Medications for Hyperthyroidism and Hypothyroidism Flashcards
_______ is an essential component of T3 and T4
Iodine
What is the more active form of thyroid hormone?
T3
Describe the synthesis and release of thyroid hormone:
The hypothalamus releases TRH
TRH causes release of TSH from the anterior pituitary
TSH acts on the thyroid which is controlling all aspects of thyroid hormone synthesis and release
The thyroid gland secretes more ____ than _____
T4, T3
Where is T4 converted to T3?
The periphery
Drugs used to treat hyperthyroidism (Grave’s Disease) include which antithyroid drugs (thioamines)?
Propylthiouracil (PTU)
Methimazole (Tapazole)
How do PTU and Methimazole work?
Block organification process (production of T3 and T4) by competing with thyroglobulin for oxidized iodide
Reduces synthesis of thyroid hormones
(meds are only useful in overproduction of thyroid hormones)
What is the onset of action of PTU and Methimazole and why?
1-2 weeks d/t thyroid gland stores
In addition to blocking the synthesis of the T3 and T4 what else can PTU block?
Peripheral conversion of T4 to T3
PTU and Methimazole can result in the formation of what? and why?
Goiter
Inhibition of thyroid hormone production leads to an upregulation of TSH release, the TSH is unable to increase thyroid hormone because of the medication, elevated TSH levels stimulate hypertrophy of the thyroid gland in an attempt to increase thyroid hormone synthesis
What common AE associated with PTU and Methimazole?
Pruritic rash early in treatment
Arthralgias (common reason for discontinuation)
What are rare but serious AE of PTU and Methimazole?
**Agranulocytosis- usu. w/in first 90days of treatment, monitor WBC at baseline and if patient has sore throat
Hepatotoxicity (assoc. w/allergic reaction)
Vasculitis (drug induced lupus)
What is the preferred treatment of hyperthyroidism?
Methimazole
Longer half life for once daily dosing
More potent
Less common serious AE than PTU
How often is PTU dosed?
TID (short half life)
PTU can lead to increased tendency to:
bleed d/t depletion of prothrombin levels
What two cases is PTU the preferred method of treatment?
Pregnancy
Acute management of hyperthyroidism (thyroid storm) d/t inhibition of T4 to T3 conversion in the periphery
Most patients respond to treatment with thioamines within ___-____ months.
6-12
For patients who do not respond to thioamines for the treatment of hyperthyroidism what two invasive options do they have?
Radioactive Iodine- Thyroid Gland Ablation
Surgical removal followed by thyroid hormone replacement
When are beta blockers used in the treatment of hyperthyroidism?
While waiting for thioamines to work
How do beta blockers work to provide symptomatic treatment in hyperthyroidism?
Blocks hyperadrenergic effects of thyroid excess (tachycardia, tremors, nervousness)
Blocks peripheral conversion of T4 to T3
What beta blocker should be used during thyroid storm and why?
Esmolol
quick onset of action and short half life
How are iodide salts used to treat hyperthyroidism?
Block conversion of T4 to T3
Quickly but temporarily blocks thyroid hormone release from the thyroid gland (gland is so busy trying to uptake the iodine it can’t make/release thyroid hormone- after it’s all taken up large amounts of T3/T4 release)
Corticosteriods are available as symptomatic treatment for hyperthryoidism because:
Block peripheral conversion of T4 to T3
Suppresses thyroid receptor Ab and inflammation
(prednisone or methylpred)
Two type of hypothyroidism include:
- Primary hypothyroidism (Hashimoto’s Thyroiditis)- autoimmune d/o in which antibodies are produced against TSH receptors, blocking TSH
- Iatrogenic- Ablation, drugs containing iodine, pituitary tumor
What is the drug of choice for hypothyroidism?
Levothyroxine (prodrug of T4)
What is levothyroxine and how does it work?
L-isomer of T4(prodrug)
Body converts it to T3 as needed
Long half-life (6-7days) allows for once daily dosing, wide availability of strengths=ease of titration
What lab values should be monitored in patients taking levothyroxine?
TSH, free T4
s/s of hyperthyroidism indicative of too high a dose
What could an allergic reaction d/t levothyroxine be secondary to?
Dye
Why is T3(Cytomel) not usually given?
Better to have a reservoir of T4 (prodrug) to normalize metabolism over a wide range of conditions
Short half life, 1 day
When is T3 (Cytomel) given?
Life threatening hypothyroidism (myxedema coma), where onset of T3 is more useful
Levothyroxine has many _____ ______.
Drug interactions
Phenobarb, phenytoin, rifampin, and carbamazepine all affect levothyroxine how?
Potent inducers= increase metabolism of drug
PTU, beta blockers, amiodarone, and glucocorticoids all affect levothyroxine how?
Block levothyroxine, decrease T4 to T3 conversion
Which drugs decrease levoythyroxine’s absorption from the gut?
Cholestyramine, sucralfate, kayexelate, FeSO4, Al(OH)3
administer at different time
Drugs/condition that increase thyroid binding globulin (bind T3 and T4 include:
Estrogen (oral contraceptives)
Pregnancy
What three drugs alter thyroid status?
Amiodarone
Lithium
Metoclopramide (Reglan)
How does amiodarone affect the thyroid?
Structurally resembles thyroid hormone
When amiodarone is metabolized it releases iodine which is taken up by the thyroid gland and can suppress the gland (hypo) or increase synthesis of thyroid hormone as well as act on thyroid receptors (hyper)
How does lithium affect the thyroid?
Actively concentrated in the thyroid gland
Body thinks it is iodine
Can inhibit thyroid synthesis leading to hypothyroidism
How does reglan affect the thyroid?
Increases TSH production/release= incr T3 and T4 release
