and relatively safe.
3) With any option, the patient can be treated with beta-blockers first for symptom control (to reduce palpitations, tremors and tachycardia).
4) Propylthiouracil (PTU) or methimazole can be used as a temporary measure until surgery is complete.
It takes — of treatment with antithyroid medications at high doses to control symptoms.
Once symptoms are controlled, the dose should be — to prevent hypothyroidism from occurring.
1- 3 months
reduced
Thionamides moa
Inhibits synthesis of thyroid hormones by blocking the oxidation of iodine in the thyroid gland;
PTU also inhibits peripheral conversion of T4 to T3
Propylthiouracil (PTU)
Tablet
50-150 mg Q8H initially until euthyroid
(higher doses for more severe hyperthyroidism),
followed by dose reduction
BOXED WARNINGS (PTU)
1) Severe liver injury and acute liver failure
2) Pregnancy: PTU preferred in 1’’ trimester (due to increased risk of fetal abnormalities from methimazole)
Warning with thionamides
WARNINGS
- Hepatotoxicity,
- bone marrow suppression (rare, includes agranulocytosis),
- drug-induced lupus erythematosus (DILE),
- vasculitis
SE with thionamides
SIDE EFFECTS
- GI upset,
- headache,
- rash (exfoliative dermatitis, pruritus),
- fever,
- constipation,
- loss of taste/taste perversion,
- lymphadenopathy,
- bleeding
monitoring with thionamides
MONITORING
- FT4 and T3 every 4-6 weeks until euthyroid,
- TSH,
- CBC,
- LFTs
- PT
Patient must monitor for
1) liver toxicity:
- abdominal pain,
- yellow skin/eyes,
- dark urine,
- nausea,
- weakness)
2) infection:
- high fever
- severe sore throat
thionamides: take with or without food?
Take with food to reduce GI upset
what is the drug of choice for hyperthy?
when is the other option preferred?
Methimazole is the drug of choice (due to a lower risk of liver damage)
except in certain situations:
PTU is preferred in thyroid storm and if methimazole is not tolerated
Pregnancy: PTU is preferred in the 1’’ trimester; methimazole can be used in the 2nd and 3rd trimesters (to dec the risk of liver toxicity from PTU)
iodides moa
Iodides - temporarily inhibit secretion of thyroid hormones;
T4 and T3 levels will be reduced for several weeks but effect will not be maintained
Potassium iodide and iodine solution
Oral solution
Lugol’s Solution
Preparation for thyroidectomy:
5-7 drops Q8H for 10 days prior to surgery (off-label)
Saturated solution of potassium iodide
Oral solution
SSKI, ThyroSafe
Preparation for thyroidectomy:
1-2 drops Q8H for 10 days prior to surgery (off-label)
CI of iodides:
- Hypersensitivity to iodide or iodine,
- dermatitis herpetiformis,
- hypocomplementemic vasculitis,
- nodular thyroid condition with heart disease
iodides SE, Monitoring, notes
SIDE EFFECTS
- Rash,
- metallic taste,
- sore throat/gums,
- GI upset,
- urticaria,
- hypo/hyperthyroidism with prolonged use
MONITORING
- Thyroid function tests,
- s/sx of hyperthyroidism
NOTES
- Dilute in a glassful of water, juice, or milk;
- take with food or milk to dec GI upset
- SSKI is also used as an expectorant
POTASSIUM IODIDE USE AFTER EXPOSURE TO RADIATION
Potassium iodide (KI) blocks the accumulation of radioactive iodine in the thyroid gland, thus preventing thyroid cancer.
Potassium iodide should be taken as soon as possible after radiation exposure on the advice of public health or emergency management personnel only.
The correct dose must be used; higher doses do not offer greater protection.
Refer to the CDC website for age-specific dosing based on the duration of radiation exposure.
Iodized salt and foods do not contain enough iodine to block radioactive iodine and are not recommended.
thyroid storm sx
- life threatening medical emergency
1) Fever (> 103°F)
2) Agitation
3) Tachycardia
4) Delirium
5) Tachypnea
6) Dehydration
7) Profuse sweating
8) Psychosis
10) Coma
DRUG TREATMENT of thyroid storm
DRUG TREATMENT
■ Antithyroid drug therapy (PTU is preferred; 500 - 1,000 mg loading dose, then 250 mg PO Q4H)
PLUS
■ Inorganic iodide therapy such as:
- SSKI 5 drops (in water or juice) PO Q6H or
- Lugol’s Solution 4- 8 drops PO Q6- 8H
PLUS
■ Beta-blocker
(e.g., propranolol 40- 80 mg PO Q6H)
PLUS
■ Systemicsteroid
(e.g.,dexamethasone 2- 4mg PO Q6H)
PLUS
■ Aggressive cooling with acetaminophen and cooling blankets and other supportive treatments
(e.g., antiarrhythmics, insulin, fluids, electrolytes)
The antithyroid drug should be given >= 1hour before iodide to block synthesis of thyroid hormone.
PTU tablets can be crushed and administered through an NGtube if needed.
PREGNANCY AND HYPOTHYROIDISM
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 the recommended treatment.
Pregnant women treated with thyroid hormone replacement will require a 30 - 50% increase in the dose throughout the course of their pregnancy and for several months after giving birth.
Aggressive control of hypothyroidism in pregnancy is recommended.
Treatment should ideally be started prior to the pregnancy.
PREGNANCY AND HYPERTHYROIDISM
Poor control of hyperthyroidism in pregnancy is associated with:
- pregnancy loss,
- prematurity and low birth weight,
like hypothyroidism, as well as
- thyroid storm,
- maternal hypertension and
- congestive heart failure.
There can be lasting effects in the baby, including
- seizure disorders 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 treatment can be stopped (mild disease).
If treatment is needed, it should be with antithyroid drugs based on the trimester.
For the first trimester, PTU should be used (due to fetal toxicity with methimazole).
After that, the decision is individualized, as both PTU and methimazole carry potential risks.
Historically, the patient would be switched to methimazole for the remainder of the pregnancy.
PREGNANCY AND HYPERTHYROIDISM
Poor control of hyperthyroidism in pregnancy is associated with:
- pregnancy loss,
- prematurity and low birth weight,
like hypothyroidism, as well as
- thyroid storm,
- maternal hypertension and
- congestive heart failure.
There can be lasting effects in the baby, including
- seizure disorders 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 treatment can be stopped (mild disease).
If treatment is needed, it should be with antithyroid drugs based on the trimester.
For the first trimester, PTU should be used (due to fetal toxicity with methimazole).
After that, the decision is individualized, as both PTU and methimazole carry potential risks.
Historically, the patient would be switched to methimazole for the remainder of the pregnancy.
