Kruse: thyroid drugs Flashcards
What are the thyroid agents
- Levothyroxine (T4)
- Liothyronine (T3)
- Liotrix (4:1 ratio of T4:T3)
- Thyroid desiccated
Antithyroid agents
- Radioactive iodie (131 I) Sodium
- Methimazole
- Potassium iodide
- Propylthiouracil (PTU)
What transports iodide iodide into the thyroid gland
NIS
What is an apical cell iodide transport enzyme that controls the flow of iodide across the membrane?
pendrin
where else is pendrin found? clinical implications?
Cochlea; if deficient or absent a syndrome of deafness and goiter called pendred syndrome occurs
Iodide is oxidized by what in the apical cell membrane
thyroidal peroxidase
Agents that inhibit the conversion of T4 to T3 and increase reverse T3 levels include what
- Radiocontrast agents: iopanoic acid and ipodate
- amiodarone
- Beta blockers
- corticosteroids
Give to those with thyroid storm
Drugs that decrease T4 absorption
- Anacids
- ferrous sulfate
- cholestyramine
- colestipol
- ciprofloxacin
- PPI
- bran
- soy
- coffee
Of the T4 and T3 preparations available, what is the preparation of choice for thyroid replacement therapy and why
- T4: levothyroxine
- stability, low cost, lack of allergic foreign protein, easy lab measurement, long half lift so once daily
Which of the antithyroid drugs is not completely absorbed and has large first pass effect
PTU
Which antithyroid is completely absorbed and has slower renal excretion than PTU
methimazole
Describe the antithyroid therapy in pregnancy
- PTU in first trimester
- Methimazole in second and third
Toxicity of methimazole and PTU
- most common: maculopapular pruriis rash at times accompanied by systemic signs such as fever, nausea, and GI distress
- Rare: urticarial rash, vasculitis, a lupus like reaction, lymphadenopathy, hypoprothrombinemia, acute arthralgia, hepatitis (more common with PTU), and cholestatic jaundice (methimazole)
What are the most serious complications of PTU and methimazole
-agranulocytosis (<500)
What are the monovalent anions that block thyroid gland uptake of iodide by competitively inhibiting the iodide transport mechanism
- Perchlorate
- Pertechnetate
- Thiocyanate
What is the MOA of iodides
- inhibit organification and hormone release
- decrease in size and vascularity of hyperplastic thyroid glands
Clinical use of iodide
- Thyroid storm- thyrotoxic symptoms improve rapidly
- Preoperative reduction of a hyperplastic thyroid gland
- Block thyroidal uptake of radioactive isotopes of iodine in a radiation emergency or other exposure
Toxicity of Iodides
-uncommon. Can include: acneiform rash, swollen salivary glands, mucous membrane ulcerations, conjunctivitis, metallic taste
Iodides and pregnancy?
should be avoided since they can cross placenta and cause a fetal goiter
What is the only isotope used for treatment of thyrotoxicosis
(131)I
radioactive iodine is contraindicated in who
Pregnant women or those breast feeding
Beta blockers and management of thyrotoxicosis
- Those without sympathomimetic activity (metoprolol, propranolol, and atenolol)
- improve symptoms but do not typically alter thyroid levels (high doses of propranolol have been shown to reduce T3 levels by about 20%)
What Beta blocker is most commonly used
propanolol
Treatment of myxedema coma
- preparations given IV
- Large loading dose of T4 followed by smaller IV dosing
Treatment of Myxedema and coronary artery disease
-Correction with T4 must be done cautiously to avoid provoking arrhythmia, angina, or acute MI
Treatment of hypothyroidism and pregnancy
- Women who are hypothyroid are typically infertile until restoration of normal thyroid levels
- Maintenance of normal levels is crucial due to fetal brain development dependence on maternal T4
When do you use antithyroid drug therapy in Graves
- most useful in young patients and mild disease
- Methimazole and PTU until remission
- Methimazole is preferred except in pregnancy
treatment of choice in Graves in patients with very large glands or multinodular glands
- thyroidectomy
- 80-90% will require thyroid supplementation
When do u use Radioactive iodine in Graves
- most over 21
- in pts with underlying heart disease or severe thyrotoxicosis and in elderly patients, treatment with antithyroid drugs until patient is euthyroid is preferred
Describe the adjuncts to antithyroid therapy in Graves
- B-blockers w/o sympathomimetic activity
- these control tachycardia, HTN, and Afib
- Diltiazem (calcium channel blocker) can be used to manage tachycardia in pts who Beta blockers are contraindicated
Management of thyroid storm
- Beta blocker to control arrhythmia
- Potassium iodide to prevent release of thyroid hormones
- PTU or methimazole to block hormone synthesis
- IV hydrocortisone to protect against shock and to block conversion of T4 to T3 in peripheral tissue
- Supportive therapy
- in rare situations where the above is inadequate, plasmapheresis or peritoneal dialysis may be used to lower levels of T4
