Thyroid Drugs Flashcards
What are the symptoms of hypothyroidism?
Fatigue, cold intolerance, weight gain despite lack of appetite, irregular menses, nonpitting edema (myxedema), high blood cholesterol, constipation, decreased deep tendon reflex, dry skin, elderly dementia
How do you treat hypothyroidism long term and what is the side effect of this drug?
Levothyroxine (T4, consistent potency, long duration of action); ADRs include tachycardia, heat intolerance, tremors
What are the symptoms of hyperthyroidism (Thyrotoxicosis)?
Excitability, Intolerance to heat, Increased sweating, Mild to extreme weight loss, Varying degrees of diarrhea, Muscle weakness, Nervousness or other psychic disorders, Extreme fatigue but inability to sleep, Tremor of the hands, Exophthalmos (eyeball protrusion, cornea ulceration, optic nerve streched/vision damage)
How do you differentiate hypo- or hyper- thyroidism in lab?
Hyperthyroidism will have decreased TSH with increased FT3 and FT4 while hypothyroidism will have increased TSH with decreased FT3 and FT4 (slide 18).
How is T3 synthesized?
A large amount of T4 (25%) is converted to T3 in peripheral tissues via deiodination. This conversion takes place mainly in the liver and kidneys. The T3 formed is then released to the blood stream.
How does propylthiouracil inhibit T3?
Impairs peripheral conversion of T4 to T3.
What are the differences between propylthiouracil and methimazole in 1. MOA 2. drug administration / pregnancy use 3. half life and 4. ADRs / contraindications
- Both inhibit thyroid peroxidase reactions (iodination, coupling) and block iodine organification. PTU primarily inhibits peripheral deiodination of T4and T3.
- Both taken orally. 75% PTU binds plasma protein and is therefor safer to use in the 1st trimester of pregnancy while methimazole does NOT bind plasma proteins so is better used in 2nd and 3rd trimester to avoid PTU ADR. Both are teratogenic.
- T1/2 of methimazole is 24 hrs. while PTU is 6-8 hrs.
- Methimazole ADRs include cholestatic dysfunction. PTU causes liver failure so should carefully monitor liver function so should not be used in children except in case of methimazole allergy.
Why do you need to check WBC while taking methimazole?
Can cause agranulocytosis
When do you use iodide?
Preoperative preparation of thyroid gland, Thyrotoxic crisis, and Radioactive iodine fallout
What is the most important side effect of I 131 treatment?
↑Delayed hypothyroidism
↑Stomach, kidney, breast cancer
↑Radiation thyroiditis
sialadenitis (inflammation of a salivary gland)
How do you diagnose thyroid storm?
Life-threatening complication of thyrotoxicosis so will have will have decreased TSH with increased FT3 and FT4 and percipitating factors of Stress, trauma, surgery, radioactive iodine treatment,
Infections, diabetic ketoacidosis, heart disease, and /or Labor.
How do you treat thyroid storm (6 total)?
- supportive measures 2. PTU (anti-thyroid)
- Beta blockers i.e. Propranolol (prefferd due to lipid solubility and CNS entry) or other β blockers lacking partial agonist activity / without ISA i.e. atenolol, alprenolol, metoprolol, sotalol, and nadolol to treat HTN and tachycardia (last two do not reduce conversion, atenolol cannot enter CNS)
- Hydrocortisone (prevents shock, inhibits peripheral T4 to T3 conversion)
- Oral iodides
- Underlying precipitating illness
How do you diagnose myxedema coma?
Non-pitting edema, hypothermia, respiratory depression, LOC
Which B blockers are contraindicated in hyperthyroidism?
B blockers with ISA are contraindicated in hyperthyroidism
How do you treat emergency hypothyroidism , myxedema coma and what are its side effects?
Liothyronine sodium (T3), more cardiotoxic than levothyroxine
