Thyroid Drugs Flashcards
What is the pathway for thyroid hormones being released onto the target tissue? (5 steps)
CNS → Hypothalamus (TRH) → Pituitary (TSH) → Thyroid (T3/T4) → Target tissue
T3 and T4 provide negative feedback to what?
Pituitary and hypothalamus
Thyroid hormones are regulated by what 2 things?
TSH and iodide
high iodide will block thyroid hormone production
How do thyroid hormones affect BMR?
Increase
Due to the fact that thyroid hormones are important for growth/ maturation (including CNS), hypothyroidism in children is concerning because it can lead to what?
Cretinism
Is T3 or T4 more effective and why?
T3
What type of receptors do T3 and T4 act through?
Nuclear receptors (slow effect in body)
Myxedema is hypo or hyperthyroidism?
Hypothyroidism
myxedema coma = severe hypothyroidism
Do you have high or low levels of TSH with hypothyroidism?
High (primary cause of thyroid gland failure)
Pt presents with slow BMR, hypothermia (cold intolerance), fatigue +/- goiter. What are you concerned for?
Hypothyroidism
Pt presents with fast BMR, tachycardia, fatigue, hot (heat intolerant), tremor, insomnia, and diarrhea. What are you concerned for?
Hyperthyroidism
What are the 2 most common causes of hyperthyroidism?
Grave’s disease and toxic nodular goiter
Grave’s = autoimmune disease, activate Ab to TSH receptor
What are the treatment options for hyperthyroidism? (3)
Surgery, decrease T4/T3, block sxs with beta-blockers
Propranolol and metoprolol drug class?
Beta-adrenergic blocking agents
Levothyroxine drug class?
Thyroid hormone replacement
Liothyronine sodium drug class?
Thyroid hormone replacement
Desiccated thyroid drug class?
Thyroid hormone replacement
Methimazole drug class?
Thioamides
What do thioamides do?
Inhibit thyroid hormone synthesis
Propylthiouracil (PTU) drug class?
Thioamides
Iodide drug class?
Thioamides
Radioactive iodine (131 I) drug class?
Thioamides
What is the MOA for Levothyroxine?
T4- produces N levels of T3/T4 (carefully titrated to individual)
What is the DOC for hypothyroidism?
Levothyroxine
What are the important pharmacokinetic properties of Levothyroxine?
t1/2 = 7 days = ~5 weeks for steady state
What is the MOA for Liothyronine?
T3
When is Liothyronine used?
Initial hypothyroid treatment (not maintenance)
What are the important pharmacokinetic properties of Liothyronine?
t1/2 = 24 hours, shorter duration (than T4)
What is the MOA for Desiccated thyroid?
Mix of T4 and T3 from pigs
When is Desiccated thyroid used?
Hypothyroid (pts with deficiency in peripheral deiodinase enzyme)
What are the SEs for all thyroid hormone replacement drugs?
Hyperthyroidism
fast BMR, tachycardia, fatigue, hot (heat intolerant), tremor, insomnia, and diarrhea
What is the MOA for Propylthiouracil (PTU)?
Blocks conversion of T4 to T3
When is Propylthiouracil (PTU) used?
Hyperthyroid if allergic to Methimazole or pregnant
What are the contraindications for Propylthiouracil (PTU)?
Severe liver injury, acute liver failure (black box warning)
Only use low doses in pregnancy
What is the MOA for Methimazole?
Potent inhibitor of T4 synthesis
What is the DOC for hyperthyroid?
Methimazole (unless allergic or pregnant, then use PTU)
What is the 1st line treatment for Grave’s disease? (2)
Methimazole and PTU
use with beta blocker because effects are gradual as circulating T3/T4 levels last about a week
What are the SEs of Methimazole and PTU? (4)
Itching, skin rash, reversible granulocytopenia/ agranulocytosis, goiter
What is the MOA for iodide?
Decreases synthesis and release of T4/T3 (short term effect ~2-8 weeks)
When specifically is iodide used in the treatment of hyperthyroid?
7-10 days prior to surgery (to prevent thyroid storm) and radioactive emergencies (competes with radioactive iodide to prevent binding)
What is the MOA for Radioactive iodine (131 I)?
Taken into gland specifically
What is the use of Radioactive iodine (131 I) in small amounts (µCi)?
Diagnostic
What is the use of Radioactive iodine (131 I) in large amounts (mCi)?
Gland destruction
In patients where surgery for the treatment of hyperthyroid is indicated but cannot be tolerated, what drug should be used?
Radioactive iodine (131 I)
What is the definitive pharmacologic treatment for Grave’s?
Radioactive iodine (131 I)
What is the preferred treatment for toxic nodular goiter?
Radioactive iodine (131 I)
What are the SEs of Radioactive iodine (131 I)? (2)
Thyroid storm (decrease risk with thioamide), can cause hypothyroidism over time
What are the contraindications to Radioactive iodine (131 I)? (3)
Pregnancy, nursing, mother’s who lack childcare
What is the MOA for propranolol and metoprolol?
Non-specific beta blockers
What is the preferred beta blocker and why?
Propranolol (also inhibits peripheral conversion of T4 to T3)
What is the use of propranolol and metoprolol?
Decrease sxs of hyperthyroidism
What is the contraindication to propranolol and metoprolol?
Asthma (use CCBs instead)
