Chapter 61 Drugs for Thyroid Disorders Flashcards
Thyroid Hormone (review):
What does it have effect on? What are its actions?
Profound effect on
Metabolism
Cardiac function
Growth - promotes maturation in infancy and childhood
Development
Actions
Stimulate energy use
Stimulate the heart
Promote growth and development
Triiodothyronine (T3) is what?
The active hormone
Synthetic T3: Liothyronine
Thyroxine (T4 ) is what?
The precursor to triiodothyronine (T3)
Synthetic (T4 ): Levothyroxine
What is the negative feed back loop for thyroid progression? (review)
Hypothalamus -> Thyrotropin releasing hormone (TRH) –> Anterior pituitary –> Thyroid stimulating hormone –> Thyroid T3 + T4 = Biologic affects
T3 +T4 will feedback into the anterior pituitary regarding excess (inhibition) or underproduction (stimulation)
Thyroid function tests, what 3 types? (review)
Serum thyroid-stimulating hormone (TSH)
- Screening for thyroid functions
- Elevated TSH is an indicator of hypothyroidism
Serum T4 (Free T4 or total T4)
Serum T3 (Free T3 or total T3)
Hypothyroidism is what? (review)
Deficiency of thyroid hormone caused by:
- Hashimoto’s thyroiditis disease which is a chronic autoimmune thyroiditis dz
- Iodine deficiency
- Surgical removal
Tx is lifelong
S/sx of hypothyroidism (review)
Alopecia & receding hairline
Apathy
Lethargy
Dry skin
Muscle ahces
Constipation
Cold intolerance
Anorexia
Hypothyroidism lab work is what? (review)
ELEVATED TSH
REDUCED or NORMAL Free T4
You will. also see…
Hyponatremia
Hypoglycemia
Sub-clinical; normal free T4 and slightly elevated TSH
What is the tx for hypothyroidism? What should you consider for a 60 y/o individual?
Levothyroxine (Synthroid) 1.6 mcg/kg/d and increase by 25 mcg/d every 4/6 weeks until TSH is within normal range
60 years of age, decrease dosage to 2/3 of that is needed in a younger adult)
What is the frequency of assessment for a patient that is hypothyroid that is taking Levothyroxine (Synthroid®)?
Takes 8-12 weeks for TSH levels to adjust to meds so follow up every 8-12
weeks until stable, then yearly
Is there a natural tx for hypothyroidism? What is it? What should you specifically measure for this medication?
Armour Thyroid a T3/T4 combo prescription the reason it is deemed natural is because the active ingredient is derived from thyroid of pigs
prescribed in grains not milligrams and you must measure both T3 and T4
levels.
Are brand interchangeable?
No, different brands are not interchangeable (generic ≠ brand name)
Synthetic and “natural” are never interchangeable without specific
conversion factors
Find a brand and stick with it
What is the best tx option for someone who has hypothroidism?
Synthroid® (synthetic levothyroxine) –> the best there is (Dr. Somerall’s editorial opinion)
Available in many dosages
Start low and go slow
What kind a drug interactions are there for Levothyroxine?
A lot…
Reduce absorption r/t histamine blockers, iron supplements, antacids…
Warfarin r/t increased bleeding (need to decrease warfarin dose)
Insulin dose may need increasing
Use cautiously with Catecholamines d/t dysrhythmias
What considerations are there for someone who is pregnant with hypothyroidism? What should you monitor for lab wise?
In pregnancy, thyroid binding globulin (TBG) increases throughout pregnancy
Because of increased TBG, free T4 decreases Levothyroxin (Synthroid®) when pregnant, increase dose by 50% Follow TSH every month
Following delivery, TBG will return to pre-pregnancy levels
What do you do for someone who has congenital hypothyroidism?
Replacement tx with thyroid hormones
Hyperthyroidism is caused by?
Most common in women, onset is 20-40 y/o, common presentation is Graves Disease, other causes are: toxic adenoma, tumor, high dose amiodarone
Common s/sx of hyperthyroidism?
Clubbing
Tremors
diarrhea
Heat intolerance
Bulging eyes
Flushing
Tachycardia
Enlarged thyroid
Edema
What are common laboratory diagnostics for hyperthyroidism?
Hyperthyroidism – Low TSH, High free T4/T3
Graves’ Disease – Low TSH, greater increase in T3 than in T4
Subclinical hyperthyroidism – Low TSH, but normal Free T4, T3 - goiter is commonly found through routine screening
How do you treat hyperthyroidism? Caution in? Dangerous toxic effect?
Methimazole (MMI) (Tapazole®) – first line drug by blocking synthesis of thyroid hormones
Caution in breastfeeding
AGRANULOCYTOSIS IS THE MOST DANGEROUS TOXIC EFFECT
What medication is the most preferred drug in the first trimester of pregnancy for hyperthyroidism? Why? What can you transition to after 1st trimester? Most common a/e?
Propylthiouracil (PTU) – a thiocarbamide d/t decreased risk of birth defects
Transition to methimazole
LIVER INJURY
Radioactive iodine is used for? Risk for? Monitor?
Hyperthyroidism by destroying thyroid gland (does not emit radiation outside of gland) May cause increased risk for hypothyroidism
TSH w/ ALL tx of HYPERthyroidism
Radioactive iodine is considered what in pregnancy?
Category X in pregnancy as it will cross the placenta and cause harm to the fetal thyroid
What is a thyroid storm? How do you treat it?
TRUE ENDOCRINE MEDICAL EMERGENCY
INHIBITS SYNTHESIS
Propylthiouracil (PTU) or methimazole (Tapazole) 15 q 6 hrs with the following in 1 hr…
INHIBITS RELEASE
- Lugol’s solution
- Sodium iodide
INHIBITS PERIPHERAL EFFECTS
- Propranolol (decrease sympathetic symptoms and decrease thyroxine production)
ADDITIONAL TX
Hydrocortisone w/ rapid reduction w/ improvement
NO ASA
