Thyroid And Anti-thyroid Drugs (Kruse) Flashcards
Describe T4 and T3 clearance and half life in pts with hyperthyroidism
Clearance=increased
Half life=decreased
Describe T4 and T3 clearance and half-life in pts with hypothyroidsm
Clearance=decreased
Half-life=increased
What effect do antacids, ferrous sulfate, cholestyramine, colestipol, ciprofloxacin, PPIs, bran, soy, and coffee have on T4 absorption?
Decrease
Rifampin, rifabutin, phenobarbital, carbamazepine, phenytoin, imatinib, and protease inhibitors have what effect on metabolism of T4 and T3?
Increase –> these are all P450 inducers
What effects will Iopanoic acid, ipodate, amiodarone, B blockers, corticosteroids, PTU, and flavonoids have on thyroid function?
Inhibition of 5’-deiodinase with decreased T3 and increased Reverse T3
IFN-a, IL-2, IFN-b, Lithium, and amiodarone can have what effect on thyroid function?
Induction of autoimmune thyroid disease with hypothyroidism or hyperthyroidism
Of the T4 and T3 preparations available, ___ is the preparation of choice for thyroid replacement therapy d/t its stability, low cost, lack of allergic foreign protein, easy lab measurement of serum levels, and long half-life, which permits once-daily admin
Levothyroxine (T4)
Why T4 preparations over T3?
Although T3 is 3-4x more potent than T4, not recommended for routine therapy d/t short half life, higher cost, difficulty of monitoring its adequacy of replacement by conventional lab tests
T3 best used for short-term suppression of TSH
This thyroid agent is a 4:1 ratio of T4:T3
Liotrix
Methimazole and PTU are what type of antithyroid agents?
Thioamides
Rate of absorption of thioamides? Excretion? Half life? Dose/day?
Rapidly absorbed 50-80% bioavailability Renal excretion Half life 1.5 hrs 3-4 doses/day
This thioamide is not recommended in pregnant women. It is secreted in breast milk at low concentrations and considered safe
Methimazole
Main MOA of thioamides?
Inhibits the thyroidal peroxidase-catalyzed rxns and blocks iodide organification; also inhibits coupling of MIT and DIT to form T3 and T4
__ blocks peripheral conversion of T4 to T3. A significantly greater fall in [T3] and the T3:T4 ratio may occur with PTU and iodine compared to methimazole and iodine
PTU
Most common adverse effects of thioamides?
Maculopapular pruritic rash, at times accompanied by systemic signs such as fever, nausaea, and GI distress
Most serious complication associated with thioamides?
Agranulocytosis. Can be reversed with drug discontinuation and CSFs
Perchlorate, pertechnetate, and thiocyanate are these types of drugs:
What is their MOA?
Anion inhibitors
Block thyroid gland uptake of iodide by competitively inhibiting the iodide transport mechanism
Effects can be overcome by large doses of iodides
MOA of Iodides?
Inhibit organification and hormone release; decrease size and vascularity of the hyperplastic thyroid gland
Clinical use of iodides?
Thyroid storm
Preoperative reduction of hyperplastic thyroid gland
Block thyroidal uptake of radioactive isotopes of iodine in a radiation emergency or other exposrue to radioactive iodine
When should iodides be avoided?
During pregnancy –> can cross placenta and cause fetal goiter
__ is the only isotope used for tx of thyrotoxicosis
131-Iodine –> radioactive iodine
Contraindication of radioactive iodine?
Women who are pregnant or breast feeding
Propanolol (most common), metoprolol, and atenolol can be used in management of___
Thyrotoxicosis
Food or no food with levothyroxine?
Take on empty stomach
Why do you need to be careful when giving T4 to pts with myxedema and CAD?
Avoid provoking arrhythmia, angina, or acute MI
This anti-thyroid is preferred for Graves (hyperthyroidism/thyrotoxicosis)
Methimazole
Adjuncts to antithyroid therapy?
B blockers
Diltiazem (CCB) can be used to manage tachycardia in pts whom B blockers are contraindicated
In thyroid storm:
__ can be used to control arrhythmia
__ to prevent release of thyroid hormones form thyroid gland
__ to block hormone synthesis
__ to protect against shock and to block conversion of T4 to T3 in peripheral tissues/blood
B blockers
Potassium iodide
PTU or Methimazole
IV hydrocortisone
