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20 Cards in this Set
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What is the process of synthesis of thyroid hormones?
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Iodide taken up by thyroid gland, converted to iodine by PEROXIDASE
Tyrosine residues in THYROGLOBULIN are iodinated to form MIT and DIT (DIT+DIT = T4, MIT+DIT = T3) T3, T4 transported in blood by TBG (thyroxine-binding globulin, synthesized in liver) |
TRH (hypothalamus) stimulates
TSH (ant pituitary) stimulates T3, T4, thyroid hyperplasia, uptake of iodide |
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How does T4 differ from T3?
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T4 (DIT+DIT): longer half-life, less potent, converted peripherally to T3
Only free hormone is able to activate peripheral receptors |
States assoc with decreased peripheral conversion of T4 -> T3:
Fasting, malnutrition, systemic illness, physical trauma, postop Drugs (propylthiouracil, propranolol, amiodarone) |
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What are the symptoms of thyrotoxicosis?
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Warm skin, sweating, heat intolerance
Tachycardia, increased SV/CO Dyspnea Increased appetite, nervousness, tremor Weight loss, weakness, increased DTR Menstrual irregularity, decreased fertility |
Amiodarone induces hypo/hyperthyroidism
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What are the symptoms of hypothyroidism?
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Pale, cool skin
Cold intolerance, weight gain Bradycardia, decreased SV/CO Hypoventilation Reduced appetite, lethargy, slowing of mental processes Stiffness, decreased DTRs Infertility, decreased libido |
Amiodarone induces hypo/hyperthyroidism
Lithium induces hypothyroidism |
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What is a thyroid storm and the associated symptoms?
How do you treat it? |
Extreme HYPERthyroidism, medical EMERGENCY!
FEVER, tachycardia, delirium, CV DECOMPENSATION, SHOCK, coma! Stress, sx, illness, pregnancy can precipitate this. Tx: PTU (IV), Iodide, Steroids, Propanolol |
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What is a myxedema coma and the associated symptoms?
How do you treat it? |
Due to untreated HYPOthyroidism, medical EMERGENCY!
Hypothermia, hypoglycemia, hyponatremia, psychosis, shock, coma Tx: IV Levothyroxine, supportive |
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What tests should you run to test to test thyroid function?
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TSH levels: most sensitive to evaluate and screen for thyroid disorder
Free T4: gold standard for measuring active hormone levels |
Drugs that change TSH/TT4 levels:
Suppress TSH: glucocorticoids, dopamine, levodopa, and dobutamine Low TT4, elevate TSH: anti-epileptics |
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What states lead to increased TBG levels? Decreased TBG levels?
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Increased TBG
Pregnancy, newborn state, ocps (estrogen), tamoxifen, infectious and chronic active hepatitis, perphenazine |
Decreased TBG
Androgenic steroids, glucocorticoids, salicylates, chronic liver diseases, severe systemic illness, nephrosis |
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What drugs/methods of treatment do we have for hyperthyroidism?
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Thionamides, RAI, Sx
Adjunctive tx: Adrenergic blockers, Iodine, Lithium, Corticosteroids |
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What are the thioamides? What is their MOA and kinetics?
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Propylthiouracil (PTU) and Methimazole (more potent, longer half-life)
Inhibit peroxidase to block iodination of tyrosine residues and coupling of DIT, MIT (cross-sensitivity bw drugs) PTU (additional MOA): inhibit peripheral conversion T4 -> T3 Onset slow (3-4 weeks), concentrate in thyroid gland so LOW maintenance dose |
Methimazole is preferred for compliance, better taste, cost
PTU less likely to cross placenta and enter breast milk, can use both cautiously in pregnancy |
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What are the AEs of PTU and methimazole?
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RASH (use anti-histamines/steroids), arthralgia, leukopenia (benign transient)
Rare: AGRANULOCYTOSIS (sudden onset, watch for flu-like sx's) HEPATOTOXICITY (caution with alcohol and liver dz) |
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When are PTU and methimazole used and what should you monitor?
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Hyperthyroid: Children, young adults (to preserve gland), Thyroid storm, Pregnancy
Adjust dosing monthly (lowest dose), reduce after euthyroid (permanent remission after 1-2 years) Monitor sx's, FT4/TSH, CBC, LFTs |
Pregnancy (hyperthyroid):
Assess with FT4 (TT4 increases due to inc TBG) PTU or methimazole Sx last resort Do NOT give RAI! |
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What is the MOA of Radioactive iodine (RAI or I-131)? When is it used and what are its AEs?
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Disrupts hormone synthesis, destroys follicles and thyroid (concentrates in thyroid)
Use: Elderly, failed thioamide tx (stop thioamide tx and use adjunctive tx for symptomatic management - propanolol) AEs: mild pain/tenderness, thinning of hair, HYPOTHYROID if wipe out thyroid CI in PREGNANCY/NURSING |
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When do you perform surgery/thyroidectomy?
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Carcinoma, compression goiter, CI to thioamides/RAI
AE: Hypoparathyroid (can cut too), Hypothyroid, Hemorrhage, Nerve damage |
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What are the adrenergic drugs used for adjunctive symptomatic control for hyperthyroidism?
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Beta blockers (propanolol) -- also blocks peripheral conversion of T4 -> T3
CCB (diltiazem) if BB CI Use to decrease palpitations, anxiety, tremor, heat intolerance - stop after not tachycardic |
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What is the MOA of iodine and the iodide salts (potassium iodine, Lugol's solution) and what are their uses/AEs in hyperthyroidism?
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MOA: inhibit iodination (synthesis) of hormones and release -- rapid onset
Use: Thyroid storm, Prep for sx (short-term, symptomatic tx), decrease vascularity (cancer) AEs: rash, drug fever, bleeding disorders Iodism: bad taste, burning mouth/throat |
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What is the MOA of lithium and what is its use in hyperthyroidism?
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Inhibit release of formed hormone
Last resort, narrow tx window, lots of AEs (tremor, GI, CNS..) |
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What is the MOA of corticosteroids and when are they used?
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Blunt and delay rise in antibodies to TSH receptor (Graves)
Use: Graves ophthalmopathy, thyroid storm |
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What does iodinated radiocontrast media do and when is it useful?
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Rapidly suppress peripheral conversion T4 -> T3, inhiit hormone release
Use: rapidly reduce T3 in thyrotoxicosis |
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What are the 2 hypothyroid drugs and their toxicity? How should you dose them?
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LEVOTHYROXINE sodium (T4) - slower onset, longer half-life, DOC
LIOTHYRONINE sodium (T3) - higher AE, use when levothyroxine impaired or in comb to improve mood AE: Thyrotoxicosis (reduce dose in elderly, CV disease) Start LOW, go SLOW (check annually, keep on for life), INC dose if pregnant |
Also Liotrix (4:1 comb) -- not used for most, Tx of myxedema coma
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