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E2T1 > Thyroid and Antithyroid drugs DSA > Flashcards

Thyroid and Antithyroid drugs DSA Flashcards

1
Q

Thyroid agents

A
  • Levothyroxine (T4)
  • Liothyronine (T3)
  • Liotrix (4:1 of T4:T3)
  • Thyroid desiccated
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2
Q

Antithyroid agents

A
  • Radioactive iodine (131) sodium
  • Methimazole
  • Potassium iodide
  • PTU (propylthiouracil)
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3
Q

TH biosyn

A
  • NIS (sodium/iodide symporter) transports iodine into the thyroid gland
  • pendrin- controls the flow of iodide across the membrane
  • iodide is oxidized to iodine by thyroidal peroxidase
  • iodine iodinates tyrosine residues in thyroglobulin- form MIT (monoiodotyrosine) and DIT (diiodotyrosine)
  • 2 molecules of DIT combine with thyroglobulin- forms T4
  • 1 molecule of DIT and MIT combine- forms T3
  • T4, T3, MIT, DIT released from thyroid gland
  • T4:T3 ratio within thyroid gland is 5:1
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4
Q

TH transport

A

-T4 and T3 are bound to TBG (thyroxine-binding globulin) in plasma

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5
Q

peripheral metabolism of THs

A
  • T3 is deiodinated to T3 (4x more potent than T4) or reverse T3 (metabolically inactive)
  • T4 may be inact by deamination, decarboxylation, or conjugation
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6
Q

THs- pharmacokinetics

A
  • oral bioavailability of T4- 80%- t1/2 7 days
  • oral bioavailability of T3- 95%- t1/2 1 day
  • abs may be affected by myxedma with ileus (but not by mild hypothyroidism)
  • T4 and T3 clearance- inc with pts with hyperthyroidism; dec with hypothyroidism
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7
Q

drug effects and thyroid fxn- inhibit conversion of T4 to T3 and in reverse T3 levels

A
  • radiocontrast agents iopanoic acid and ipodate
  • amiodarone
  • B-blockers
  • corticosteroids
  • admin to reduce T3 levels in pts who are experiencing a thyroid storm!
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8
Q

drug effects and thyroid fxn- dec T4 abs

A
  • antacids (aluminum hydroxide, calcium carbonate
  • ferrous sulfate
  • cholestyramine
  • colestipol
  • ciprofloxacin
  • proton pump inhibitors
  • bran, soy, coffee
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9
Q

drug effects and thyroid fxn- induce CYP450s

A
  • rifampin, phenobarbital, carbamazepine, phenytoin, imatinib, protease inhibitors
  • inc metabolism of T4 and T3
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10
Q

TH- moa

A
  • TR is bound to DNA at the TRE
  • in absence of H- TR homodimer is bound to corepressor proteins (inactive)
  • T4 and T3 enter cell- T3 enters nucleus- binds to TR- corepressor is released- coactivator binds- homodimer separates
  • TR binds to RXR and gene transcription occurs
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11
Q

Thyroid preparations

A
  • synthetic or of animal origin (rarely used)
  • T4 (levothyroxine)- preparation of choice for thyroid replacement tx- stability, low cost, lack of allergic foreign protein, easy lab measurement of serum levels, long t1/2- once-daily admin
  • T3 is 3x more potent- not recommended for routine replacement tx- short t1/2, higher cost, diff of monitoring
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12
Q

Antithyroid agents

A
  • thioamides
  • anion inhibitors
  • iodides
  • radioactive iodine
  • B-blockers
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13
Q

Thioamides- pharmacokinetics

A
  • PTU- rapidly abs, 50-80% bioavailability, renal excretion, accum in thyroid gland, 3-4 doses a day
  • Methimazole- completely abs, accum in thyroid gland, slower renal excretion than PTU, once-daily dosing
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14
Q

Thioamides- moa

A
  • inhibits the thyroidal peroxidase rxns and blocks iodide organification (blocks the oxidation of iodide in the thyroid gland)
  • also inhibits coupling of MIT and DIT to form T3 and 4
  • PTU- blocks peripheral conversion of T4 to T3
  • hormone synthesis is inhibited!!- requires 3-4 wks of therapy before stores of T4 and T3 are depleted
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15
Q

Thioamides- toxicity

A
  • maculopapular pruritic rash- most common
  • rare- urticarial rash, vasculitis, lupus-like rxn, LA
  • most serious complication- agranulocytosis- can be reverse with drug discontinuation and CSFs
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16
Q

Anion inhibitors- moa

A

perchlorate, pertechnetate, thiocyanate

-block thyroid gland uptake of iodide by inhibiting the iodide transport mech

17
Q

Iodides- moa, clinical use

A
  • inhibit organification and H release- dec the size and vascularity of the hyperplastic thyroid gland
  • thyroid storm, preoperative reduction of a hyperplastic thyroid gland, block thyroidal uptake of radioactive isotopes of iodine in a radiation emergency
18
Q

Iodides- toxicity

A
  • acneiform rash, swollen salivary glands, mucous memb ulcerations, conjunctivitis, metallic taste
  • avoid during pregnancy- can cause fetal goiter
19
Q

Radioactive iodine

A
  • tx thyrotoxicosis
  • admin orally
  • causes destruction of thyroid parenchyma
  • ease of admin, effectiveness, low expense, absence of pain
  • contraindicated in women who are pregnant or breast feeding
20
Q

B-blockers

A
  • w/o intrinsic sympathomimetic activity (metoprolol, propranolol, atenolol)- tx thyrotoxicosis
  • propranolol- most common
  • improve sx of hyperthyroid
21
Q

drug of choice for replacement therpy

A

levothyroxine

  • given on an empty stomach
  • 6-8 wks to reach steady-state levels
22
Q

Hypothyroidism management- myxedema coma

A
  • end state of untreated hypothyroidism- progressive weakness, stupor, hypothermia, hypoventilation, hypoglycemia, hyponatremia, water intoxication, shock and death
  • give IV due to poor absorption!
23
Q

Hypothyroidism management- myxedema and CAD

A

-correction of myxedema with T4 must be done cautiously to avoid arrhythmia, angina, or acute MI

24
Q

Hypothyroidism management- pregnancy

A
  • are typically infertile until restoration of normal thyroid levels
  • maintenance of normal levels is crucial to fetal brain development dep on maternal T4
25
Q

Grave’s disease- management

A
  • Antithyroid drug therapy- young pts with small glands and mild dz- methimazole (preferred- once daily) or PTU (pregnancy)- admin until remission
  • thyroidectomy- very large glands or multinodular goiters- require thyroid supplementation
  • radioactive iodine- preferred tx for pts > 12 yo- 80% develop hypothyroidism and require replacement tx
  • adjuncts to antithyroid tx- B-blockers (control tachycardia, HTN, a fib); diltiazem when B-blockers contraindicated
26
Q

Thyroid storm- management

A
  • B-blockers- control arrhythmia
  • potassium iodide- prevent release of THs
  • PTU or methimazole- block H syn
  • IV hydrocortisone- prevent against shock and block conversion of T4 to T3
  • supportive therapy

E2T1 (6 decks)

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