Exam 2- HPA & Thyroid Flashcards
Somatostatin analogs
- Growth hormone antagonist
- Inhibits release of GH, glucagon, insulin, and gastrin
- Octreotide = long acting
Dopamine D2 receptor agonists
- Growth hormone antagonist
- Bromocriptine
- Effective at inhibiting prolactin release (more than GH) but high doses have some efficacy in small GH secreting tumors
Major secretory product of the thyroid gland
T4 (Thyroxine)
Major active product of the thyroid gland
T3 (Tri-iodothyroine)
Most of the thyroid hormones are transported this way
Bound to thyroxine-binding globin (TBG), prealbumin, or albumin
These thyroid hormones are active
Only free
Problem location- (TRH ↑) TSH ↑, T3-T4 ↓
Thyroid hypofunction
Problem location- (TRH ↑) TSH ↓, T3-T4 ↓
Pituitary hypofunction
Problem location- (TRH ↓) TSH ↓, T3-T4 ↑
Thyroid hyperfunction
Problem location- (TRH ↓) TSH ↑, T3-T4 ↑
Pituitary hyperfunction
Levothyroxine
- Thyroid agent
- Synthetic T4
- Used in hypothyroidism
- AE: nervousness, heat intolerance, palpitation/tachycardia, weight loss
Radioactive iodine
- Antithyroid agent
- I-131
- Used for the treatment of thyrotoxicosis
- Rapidly absorbed, concentrated in the thyroid, and incorporated into storage follicles
- Crosses the placenta and excreted in breast milk (contraindicated)
Thioamides
- Antithyroid agents
- Methimazole & Propylthiouracil
- Propylthiouracil inhibits conversion of T4 to T3 so brings level down faster
- Inhibit thyroid peroxidase-catalyzed reactions blocking iodine organification (prevents binding of iodide to tyrosine)
- AE: Severe hepatitis with PTU and agranulocytosis (infrequent but potentially fatal)
Potassium iodide
- Iodide (antithyroid agent)
- Blocks release of T4 and T3 and inhibits iodine organification
- Reduces size and vascularity of hyperplastic gland (useful as preoperative prep for surgery)
- Use: Must be given AFTER a thioamide to prevent iodine from being used in new hormone synthesis; given a week after RAI, normalizes thyroid function earlier than RAI alone; given to protect thyroid from radioactive iodine fallout (uptake of RAI is inversely proportional to serum concentration of stable iodine)
- Cross placenta and can cause fetal goiter
Beta Blockers
- Useful in controlling tachycardia and other cardiac abnormalities of severe thyrotoxicosis
- Propranolol also inhibits peripheral conversion of T4 to T3
Aspirin & NSAIDs
- Avoid in thyrotoxicosis
- Decrease protein binding (associated with displacement of thyroid hormone from TBG)
- Cause increase in free thyroid hormone
Myxedma & Coronary Artery Disease considerations
- Correction must be done cautiously to avoid provoking arrhythmia, angina, or acute MI
Long-standing hypothyroidism considerations
- Elderly patient’s heart is very sensitive to level of circulating thyroxine
Pregnancy considerations
- Increase in dose may be required to normalize TSH levels
